Adaptation of Plants to Water-Limited Mediterranean-type Environments

Perth, Western Australia

20-24 September 2004

 

 

Factors influencing the productivity and sustainability of agricultural systems in the Mediterranean-climatic zone of Australia

 

Neil C Turner

 

CSIRO Plant Industry, Private Bag 5, Wembley, WA 6913 and

Centre for Legumes in Mediterranean Agriculture, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia

 

 

Abstract.  Mediterranean environments are characterised by hot dry summers and cool wet winters. The native vegetation of Mediterranean-climatic regions is predominantly perennial shrubs and trees intermixed with annual forbs. In southwestern Australia, the spread of agriculture has seen the adapted perennial vegetation replaced by rainfed annual crops and pastures that have subsequently given rise to waterlogging, secondary salinity and loss of productivity in about 10% of the cleared land area. To be economically viable, agricultural productivity needs to increase by about 3% per annum. Yields of dryland wheat, the predominant crop, in the Mediterranean agricultural region of Australia have increased at about 1% per year for the century preceding the 1980’s and since then by 4% per year. The increases have arisen from both genotypic and agronomic improvements. Genotypic increases have arisen from selection for earliness, closer matching of water use to rainfall and soil water availability, early vigour, improved disease resistance and harvest index. Agronomic increases have arisen from early sowing, increased fertiliser use, especially nitrogen, rotations to improve weed control, minimise disease risk and increase nitrogen availability, deep ripping to overcome root constraints and drainage to reduce waterlogging. It is suggested that the rapid increase in yield of wheat in the last two decades has arisen from the rapid adoption of new technologies and the integration of breeding and agronomy. However, the need to reduce deep drainage to make the agricultural systems environmentally sustainable requires the re-introduction of perennial vegetation in the form of belts of trees or shrubs or phase farming systems with perennials such as lucerne replacing annual pastures between the cropping years. To make these systems economically viable will be a challenge.

 

 

Adaptation of wheat to water limited Mediterranean type environments. The contribution of crop management

 

Walter K. Anderson

 

Department of Agriculture Western Australia, 444 Albany Highway, Albany WA 6330

 

 

Abstract. Modern bread wheat has been well adapted for survival and production in water-limited environments since it was first domesticated in the Mediterranean basin at least 8,000 years ago. Adaptation to various environments has been assisted through selection and cross-breeding for traits that contribute to high and stable yield since that time. Improvements in crop management aimed at improving yield and grain quality developed more slowly but the rate of change has accelerated in recent decades.

Many studies have shown that the contribution to yield increases from improved management in the twentieth century has been about double that from breeding. Both processes have proceeded in parallel, though possibly at different rates in some periods, and positive interactions between breeding and management have been responsible for greater improvements than by either process alone.

In southern Australia over the last century management of the wheat crop has focussed on yield improvement, risk management and improvement of grain quality. Adaptation has come to be equated with profitability and recently, with long term economic and biological viability of the production system. 

 

Early emphases on water conservation through the use of bare fallow, crop nutrition through the use of artificial fertilizers, crop rotation with legumes, and mechanisation, have been replaced by, or supplemented with, extensive use of herbicides for weed management, reduced tillage, earlier sowing, retention of crop residues, and the use of ‘break’ crops for management of root diseases.

Yields from rainfed wheat crops in southern Australia have doubled since the late 1980’s and water use efficiency as a consequence has also doubled. The proportion of the crop in Western Australia that qualifies for premium payments for quality has increased 3-4 fold since 1990. Both these trends have been underpinned by the gradual elimination or management of the factors that have been identified as limiting grain yield, grain quality or long term viability of the cropping system.

 

A comparison of the genetic basis of adaptation to low rainfall environments in barley

 

Stewart J CoventryA, Michael BaumB, Stefania GrandoB, Salvatore CeccarelliB, Haitham SayedB, Andrew BarrA, Paul EckermannC, and Jason EglintonA

 

ASchool of Agriculture and Wine, University of Adelaide, PMB 1, Glen Osmond, SA 5064, Australia

BInternational Center for Agricultural Research in the Dry Areas (ICARDA), PO Box 5446, Aleppo Syria

cBiometrics SA, University of Adelaide/SARDI, PMB 1, Glen Osmond, SA 5064, Australia.

 

Abstract.  Barley grown in the low rainfall environments of southern Australia commonly encounters drought stress and hostile soils that reduce yield. Therefore, adaptation to these environments involves tolerance to a multitude of stresses, many of which indirectly influence the ability of the plant to yield under drought. The genetic basis of adaptation to low rainfall environments has been assessed using mapping populations specifically designed for this purpose. These mapping populations involve those developed in Australia and by ICARDA. The reciprocal exchange of populations, and assessment in low rainfall environments in Australia, Jordan, and Syria, has allowed for a comparison between these low rainfall environments in terms of the genetics of adaptation, which this paper describes. Yield, physical grain quality, and traits involved in adaptation were assessed as appropriate in these environments, and multi-environment QTL mapping used to determine QTL coincidences and stability.

 

 

 

Water and nitrogen co-limitation in Mediterranean-type agro-ecosystems

 

Victor Sadras

 

CSIRO Land and Water & APSRU, Waite Campus, PMB 2, Glen Osmond 5064, Australia

 

Abstract.     Availability of water and nitrogen are interplaying factors restricting primary production of semiarid and arid ecosystems. Two decades ago, on the bases of economic analogies, Bloom et al. formalised a theorem stating that plant growth is maximised when all resources are equally limiting (Annual Review of Ecology and Systematics 16, 363-392). The lack of appropriate methods to quantify co-limitation has largely precluded empirical tests of the concept.

This paper discusses alternative indices of co-limitation, with emphasis on water and nitrogen, and their application to dryland faming systems. Curves relating crop production (W) and availability of resource i

 

(Ai) allow for the definition of an index of limitation Li as the slope of the W vs Ai curve normalised by the ratio W/A. Co-limitation between two resources a and b can thus be defined as Cab = 1 – |La -Lb|.  This Cab index can be applied to a broad range of resources but has an unavoidable element of circularity in relating back to W, as they are related by definition. Modelled indices of co-limitation could largely solve this problem of lack of independence with measured crop responses, but most models only allow for few resources, i.e. water, nitrogen and radiation. 

Modelled scalars quantifying the degree of water (SW) and nitrogen stress (SN) were integrated in seasonal indices to quantify the aggregated intensity of both stress (SWN = SW  + SN), the degree of water and nitrogen co-limitation (CNW  =  1 – |SW -SN|), and the integrated effect of stress and co-limitation (SCNW = CWA/SWN ). The expectation of grain yield being inversely proportional to stress intensity and directly proportional to degree of co-limitation was investigated using wheat yields measured in an experiment where season and rotation were the main sources of variation. Measured grain yield (range 2.5 to 4.8 t/ha) was related to SWN combining water and nitrogen stress (r = -0.66, P = 0.02), the co-limitation index CWN  (r = 0.71, P = 0.01), and the SCWN  index combining stress intensity and degree of co-limitation (r = 0.81, P = 0.001); SWN  and CWN  were unrelated (P > 0.23).  

 

 

 

Research requirements for improved water-use efficiency

 of cereal-based systems, with emphasis on Western Australia

 

Len J. Wade and Tina Botwright

 

The University of Western Australia, School of Plant Biology M084, Perth, Australia

 

Abstract.  The farming system in the south-west of Western Australia is quite recent by global standards, with substantial areas cleared within living memory.  The Mediterranean climate of cool wet winters and hot dry summers provided a clear seasonality for farming. The initial system was wheat-fallow, with sheep grazing crop residues in summer and volunteer weeds after the autumn break. As soil fertility declined, self-regenerating annual legumes such as sub-clover were introduced.  With the advent of no-till, herbicides and machinery for direct drilling, sowing could be brought forward and a wider range of crops sown, including lupin, chickpea, faba bean, field pea and canola.  But extensive land clearing and replacement of deep-rooted perennial native vegetation with shallow-rooted annual crops dramatically altered the water balance, resulting in rising water tables and salinity, and indications of rainfall decline.  A sustainable system is urgently needed to maintain soil fertility, to minimize recharge and keep water tables down, to manage salt-affected lands, and to prevent desertification. Within this context, the agronomy and physiology of wheat- and barley-based systems need to be improved for a long-term sustainable, productive and profitable system. Hostile subsoils are a major challenge to the entry and function of plant roots, and cultivars and systems are urgently required to capture the soil water productively and stabilize the farming system.  This paper reviews the challenges faced, progress to date, approaches used to address these concerns, and research requirements for the future.  Six priority areas for research attention are discussed, that should be of interest in Mediterranean environments in Australia and elsewhere. Interdisciplinary collaboration at various levels of integration, system, plant and molecular level, is considered essential for success.

 

 

 

 

 

 

 

 

 

 

 

 

 

A decade of research on cool season grain legumes in dryland environments: Lessons learned

 

K.H.M. SiddiqueA, K.L. ReganA,B, J. BergerA,  P.F. WhiteA,B, N.C. TurnerA,C and T.N. Khan A,B

 

ACentre for Legumes in Mediterranean Agriculture, The University of Western Australia,

35 Stirling Highway, Crawley WA 6009

BDepartment of Agriculture Western Australia. Locked Bag 4, Bentley WA 6983  
 CCSIRO Plant Industry, Private Bag 5, Wembley WA 6913

 

Abstract.  The adaptation and yield of a range of cool season grain legumes (chickpea, faba bean, field pea, lentil, narbon bean, vetch and lathyrus) were studied across a wide range of dryland environments in south-western Australia.  Soil pH, soil clay content and rainfall were the most important environmental factors identified in determining seed yield. Field pea, faba bean, vetch and narbon bean generally produced higher dry matter and seed yields compared with the other species.  There were clear species by environment interactions.  At low yielding sites, field pea produced the greatest seed yield, while at high yielding sites, faba bean, most often produced the highest seed yield. All species used the same total amount of water during the growing season, but the pattern of water-use varied markedly amongst species. Species that used more water after flowering produced higher yields. Species that flowered early produced rapid ground cover and dry matter production used more water during the post-flowering period. Agronomic studies have identified optimum seeding rates, depths and times of sowing for key species for specific environments in WA. Recent studies using a wide range of chickpea germplasm suggest that early phenology together with high harvest index and early generation selection undertaken in the target environment are necessary for further yield improvement of chickpea in low rainfall dryland environments. Improvement in the adaptation of cool season grain legumes to short season Mediterranean-type environments requires increased early growth for rapid ground cover, greater dry matter production, tolerance to low temperatures, and early flowering, pod and seed set prior to the onset of terminal drought.  Development of varieties with improved disease resistance and greater yield stability will accelerate the adoption of cool season grain legumes in the dryland farming systems of southern Australia.

 

Lupin – the largest grain legume crop in Western Australia

 

Bevan J. Buirchell A and Bob French A, B

 

A Department of Agriculture, Locked Bag 4, Bentley, W 6983

B Dry Land Research Institute, Department of Agriculture, Merredin, WA 6415

 

Abstract.   Narrow-leafed lupin (NLL) (Lupinus angustifolius L.) has become the most successful grain legume in the Western Australian with production averaging over 800,000 tonnes per annum.  Over the last 30 years this species has been adapted to the WA environment through exploitation of its natural abilities to grow in a Mediterranean climate and through breeding activities.  NLL is a native of the countries around the Mediterranean Sea and as such has evolved to grow under winter rainfall conditions with a terminal spring drought.  Wild accessions have a wide range of flowering times from 75 to 145 days, with the later types requiring vernalization.  They are found growing at sea level to 1700 m in nearby mountains and in annual rainfall areas of 300 mm to 1750 mm. The species has a diversity of ecotypes.  Adaptation to drought in both wild and domesticated genotypes is principally by drought escape, through early flowering and maturity; drought avoidance through deep rooting on appropriate soils; and early stomatal closure as water deficits develop. NLL has very little tolerance of tissue water deficit compared to other crop species.  It has considerable developmental plasticity, which allows it to remain determinate under poor growing conditions, yet respond to good rainfall and longer seasons by becoming indeterminate. It is well adapted to the mildly acid sandy soils that dominate the central and northern wheatbelt of WA. Apart from integrating all the genes needed for domestication, the breeders have developed other characteristics that have allowed good production while avoiding the terminal drought. These characteristics include an earlier flowering gene (Ku); early maturity; better pod filling characteristics that more efficiently divides the sink between pod fill and expansion, and branch development; disease resistances which prevents yield loss; and increased harvest index. They have all contributed to lupins expanding into shorter season and lower rainfall areas.  Early vigour is now being explored for biomass accumulation before seed fill commences.  The revolution in grain legume production in WA has been the result of recognising the natural adaptation of NLL, and the exploitation and modification of this species by plant breeders, physiologists and agronomists.

 

 

Wild and cultivated Cicer species - different evolutionary paths lead to different phenological strategies that can be exploited to broaden the adaptation of chickpea

 

Jens D. BergerA, Neil C. TurnerA,B, and Renee P. Buck B

 

A Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009. Email Jens.Berger@csiro.au

BCSIRO Plant Industry, Private Bag 5, Wembley, WA 6913

 

Abstract.  In contrast to its annual, cool-season wild relatives, the chickpea (Cicer arietinum) developed as a post-rainy season, spring-sown crop early in its evolution.  We suggest that these different life cycles imposed different selection pressures on the wild and cultivated Cicer species, and that as a result different phenological strategies are likely to be expressed. To test this hypothesis, diverse wild and cultivated Cicer species from a wide range of habitats were subjected to different cold treatments, and evaluated in the field.  In terms of days to flowering, C. arietinum, C. yamashitae, and most C. judaicum accessions were unresponsive to vernalization, whereas the opposite was the case for C. echinospermum and C. pinnatifidum. C. bijugum and C. reticulatum were intermediate, with around 50% of accessions vernalization responsive. Since both C. echinospermum and C. reticulatum are commonly used in chickpea improvement programs this has important ramifications for breeders.  The time interval between flowering and podding was significantly smaller in wild Cicer species (mean: 5-7 days) than in the cultigen (mean: 14 days), and this may be a reflection of reduced susceptibility to cold temperatures in the wild species, a trait urgently required in chickpea. 

 

Evaluation of Helicoverpa and drought resistance in desi and kabuli chickpea

 

 S.S.Yadav A, J. Kumar A , Suresh Kumar A , Shoraj Singh A  and V.S. Yadav A , Neil C. TurnerB,C, Robert ReddenD

 

A Division of Genetics, Indian Agricultural Research Institute, New Delhi-110012, India

B CSIRO, Plant Industry, Private Bag 5, Wembley, Wembley, WA 6913, Australia

C Centre for Legumes in Mediterranean Agriculture, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia

D Victorian Department of Primary Industries, Grains Innovation Park, Horsham, Vic 3401, Australia

 

Abstract.  In India, pod borer (Heliocoverpa) reduces chickpea yields by almost 20% each year and terminal drought is known to reduce yields in rainfed chickpea, but the magnitude of the reduction has not been quantified. Sixteen hundred lines of desi chickpeas and 1400 lines of kabuli chickpeas were evaluated over four seasons for yield losses arising from pod borer infestation at the Indian Agricultural Research Institute, New Delhi, by spaying half the plots to prevent pod borer infestation and allowing the other half to be infested. The yield losses varied from 7% to 37% depending on the chickpea type. Medium-seeded desi types with a tall erect and open canopy showed less damage compared to bold seeded and spreading kabuli types. Ninety lines were then further evaluated under irrigated and rainfed conditions. Yield losses due to pod borer infestation were always greater in the irrigated chickpeas than in the rainfed chickpeas. Further, the terminal drought reduced yields by 10% to 38% depending on plant type. The yields in the kabuli chickpea lines were reduced more by terminal drought than in the desi types due to a greater reduction in the number of branches and pods per plant in the kabuli compared to the desi lines. The results suggest that variation for some pod borer resistance and drought resistance is available in chickpea and should be exploited.

 

 

 

Differential effects of soil water deficit on plant function and their use in crop management

 

Jacques Wery

 

UMR System (Agro.M-Cirad-Inra), Cirad TA 40/01, Av. Agropolis, 34398 Montpellier Cedex 5, France

 

Abstract. Extensive studies have been conducted over the past 30 years on the effects of soil water deficit on the major functions of cultivated plants. Empirical relationships have been established between indicators of the soil water deficit experienced by the plant (for example predawn leaf water deficit or the Fraction of Transpirable Soil Water, FTSW) and the reduction of plant transpiration, net carbon exchange rate, growth of leaf area and reproductive development, in comparison with well watered plants. They have been extensively used to develop water stress modules in crop models, to compare genotypes and to justify more fundamental research on root signals and plant response to drought. Simultaneous analysis of the effect of soil dehydration (most frequently represented by FTSW) on these various functions at the various phases of the crop cycle, have been conducted in our research unit in a broad range of crops covering annuals (Pisum sativum, Cicer arietinum, Phaseolus vulgaris, Vigna unguiculata) and perennials legumes (Medicago sativa, Trifolium repens), Helianthus annuus, Gossypium hirsutum and more recently Vitis vinifera, in various conditions (from pots in the greenhouse to farmer’s fields). They consistently indicate that leaf area development is the most sensitive process to soil water deficit, with branching being more sensitive than leaf emergence and growth on the main stem. Net carbon exchange rate and the various steps of reproductive development are less sensitive to drought, thereby explaining why grain/fruit yield and or quality can be increased by a moderate drought in annuals crops, in perennial forage crops and in vineyards. In legumes, N2 fixation is more sensitive to soil water deficit than nitrate assimilation and grain yield, suggesting a strong dependency of N2 fixation to nitrogen demand by vegetative growth. Other traits of plant adaptation to drought at the crop level, such as reduction of plant cycle duration, improvement of water use efficiency, increase of harvest index (in case of early drought), and to some extend osmotic adjustment, can be explained by the observed differential effects of soil dehydration on the various plant functions. These results have been used to develop deficit irrigation strategies using tensiometers and to develop tools for in-field diagnosis of drought stress experienced by the crops, especially for seed production and grape production.

 

 

 

The improvement of crop yield in marginal environments using “on-farm” seed priming

 

David Harris

 

Centre for Arid Zone Studies, University of Wales, Bangor, Gwynedd, LL57 2UW, United Kingdom

 

Abstract. On-farm seed priming with water is a low-cost, low-risk technology that is easily adopted by resource-poor farmers and which increases the yield of tropical and sub-tropical annual crops in marginal areas. Such yield increases result from a combination of better crop establishment and improved individual plant performance. The effects of seed priming on plant growth and development are consequences of faster germination, emergence and more vigorous early growth. Data from in vitro, on-station and on-farm experiments are presented and discussed. Recent work has tested opportunities for resource-poor farmers to use seed priming as a vehicle for applying biofertilisers (rhizobia), micronutrients, e.g. molybdenum, and systemic fungicides. Preliminary results suggest strongly that these interventions are not only very effective (over and above the already-demonstrated benefits of priming with water alone) but also offer significant cost savings to farmers. Lowered costs are particularly attractive to farmers in marginal areas and increase the likelihood of adoption of new technologies.

Observations in the field have shown that some primed crops show enhanced resistance to disease, either as a consequence of increased vigour, altered phenology or due to some more fundamental mechanism associated with exposure of seeds to anaerobic conditions during priming. Results from preliminary investigations to test the latter hypothesis are presented and discussed. Seed priming is a practical and effective way for resource-poor farmers to increase crop productivity. It is particularly well suited to small-scale, non-mechanised agriculture in warm climates where soil moisture at sowing is the limiting factor rather than low temperature. Nevertheless, the effectiveness of seed priming should be evaluated in similar climates in more developed countries. If it were found to be effective, adaptation of the approach to mechanised systems would be a priority.

 

 

 

 ‘On Farm’ Issues -sustainability

 

Peter Macleay, Claire Macleay

 

‘Kareela’, PO Box 222 Kojonup, Western Australia    6395

 

 

Abstract.   This paper discusses the pressures on agriculture to be sustainable.  What is agriculture supposed to sustain? Ultimately agriculture is responsible for providing the sustenance of this civilization.  Is our agriculture the worst sector of this society?  We cannot conclude that it is.

Economic forces have been good at producing productive innovation in the economy and have been the main driver for the success of our civilization.  However, we can demonstrate that economists do not value the future highly, so we all consume ever increasing amounts of the world’s resources, with little thought of the future.

 

The growth in the world’s population continues, as does consumption per head. Agriculture has an admirable track record in satisfying this increase in consumption.  There are challenges facing agriculture but it is the demands placed on it to continually produce more for less, and with less fresh water and arable land available. It is these pressures that are ultimately unsustainable.

 

 

 

 

Drought resistance, water-use efficiency and yield potential – are they compatible, dissonant or mutually exclusive?

 

A. Blum

 

Plantstress.com, PO Box 16246, Tel Aviv 61162, Israel

 

 

Abstract.  This presentation is a concept review paper dealing with a central dilemma in understanding, designing and acting upon crop plant improvement programs for drought conditions.  The association between drought resistance (DR), water-use efficiency (WUE) and yield potential (YP) is often misunderstood which can lead to conceptual oversight and wrong decisions in implementing breeding programs for drought-prone environments. While high yield potential is the target of most crop breeding programs, it might not be compatible with superior drought resistance. On the other hand high yield potential can contribute to yield in moderate stress environments. Plant traits that enhance yield potential should therefore be reviewed in the context of their effect on and interaction with DR and WUE on the background of the prevalent drought profile in the target environment. Plant production in water limited environments is all too often affected by constitutive plant traits that allow maintenance of plant water status rather than by strictly stress adaptive responses that support plant function at low water status. A major adaptive response sustaining crop production under drought stress is osmotic adjustment (OA). Despite past voiced speculations, there is no proof that OA entails a cost in terms of reduced yield potential. WUE for yield is often equated in a simplistic manner with DR. The large accumulation of knowledge on crop WUE as derived from research on carbon isotope discrimination allows some conclusions to be reached on the relations between WUE on one hand and DR and YP on the other. Briefly, apparent genotypic variations in WUE are normally expressed mainly due to variations in water use (WU; the denominator). Reduced WU which is reflected in higher WUE is generally achieved by plant traits and environmental responses that reduce YP. Improved WUE on the basis of reduced WU is expressed in improved yield under water limited conditions only when there is need to balance crop water use against a limited and known soil moisture reserve. However, under most dryland situations where crops depend on unpredictable seasonal rainfall, the maximization of soil moisture use is a crucial component of drought resistance (avoidance) which is then often expressed in lower WUE. It is concluded that the effect of a single “drought adaptive” gene on crop performance in water-limited environments can be assessed only when the whole system is considered in terms of DR, WUE and YP.

 

 

 

Comparative eco-physiology of Cicer sp.

 

Roi Ben-David and Shahal Abbo

 

RH Smith Institute of Plant Science and Genetics in Agriculture, The Levi Eshkol School of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel

 

Abstract. As a rule, allelic variation in wild progenitors of crop plants is much wider compared with their domesticated counterparts. Consequently, wild relatives are recognized as valuable sources of allelic variation for biotic and abiotic stress resistance. Such useful alleles can be easily introduced from species within the primary genes pools, and to a much lesser extent from the secondary gene pools. However, even distantly related wild relatives, from the tertiary gene pool (cross incompatible with the cultigen), may serve to increase our understanding of the biology of crop plants and may help breeders to improve crop performance under stress situations. The successful concept of comparative physiology and ecology (widely used in cereals) was applied to Israeli populations of Cicer judaicum. Flowering time vernalization response of a representative C. judaicum collection was compared with domesticated chickpea and its Turkish wild progenitor C. reticulatum. Considerable year-to-year variation in flowering time was observed. In line with its latitude of origin, C. judaicum has a lower vernalization response and stronger temperature response compared with C. reticulatum. Additional options for using wild annual Cicer species will be briefly discussed.

 

 

Seed and pod water relations of Chickpea under wet and dry soil conditions

 

Ken Shackel A Hamid AhmadiA and N. C. Turner B

A Department of Pomology, University of California, Davis, CA, USA 95616

B CSIRO Plant Industry, Perth, Western Australia

 

Abstract.  Seed growth (pod filling) is a relatively drought resistant process in chickpea, and previous research has shown that the water relations of the seed coat, and hence presumably the seed as a whole, is essentially independent of the water relations of the parent plant.  When plants in dry soil are irrigated, stem (covered leaf) water potential recovers quickly, with an equivalent recovery in pod water potential, as measured either by the pressure chamber, or by an increase in the turgor of cells in the outer pod wall.  In contrast, the turgor of cells in the seed coat remains relatively constant and relatively low (about 0.1 MPa), despite the fact that the seed coat is vascularized, maternal tissue.  The outer and inner pod wall of chickpea are separated by a zone of very tough, lignified cells however, and hence the increase in outer pod wall water potential may not indicate a similar increase in inner pod wall.  Both the outer pod wall and seed coat are convex surfaces and hence can be viewed relatively easily for the purpose of measuring cell turgor with the turgor pressure probe, but the inner pod wall is concave and can not be viewed easily.  Attempts were made to recurve a flap of pod wall to make the inner surface more accessible, but  generally low and variable cell turgors, which did not respond well to irrigation, were measured using this technique.  Using a more invasive technique involving removal of most of one half of the pod as well as the seeds, but leaving the opposite half undisturbed, we were able to document clear increases in the turgor of inner pod wall cells upon irrigation of previously dry plants.  Unlike cells of the outer pod wall, inner pod wall cells were delayed in their response to irrigation, but by about 20h, the overall increase in cell turgor corresponded to the overall increase in stem water potential exhibited by the plant.  Since the water status of both the inner and the outer pod walls responds to irrigation, the funiculus may represent a likely candidate zone of isolation between the pod and the seed, but the prevention of water potential equilibrium across this zone, despite maintenance of phloem transport to the seed through it, is difficult to reconcile with our current understanding of symplastic and apoplastic water flow in plants. 

 

 

Can water use and yield of annual crops be increased on soils with physicochemical constraints using primer-plants?

 

Stephen L. DaviesA, James G. NuttallB, Roger D. ArmstrongB, Matthew H. McCallumAC, John A. KirkegaardA and Mark B. PeoplesA

 

A CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601

B Department of Primary Industries, Private Bag 260 Horsham, Victoria 3401

C Present address: AgConsulting, Ardrossan, SA, 5571

 

 

Abstract. Crop root growth in alkaline subsoils of south-easterrn Australia is commonly restricted by a range of soil physico-chemical constraints.  These include salinity, boron toxicity and compacted subsoils with high bulk density. Despite this the observed growth and success of some perennial pasture species on these soil types suggests their roots are capable of penetrating and surviving in these hostile subsoil conditions. The roots of these species may modify the soil through the creation of macropores and induce chemical changes as a consequence of root function. These changed soil conditions may be advantageous for following annual crops, thus the preceding species acts as a primer-plant. Ideally primer-plants need to have a root system that will rapidly penetrate to depth and explore the subsoil.  The practicality of such a system will also rely on the primer phase being as short as possible, preferably one year in regions of intensive cropping and for it to have some use wither as fodder or in nitrogen fixation. The ability of a range of potential primer-plant species to colonise hostile subsoils, as evidenced by their water use to depth, is being examined at a field site with a sodic (ESP ranges from 12 to 28 at 1.4 m) and saline (ECe ranges from 4-10 dS/m in the 0.4-1.0 m layer) subsoil.  Sulla (Hedysarum coronarium) and tall wheatgrass (Thinopyrum ponticum) extracted water to the greatest depth (1.2 m) in the first year of growth. In comparison, lucerne (Medicago sativa), melilotus (Melilotus albus), phalaris (Phalaris aquatica) and tall fescue (Festuca arundinaceae) used water to a depth of 0.9 m in the same period, while the annual subclover only used water to 0.7 m. In a second study, a rainfall simulator was used to measure the impact of perennial species on water infiltration into the subsoil at two sites with known subsoil constraints at Temora in southern NSW and Birchip in the Victorian Mallee.  A lucerne phase doubled the steady state infiltration rate into the subsoil at Birchip and more than quadrupled the rate at Temora compared with the subsoil under an annual cropping rotation. The impact of these changes on the water use and yield of subsequent crops was examined at the Temora site. Both wheat and canola in at least one instance used significantly more water (ca.20 mm) from the soil profile following lucerne compared with those crops following other annual species. For canola this increased water use corresponded to a 0.2-0.4 t/ha increase in yield. These studies indicate that the roots of some perennial pasture species can successfully colonise and modify hostile subsoils and can potentially increase water use and yield of subsequent annual crops.  Sulla and tall wheatgrass are two such examples that appear capable of penetrating hard and hostile subsoils to greater depth than annual species thus making them potential primer-plants.

 

 

Water and nutrient use efficiencies in different wheat genotypes

 

Xi-Ping Deng A, Ming-li Huang B, Yong-hui Yuan A and Shinobu InanagaC

 

AInstitute of Soil and Water Conservation, Chinese Academy of Sciences, Shaanxi 712100, RP.China

BNorthwest Sci-Tech University of Agriculture and Forestry, Shaanxi 712100, RP.China

CArid Land Research Center, Tottori University, Hamasaka 1390, Tottori 680, Japan

 

Abstract.  Soil water and nutrient deficiency are two major limiting factors of wheat production in semiarid and eroded areas of China. To improve the water and nutrient use efficiencies of wheat is one means of achieving high yields. In this study, the water and nutrient use efficiencies of six wheat genotypes, which are very important in the evolution of wheat, were determined and to ascertain the evolutionary relationship of wheat water use efficiency and nutrient use efficiency and the effects of different water and nutrient supply on it.  The main results show that water use efficiency (WUE) for biomass and for grain yield increased during the evolution of wheat from diploid to tetraploid and hexaploid. The trend of WUE in different wheat genotypes was Triticum aestivum (AABBDD) > Triticum dicoccum (AABB) > Triticum dicoccoides (AABB) > Aegilops squarrosa (DD) > Triticum boeoticum (AA) > Aegilops speltoides (BB). The increase in the WUE of wheat was correlated with the increase of CO2 assimilation and its translocation, and with the reduction of water consumption. The trends of nitrogen-, phosphorus- and potassium- use efficiencies for grain yield increased significantly with the increase of wheat ploidy. It suggested that wheat nutrient use efficiency for grain is mainly controlled by genotype, and it was a stable genetic property. Water stress elevated the nutrient use efficiency for biomass of wheat, but high fertilizer decreased it. High fertilization treatment decreased the leaf water potential and relative water content of wheat at the jointing stage, but increased the leaf relative water content at the heading stage under water stress. It is implied that water stress could postpone the effective time of fertilizer. So the amount of fertilizer should be reduced in farming practice if water stress occurs at the jointing stage, and be increased if water stress happens at the heading stage.

Optimal sowing time and seeding rate for winter-sown, rain-fed chickpea in a cool Mediterranean area

 

Sui-Kwong Yau

 

Faculty of Agricultural and Food Sciences, American University of Beirut, Bliss Street,

P.O. Box 11-0236, Beirut, Lebanon

 

Abstract. Chickpea (Cicer arietinum) is one of the most important legume crops in West Asia and North Africa. In the region, farmers are expected to take up winter sowing of chickpea on a large scale in response to the reports that winter-sown chickpea gave higher yields than the traditional sowing in the early spring and the availability of new chickpea varieties tolerant to Ascochyta blight and suitable for winter sowing. The objectives of this study were to find the optimal sowing month and seeding rate for winter-sown chickpea, and whether there is a sowing-date by seeding-rate interaction. Two field experiments were conducted under rain-fed conditions at the Agricultural Research and Educational Center (33° 56’ N, 36° 05’ E, 995 m a.s.l.; long-term annual precipitation: 513 mm and mean temperature: 13.9°C) in the Bekaa Valley of Lebanon. The most widely grown chickpea cultivar Janta-2’ was used. The first experiment consisted of two sowing dates: autumn (Nov) and early spring (Mar), and three seeding rates: 20, 40 and 60 seeds m-2. The experiment was conducted in a RCB design with 4 replicates over 2 years.  In the second experiment, there were three sowing dates: Nov/Dec, Jan and Feb, which was conducted in a RCB design with 3 replicates over 3 years. The first experiment showed that autumn sowing gave higher seed yield than early-spring sowing. However, seeding rates had no significant effects on yield and sowing-date by seeding-rate interaction was non-significant, indicating the normal seeding rate used in the traditional spring-sowing would be suitable for winter-sowing. In the second experiment, sowing in Jan gave similar seed yield as Nov/Dec sowing, and both gave higher yield than sowing in Feb. This result was similar to those obtained for winter cereals, i.e., earlier sowing leads to higher seed yield. Results of this study clearly showed that farmers in the high-elevation Bekaa Valley of Lebanon should shift their sowing date for chickpea from early spring to autumn or early-winter, i.e., a similar sowing time as barley, wheat and lentil crops.

 

 

Genomic approaches to improve drought tolerance in cereals

 

Roberto Tuberosa and Silvio Salvi

 

Department of Agroenvironmental Science and Technology, Viale Fanin 44, 40127 Bologna, Italy

 

 

Abstract. Genomic approaches offer new opportunities for the identification, selection and cloning of genes affecting drought tolerance, including those underlying the expression of QTLs (Quantitative Trait Loci). The dissection of the genetic basis of quantitative traits into their single components provides a more direct access to valuable genetic diversity for the physiological processes and morphological traits that influence the adaptive response of crops to drought. This, in turn, enables us to deploy marker-assisted selection (MAS) for enhancing crop performance. Notwithstanding the impressive progress in molecular techniques and the large number of QTLs that have been shown to influence yield in drought-stressed crops, the impact of MAS and other applications of genomics on the release of drought-resilient cultivars has so far been negligible. We will analyze the reasons for this limited applicative impact and review the potential of a number of emerging genomics platforms (e.g. microarrays) for more effectively selecting drought-tolerant cultivars. The results of a number of QTL studies will be analysed. QTL discovery should be viewed as the first step of a longer process aimed at identifying the molecular polymorphism of the functional variation underlying the QTL. Microarrays and other post-genomics platforms will facilitate the identification of candidate genes responsible for the QTL. The cloning of major QTLs will offer additional opportunities to unlock the allelic richness present in germplasm collections and for its exploitation via a more precise MAS and/or via genetic engineering. The successful exploitation of MAS and genomics to enhance drought tolerance will only be possible within an interdisciplinary context and relying on a thorough field assessment of the selected materials. New and more informative high-throughput platforms capable of reducing the cost of molecular profiling coupled with an increasing capacity in genome sequencing hold great promise that genomic approaches will positively impact the release of more drought-resilient cultivars. Although it is not possible to predict to what extent genomics will eventually impact conventional breeding practices, we remain confident that future progress toward a more sustainable agriculture will be accelerated through a more systematic discovery of the function of the genes influencing yield under water-limited conditions and a deeper understanding of their interactions with the environment.

 

 

Maintenance of root growth under water deficits by ABA accumulation: prevention of high levels of reactive oxygen species in the root growth zone

 

Robert E. Sharp A, In-Jeong Cho A and Mayandi Sivaguru B

 

A Department of Agronomy and B Molecular Cytology Core Facility, University of Missouri, Columbia, Missouri 65211, USA

 

 

Abstract. Our previous work showed that accumulation of abscisic acid (ABA) is required for root growth maintenance under water deficits in maize seedlings. Reactive oxygen species (ROS) are produced in greater amounts in stressed tissues. We are investigating the hypothesis that ABA accumulation functions in regulating the antioxidant system to maintain ROS at non-damaging levels in roots growing under water deficits. Levels of ROS in the root growth zone were studied with the fluorescent dye Carboxy-H2DCFDA, and using stereo- and confocal-microscopy. The effect of ABA deficiency under water deficits was studied using the vp14 mutant, in which ABA levels are deficient in water-deficient but not well-watered roots.  Under well-watered conditions, ROS levels were low in roots of both wild-type and vp14 seedlings. Under water deficits, ROS levels were slightly greater in the growth zone of wild-type roots and increased dramatically in vp14. The increased ROS levels in vp14 were prevented when ABA was restored to the wild-type level by exogenous application. The effect of ABA-deficiency on ROS levels occurred specifically in the region 1-3 mm from the root apex where cell elongation is normally maintained under water deficits but is inhibited by ABA deficiency.  Imaging with the dye propidium iodide (PI), which labels cell nuclei only when plasma membrane properties are compromised, indicated that loss of plasma membrane integrity occurred in the same region of the ABA-deficient roots. This effect was also prevented by restoring ABA to the wild-type level. To reveal the sequence of increase in ROS and breach in plasma membrane integrity, we simultaneously analyzed ROS levels and PI staining in individual cells during time course experiments. The results indicate that increase in ROS levels preceded and caused the loss of plasma membrane integrity.  The relation of these events to the inhibition of root elongation caused by ABA-deficiency under water deficits is under investigation.

 

 

Drought adaptation in maize, wheat and soybean: some signalling aspects

 

Christian R. Jensen and Fulai Liu

 

The Royal Veterinary and Agricultural University, Department of Agricultural Sciences,  Hoejbakkegaard Alle, DK-2630 Taastrup, Denmark

 

Abstract:  The root system communicates changes in soil water availability to the shoot via xylem hydrostatic pressure and non-hydraulic (chemical composition of the xylem sap) signals. Due to a decrease in nitrate uptake by mass flow during mild drought stress, expansion growth of young leaves may decrease through changes in the cell wall protein metabolism. Also reduced nitrate uptake may immediately increase xylem pH, decreasing both the protonation of ABA and the cell wall biochemistry of the growing cells. Thus increased xylem pH may act as a drought signal reducing leaf elongation rate via an abscisic acid (ABA) dependent mechanism. Similarly there is a wealth of evidence for drought induced non-hydraulic root-to-shoot communication via increase in xylem [ABA] regulating stomatal aperture.  In field grown maize a chain of signals may eventually lead to stomatal closure and leaf surface reduction through interactive effects of reduced nitrogen supply and changes in the levels of plant growth regulators under drought. We suggest similar regulation may occur in field grown wheat for crops dependent on inorganic nitrate uptake, early decrease of nitrate uptake by mass flow is seemingly a major regulating signal. However, similar signal events may be different in soybean fixing atmospheric nitrogen by association with Rhizobium japonicum. In potted soybeans, stomatal closure during moderate soil drying is primarily induced by xylem-borne ABA, while reduction of leaf expansion under severe stress may be regulated by both hydraulic (leaf turgor) and non-hydraulic (leaf ABA concentration) signals.  In addition, a drought-induced increase in xylem ABA could be transported to the flowers and pods and act as signals controlling reproductive development. A role of ABA in inducing pod abortion in drought-stressed soybeans is proposed.

 

 

Physiology of abscisic acid (ABA) in roots under stress

 

Wolfram Hartung

 

Julius von Sachs Institut für Biowissenschaften der Universität, Lehrstuhl Botanik I,

Julius von Sachs Platz 2, D 97082 Würzburg, Germany

 

Abstract.  Abscisic acid (ABA) in roots originates from internal (biosynthesis in roots, delivery from the shoot in the phloem) and from external sources (soil solution). Environmental stress, as it is typical for soils of extreme habitats (water shortage, high salinity, alkalinity, nutrient deficiency, mechanical impedance) increases the accumulation of ABA and ABA-conjugates (predominantly ABA glucose ester) in roots. For roots this extra ABA can act as a stress hormone, inducing processes that help the roots to cope with the stress situation. This includes stimulation of root development under stress, induction of drought tolerance and stimulation of the root hydraulic conductivity.

ABA that accumulates under stress conditions also can act as a root-to-shoot stress signal, regulating the stomatal conductance and leaf development. The radial transport of ABA through the roots is important for the development of the intensity of the stress signal in the xylem. Here the apoplastic transport barriers, endodermis and exodermis and the apoplastic pH in the root cortex play an important role. The research of the last 15 years on the root stress physiology and long distance signalling of ABA has helped to improve the management of crops in arid and semi arid climates.

 

The assimilate partitioning in non domesticated rice in a water-stressed environment

 

P. K .Mohapatra

 

School of Life Science, Sambalpur University, Jyoti vihar, Sambalpur 768019, India

 

 

Abstract.  Tillering behaviour and  growth, development and assimilate partitioning to reproductive parts of different tillers of two non-domesticated rices, namely, Oryza nivara L. and Oryza rufipogon Griff. in different natural habitats were compared with that in cement pots during the wet season of 2002. The purpose of the experiment was to distinguish the effect of environment from genotypic limitation in wild species of cultivated rice. Oryza nivara is a native of dryland habitats and mono tillering in contrast to the multi-tillering Oryza rufipogon that grows in deep-water habitats. Both the species tillered profusely under favourable growth conditions. However, there was no change in the hierarchical pattern of tiller development among the tillers. A strong apical dominance was observed in assimilate partitioning, growth and development between the tillers and the order of dominance increased in an acropetal succession from base upwards. The late-formed tillers were mostly unproductive and possessed a low concentration of carbohydrates in the panicle compared to those formed earlier. Similarly, formation of large numbers of ear bearing tillers in the pot conditions was due to increased capacity for biomass production and provision of assimilates to reproductive structures. It is concluded that the tillering capacity of the species is largely dependent on environmental factors and not genotypic factors.

 

 

Adapting woody perennial systems to water-limited Mediterranean-type environments: a phase farming approach

 

                                                  

Richard HarperA,B, Nicole RobinsonA and Keith SmettemB,C

 

A Forest Products Commission, Locked Bag 888, Perth Business Centre, Perth, WA. Australia 6849 richardh@fpc.wa.gov.au

B CRC Plant Based Management of Dryland Salinity, Nedlands, WA. Australia. 6907

C Centre for Water Research, The University of Western Australia, Nedlands, WA. Australia. 6907

 

Abstract. The salinization of land and water resources is a major environmental problem in Australia, with up to 17 Mha of farmland likely to be affected. This hydrologic imbalance has been caused by the replacement of deep-rooted natural vegetation by shallow-rooted agricultural plants, and reforestation is thus required. Salinity is a cyclical feature in these landscapes, with expansion and recovery in response to climate change and subsequent revegetation. The hydrologic effects of trees in these dryland-farming systems, however, are often localized, and belts of trees can compete with crops. Dispersal of trees across paddocks interferes with crop production. Another approach is to insert short rotations (3-5 years) of trees into existing agricultural systems on a 20-25 year cycle. The premise is that the trees will rapidly de-water soil profiles to several meters depth and thus create a buffer of dry soil, with this being refilled during the subsequent agricultural phase. This is analogous to phase farming systems with perennial legumes such as Lucerne (Medicago sativa), differing in terms of likely rates of water use and depth of soil water depletion. We investigated this premise in three ways: Modelling, with this suggesting that the system may work in the deep (>10 m) soil profiles, that are common in south-western Australia, but not in areas with free water tables or deep sandy soils with high rates of recharge. Examination of 15 existing Eucalypt plantings across south-western Australia. There was evidence of soil water depletion to 10 m depth after 7 years, across a range of soil conditions. Field experimentation, on land normally used for cereal production near Corrigin, WA (300 mm/year annual rainfall). Here we manipulated tree species (Eucalyptus globulus, E. occidentalis, Acacia celastrifolia, Pinus radiata and Allocasuarina huegeliana, planting density (500, 1000, 2000 and 4000 trees/ha) and fertility to determine (a) if the premise of soil water depletion to depths of several metres in 3-4 years was possible, and (b) if it is feasible to accelerate the rate of water depletion, and hence decrease the duration of the forestry phase. Soil water beneath E. occidentalis at 4000 trees/ha was depleted to 6.5 m depth after 34 months.This paper discusses these promising results, and the technical and economic issues that need resolution before this farming system can be introduced in southern Australia.


 

 

 

Salt and drought tolerance in Eucalyptus spp.: the role of cyclitols as osmolytes

 

Mark AdamsA and Andrew MerchantB

ACentre of Excellence in Natural Resource Management, UWA, Crawley 6008, WA

BSchool of Forest Ecosystem Science, The University of Melbourne, Water St., Creswick 3363, Vic

 

Abstract.  The maintenance of leaf turgor in the face of drought and salinity is one of the most iconic of physiological phenomena exhibited by many species of eucalypt.  Both osmotic adjustment through accumulation of internal solutes and adjustment of tissue elasticity have been experimentally supported  (e.g. White, Turner & Galbraith 2000, Tree Physiology 20, 1157 – 1165) as probable mechanisms.  Despite their obvious importance, we have scant knowledge of the identity of solutes that contribute to osmotic potential in eucalypts generally and even less knowledge of those solutes that can accumulate without causing damage to physiological processes or membrane integrity (also known as compatible solutes or osmotica). From a reasonable field of candidate solutes, we have recently discovered that cyclic polyols or cyclitols are by far the most prevalent stable and cytoplasmically compatible osmotica in eucalypts. The exact identity of the cyclitol(s) involved varies among species and, interestingly, in accordance with eucalypt taxonomy. Here we illustrate the quantitative response of these solutes to drought and salinity in a number of eucalypts. Depending on species, eucalypts may display both high constitutive cyclitol concentrations and strong increases in concentration under drought and salinity stress. These patterns are briefly discussed in relation to the world literature for eucalypts and trees in general.

 

How do plants respond to spatial and temporal variations in soil water limitations?

 

Stephen Burgess,

 

School of Plant Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009

 

Abstract. During the drought period that characterises a Mediterranean-type climate, soil water limitations exhibit a temporal and spatial progression in intensity.  Shallow soil layers dry first, since they are most prone to evaporation and contain the greatest density of water-absorbing plant roots.  Deeper layers remain moist for longer since they are not subject to direct evaporation, contain less plant roots and, where groundwater is present, receive moisture inputs via capillary rise. In addition to vertical differences in water deficits, horizontal variation that may be present due to variable infiltration will intensify as the season progress.  This will depend on the location of plant roots, patches bare soil, etc. Given that soil water limitations vary horizontally, vertically and temporally, which of these variable conditions are relevant to plant growth and survival?  Do plants have the ‘luxury’ of equilibrating with the wettest soil?  Can they remain hydraulically decoupled from desiccated layers or patches?  What is the ideal root distribution to maximize water extraction from the whole root zone? I will review our current understanding of how and where roots absorb, redistribute and exude water in the rhizosphere in terms of source-sink relationships, transport pathways and transport capacities.  I will explore the physiological implications of these processes in terms of internal competition for water by plant tissues and the ecological implications in terms of plant-plant competition for soil water.

 

 

Relations between leaf d13C, tree ring growth and precipitation of Eucalyptus along a rainfall gradient between southwestern Australia and central Australia

 

Ernst-Detlef SchulzeA, Neil C. TurnerB, Dean NicolleC

 

A Max-Planck Institute for Biogeochemistry, Box 100164, 07701 Jena, Germany

B CSIRO Plant Industry, Private Bag 5, Wembley, WA 6913, Australia

C Botanical Institute, University of Adelaide, Australia

 

 

Abstract.  Eucalyptus species were collected along a rainfall gradient on the coast of Western Australia from Perth to Denmark, and along a transect from Denmark to Uluru (Ayers Rock). The collection encompassed 64 species of Eucalypus. Most of these were collected at several locations along the rainfall gradient. The d13C, specific leaf area and nitrogen concentration of leaves was measured and wood samples were taken for an assessment of tree ring growth and measurement of the d13C in wood during growth. The original hypothesis was that d13C would decrease linearly with precipitation. This hypothesis was not supported by the data. For a broad range of rainfall between 1200 mm and about 300 mm, d13C of a given species remained almost constant. Responses were variable in the low rainfall range, with some species showing a decrease in d13C with rainfall, others showing increases in d13C with rainfall and still others having a constant d13C with rainfall. An analysis of the specific site conditions should reveal the causes for these divergent responses. The analysis of tree rings proved difficult. However, it became apparent that the d13C of tree rings varies with sporadic rain events as well as a complicated pattern of stomatal closure and carbohydrate re-allocation during periods of drought. We conclude that species specific traits are important in understanding the response of Eucalyptus to drought, and that the species diversity of the genus Eucalyptus may be seen as a response to the d13C with rainfall overall climatic gradient in Australia as well as the large within-season and year-to-year variability in rainfall.

 

 

Adaptation of olive (Olea europaea L.) to water-limited Mediterranean environments

 

David Connor

 

Departamento de Agronomía, Universidad de Córdoba and Instituto de Agricultura Sostenible (CSIC), Apartado 4084, 14080 Córdoba, Spain

Abstract.  Olive has been widely grown in the Mediterranean Region for over 3000 years where the wide range of germplasm now displays considerable resistance to water shortage, to salinity, and despite subtropical origins, to low temperature also. Productivity and survival of this long-lived perennial in environments of low and variable rainfall depend on phenological and physiological characteristics but also on management. Phenological characteristics relate to time and duration of flowering and the extended period of fruit filling. Physiological ability relates to capacity to explore soil and extract water, to control water loss by transpiration, and to withstand intense internal water deficit. Critical aspects of management that maintain, albeit limited, transpiration and metabolic activity during hot dry summer months are directed at both crop and understorey. Strategic decisions are selection of cultivar, tree density, and canopy size together with understorey management by tillage, mowing, or herbicides.  Tactical adjustments are seen in extra pruning and timing of understorey operations, especially following dry winters.   New olive production in the Mediterranean and elsewhere deviates widely from traditional practice. Growers now seek higher yields and lower costs. Fewer cultivars are grown. Orchards are at higher density and the form of trees has changed to suit mechanical harvesting and pruning.  Irrigation is expanding and is often practiced at sub-optimal levels to obtain the best performance from limited water supply.  Understanding of the environmental adaptation and water relations of the crop, mostly obtained from a wide range of cultivars in traditional systems, has limited applicability to the new production systems now extending widely outside the Mediterranean Region, including in Australia.

 

Drying and wetting of soils stimulates decomposition and

carbon dioxide emission: the “Birch Effect”

 

Paul G. Jarvis, Ana Rey, Mark B. Rayment

 

Institute of Atmospheric and Environmental Science, School of GeoSciences,

The University of Edinburgh, The King’s Buildings, Mayfield Road,

Edinburgh, EH9 3JU, Scotland, U.K.

 

Abstract.  Recent work on the carbon budget of forests has revived interest in a phenomenon first characterised on agricultural soils in the 1960s by H. F. Birch in East Africa and at Rothamsted Experiment Station, and now often referred to as the “Birch Effect”. When soils become dry in the field because of lack of rain, as is common in Mediterranean climates, or are dried in the laboratory in controlled conditions, and then subsequently rewetted by precipitation or artificial addition, there is a sudden ‘burst’ of decomposition and CO2 release. Evidence from recent work using eddy covariance methodology in forests in Mediterranean regions will be used to show that this burst of CO2 release from the soil contributes significantly to reduce the net carbon gain of forests during the summer.  Evidence from recent laboratory incubations of soils at controlled temperature and water content using head-space analysis will be used to characterise the magnitude of the ‘burst’ of CO2 release in relation to these prior variables. A simple empirical model based on the laboratory incubations will be used to demonstrate that the amount of carbon lost as a result of the ‘burst’ of CO2 emission can be predicted adequately from knowledge of the soil temperature and the precipitation regimes. The contribution of carbon lost in this way to the annual carbon budget will be evaluated for one or more sites.

 

 

Drought resistance of native and introduced perennial grasses of southeastern Australia

 

T.BolgerA, A.R. RivelliA,B, and D.L. GardenC

 

ACSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601

BDepartment of Plant Production, University of Basilicata, Potenza, Italy

CNSW Agriculture, GPO Box 1600, Canberra, ACT 2601

 

 

Abstract. Perennial grasses are the key to the economic and environmental sustainability of pastures for livestock grazing on the New South Wales tablelands.  Catastrophic losses of perennial grasses can occur during drought periods and there is anecdotal evidence of differences in drought resistance among species, but information on the basic ecophysiological responses of these species to water stress is lacking.  Perennial plant characteristics and responses to water stress seem to coincide so as to comprise alternative strategies of avoidance or tolerance of tissue water deficits.  Our aim was to determine the responses of 8 perennial grass species to drought in terms of their strategy as avoiders or tolerators of water deficits.  The experiment was conducted in a growth cabinet controlled to 24 oC day/18 oC night, and a 16 h photoperiod of 600 μmol m-2s-1 photosynthetically active radiation. Plants were grown in pots containing 6.5 kg of a silty loam topsoil from Sutton, NSW.  All species showed good drought resistance, and the varied responses were interpreted in the context of the dominant strategy utilised by each species: tissue dehydration avoidance or dehydration tolerance. We conclude that species with the dehydration tolerance strategy such as Eragrostis curvula, Themeda australis and Austrodanthonia racemosa will be the most drought resistant.


 

 

 

The nitrogen nutrition status of grasslands under water deficits

 

 

Jean-Louis Durant, Victoria Gonzalez Dugo, François Gastal

 

 Unité d'Ecophysiologie des Plantes Fourragères, INRA, 86 600 Lusignan, France. jldurand@lusignan.inra.fr

 

 

Abstract.  Grasslands rarely are irrigated. They are therefore systematically submitted to more or less severe water deficits. Among other mineral deficiencies, water scarcity most often also induces a reduction of the plant nitrogen nutrition status. This further reduces forage production both quantitatively and qualitatively, and it alters the N cycling in grasslands. Although identified for long, qualitatively, the interaction with nitrogen still remains difficult to take into account in a quantitative analysis of the crop physiology under water deficits. The paper first illustrates how the nitrogen status of the crop changes under water deficits. A nitrogen nutrition index (INN) was defined as the ratio of the actual N concentration of forage upon the theoretical nitrogen concentration under optimal conditions, the latter only depending on the above ground biomass. The use of INN at low biomass levels and the use of nitrogen content of leaves directly exposed to incident radiation to estimate the INN are discussed. Based on recent field and controlled environment experiments, the paper further deals with three processes involved in the interaction: (i) the reduction of lateral water flux toward roots in top soil layers, which restrains the nitrogen availability at the soil/root interface, (ii) the response of the distribution of roots in soil, and. (iii) the direct response of the root N uptake at low soil water potential. To determine the importance of the latter process, a split root experiment on three grass species grown in nutrient solutions was conducted. When half of roots of the plants were grown in low osmotic pressure solution without nitrogen and the other half in high nitrogen (NO3-NH4+) and high osmotic pressure solution (PEG 6000) for 8 days, Festuca arundinacea and Lolium multiflorum both exhibited a reduction of their nitrogen status, whereas the nitrogen status of Dactylis glomerata remained optimum. These inter-specific differences were consistent with field observations, so far explained only by different architectures of the root systems. This suggests that the sensitivity of the root N absorption to the solution water potential might also be important.  Finally, the synthesis of these results at the whole crop production level is discussed.

 

Simulating water stress responses in crop phenology models

 

Gregory S. McMaster

 

USDA-ARS, Great Plains Systems Research Unit, 2150 Centre Ave., Bldg. D, Suite 200, Fort Collins, Colorado, U.S.A.

 

Abstract.  Understanding and predicting crop phenology is fundamental to crop management. While temperature is usually the critical environmental factor driving phenology, other factors (particularly water) can play a secondary role. Quantifying water stress responses has received less attention than temperature. This paper describes the status of a model for predicting crop phenology (Phenology MMS) that can be used independently or incorporated into existing crop growth models. This new model synthesizes and quantifies the entire developmental sequence of the shoot apex of many crops, making this information readily available to users with limited knowledge of phenology or the crop of interest.

A Java-based interface allows the user to interact with the underlying Fortran simulation model. Developmental sequences are quantified using thermal time (either growing degree-days or number of leaves.  The user chooses default values for a cultivar or changes the values as desired.  Stress responses are most simply incorporated by selecting for either optimal or stressed conditions that changes the thermal time estimates appropriately. Greater refinement of thermal estimates is possible when more information is available. It is also important to understand the effects of specific stresses on specific growth stages or developmental processes. Based on previous research, wheat and barley phenological responses have been quantified where water stress prior to jointing has little effect, and the effect increases progressively for later growth stages reaching a maximum for grain filling duration. For maize, a critical effect of water stress is on increasing the anthesis-silking thermal time interval.

 
 
Environmental and genetic control of morphogenesis in crops: towards models simulating phenotypic plasticity
 

Michael DingkuhnA D LuquetA, B QuilotB

A CIRAD/AMIS/Ecotrop, Avenue Agropolis, Lavalette, 34398 Montpellier, France

B INRA Avignon, Unité de recherche Plantes et systèmes de culture horticoles, Montfavet, France

 

 

Abstract.  As molecular biologists are realising the importance of physiology in understanding functional genomics of quantitative traits, such as those related to agronomic characters; and as physiologists are realising the formidable prospects for improving their phenotypic models with information on the underlying gene networks, researchers worldwide are working on linked physiological-genetic models. These efforts are in their early methodological stage despite/because of the availability of many different types of models, the problem being to bring together vastly different ways scientists see the plant. This paper describes exemplarily some current efforts to adapt phenotype models to the objective of simulating gene-phene processes at the plant or crop scale. Particular emphasis is given to the models’ capacity to simulate genotype x environment interaction and the resulting phenotypic plasticity, assuming that this permits defining model parameters that are closer to specific gene action. Three different types of approaches are presented: (1) a generic, mathematical-architectural model called GREENLAB that simulates resource modulated morphogenesis, (2) an ecophysiological model of peach tree fruit development and filling, parameterised for a mapping population to evaluate the potential of plugging QTL effects into the model, and (3) a new modelling concept that aims at constructing the plant and its phenotypic plasticity from meristem behaviour, with the principal hypothesis being that resource limitations and stresses feed back on the meristems. This latter choice is based on the fact that gene expression happens to a large extent in the meristems. The different modelling concepts are critically discussed with respect to their ability to simulate phenotypic plasticity and to operate with parameters that approximate specific gene action, particularly in the area of morphogenesis.

 
 
Policy issues impacting on crop production in water limiting environments

 

John C Radcliffe

 

CSIRO, Private Bag 2, Glen Osmond SA 5064

 

At the beginning of the 20th century when Australia’s Constitution was drafted, there was no perception that the Federal Government had a role in the management of Australia’s natural resources or its production systems. But over the past century, a complex of Commonwealth and State regulations and guidelines, along with additional purchaser expectations, have increasingly impacted on producers

 

The Australian Federal Government has responsibilities under its external powers for any issues of an international nature. However, the development of international treaties and agreements covering such issues as Biological Diversity, Conservation of Natural and Cultural Heritage, Migratory Routes for Birds, Conservation of Plant Genetic Resources, UNCED (Agenda 21), the Kyoto Declaration, the Convention on Persistent Organic Pollutants, together with membership of the World Trade Organisation, International Trade Agreements, maintenance of national security and the Trade Practices Act have all brought the Commonwealth closer to natural resource management and production issues at farm level.

 

The States have introduced additional, sometimes complementary regulations and guidelines covering many specific issues such as conservation of native vegetation, water resources, management of pests and diseases, waste management and pollution control for use of land, water and the atmosphere, occupational health and safety, and food quality. Markets are increasingly setting more specific purchasing standards outside of formal government frameworks, and constitute a further form of de facto regulation.

How these regulations, guidelines and standards have been developed and imposed is outlined.

 

 

Grower investigations to improve the viability of risk-prone crops in low rainfall environments of the central wheatbelt of Western Australia

 

Jeff RussellA and Angie RoeB

 

ACentre for Cropping Systems, Department of Agriculture, Western Australia, 12 York Road, Northam, Western Australia 6401

BFarm Focus Consultants, PO Box 321, Northam, Western Australia, 6401

 

 

Abstract.  Lupin and canola crops are recognised by growers in the low rainfall central wheatbelt of Western Australia as having a greater risk of failure than that of their mainstay cereal crops - wheat and barley.  However, the value of these crops is recognised for their strategic use for disease and weed breaks in cereal cropping.  In order to minimise the risk of crop failure in lupins and canola growers in the Kellerberrin district have been tackling a number of crop establishment issues to best ensure crop success in their environment.  Developments in tillage technology in the last decade have enabled growers to examine crop row spacing and seeding rate interactions with greater precision.  Manipulation of these factors is seen as a way growers can have some influence in drought proofing the crop in the event of a poor season occurring.

Crop orientation has currently become of interest to the growers with the recent developments being generated through ‘Tramline’ technology systems.  Crop architecture as impacted by seeding rate and row spacing may influence crop performance.  The concern here is if row orientation influences crop performance as this will have a bearing in the direction of establishing tramlines.  This needs consideration when a grower is planning long term farming system changes.

The results of a number of on farm research (OFR) activities conducted by members of the group in 2001 to 2003 are outlined to show how growers are best tackling the issue of reducing total crop failure in lupins and canola.  These investigations are showing that where lupin yield potential is low, as in this environment, wider than normal row spacings employed at seeding are improving yields.  The reverse is indicated with canola.  Likewise in an environment of lower yield potential, growers are refining current small scale research developments through OFR to determine the optimum seeding rate of these crops.  Results are indicating adopting lower seeding rates than those determined through the intensive research studies of agronomists.  Row orientation in lupins is less conclusive in its findings through similar OFR activities and there is the indication that this may be influenced by crop yield potential.  Decision support systems for growers are then being developed from the outcomes of the OFR carried out by group members.


 

 

New wheat performance in coastal sandplain and inland mallee environments

 

Mohammad Amjad A, Ben CurtisB and Wal K AndersonC

 

A, B Western Australian Department of Agriculture, Melijinup Road, Esperance, Western Australia 6450

C Western Australian Department of Agriculture, 444 Albany Highway, Albany, Western Australia 6330

 

Abstract. South coast growers are faced with a choice of new wheat varieties both from WA and the eastern states, about which there is often little relevant information available in the local environment. Agronomic investigations were carried out to identify new wheat varieties suitable for the Esperance port zone to improve yield, grain quality and local adaptation on the costal sandplain (average annual rainfall 490 mm and May-October rainfall 342 mm) and inland Mallee (average annual rainfall 342 mm and May-October rainfall 209 mm). A total of 31 wheat varieties were tested in both small-scale agronomy trials and large-scale farmers’ trials. A good start to the 2003 season followed by consistently good conditions around grain filling has generally resulted in higher grain yield averaging over 3.0 and 4.0 t/ha in the mallee and sandplain environments, respectively. May sowing on the opening rains in the Mallee resulted in 40 % greater yield than the late June sowing. On the sandplain the May sowing (in marginal conditions) yielded similar to late June sowing (3.5 t/ha), and the early June sowing out-yielded both May and late June sowing by 0.5 t/ha. Differences between varieties in response to increasing seed rate that were evident at 30kg/ha of applied N were much less evident at 60kg/ha of N. All varieties responded positively to the combination of high seed rate (200 plants/m2) and 60 kg/ha of N. Foliar disease resistance (leaf, stem and stripe rusts, and Septorias) and grain quality problems (including staining, sprouting, low falling numbers and mouldy grain) are still a great concern in the adaptation of new wheat varieties in the Esperance port zone. High yield potential and high grain quality attributes are the key parameters in variety selection on the coast. Based on the results of 2003 and field experience there appears to be a trade-off between yield, disease resistance and susceptibility to weather damage. The highest yielders have been Wyalkatchem and H45 in 2003. Wyalkatchem has broken down to stem rust and looks risky for the Esperance region.  H45 is susceptible to stripe rust and requires special management. Based on limited testing in 2003 GBA Sapphire, WAWHT2524 and WAWHT2661 have also shown promise. The best tolerance to weather damage is probably found in Sun types (Braewood) and Cook/Sunelg type (WAWHT25252A), and the disease situation is best addressed with Janz and it’s derivatives (Annuello, Mitre and Babbler). The key consideration appears to be choosing the appropriate mix of varieties depending on the risk factors, yield, and likely sowing times. A cropping program based on one, or a limited number of varieties, is less likely to succeed in the long term. Growing two or more varieties with different maturity, better disease resistance, tolerance to weather damage and grain quality characteristics should help to reduce risks in the south coast environments of Western Australia.

 

 

Responses of tomato to reduced irrigation

 

M. Hossein Behboudian, Lai F. Ow and Jorge A. Zegbe -Dominguez

Institute of Natural Resources, College of Sciences, Massey University, Palmerston North, New Zealand

 

Abstract.  Water supplies are limited worldwide and therefore there is a need to adopt water-saving irrigation practices. In a glasshouse study we compared deficit irrigation (DI) with partial rootzone drying (PRD) for their effects on ‘Petopride’ processing tomato (Lycopersicon esculentum Mill.). The treatments were: full watering on both sides of the root system considered as control (C), half of the irrigation water used in C applied to both sides of the root system at each irrigation (DI), and half of the irrigation water in C applied to only one side of the root system at each irrigation (PRD). Photosynthetic rate, transpiration rate, stomatal conductance, and leaf water potential, measured on five occasions, were lower for DI and PRD than for C. Total fruit dry and fresh mass per plant as well as harvest index was reduced in DI and PRD. Irrigation use efficiency was higher and fruit water content was lower in DI and PRD than in C. Fruit size, in terms of fresh mass, was the same for the three treatments. On a percentage basis, less dry matter in the plant was allocated to DI and PRD fruit than to C fruit. Tomato fruit, which is normally a stronger sink than vegetative parts, becomes a weaker sink during water stress. Quality was enhanced in terms of higher concentrations of sucrose, glucose and fructose in DI and PRD fruit than in C fruit. DI and PRD fruit also showed advanced ripening judged by higher production of ethylene and CO2. The earlier ripening of DI and PRD fruit was further supported by the rapid development of red colour. DI and PRD had a higher incidence of blossom end rot than did C. Differences in growth and yield were not significant between DI and PRD. Growers who are presently using DI should find little benefit in switching to PRD, as the implementation of PRD is time consuming and installation costs higher.  However, water was saved by 50% in both DI and PRD treatments and their adoption may be economically feasible in regions where water shortage could limit the production of tomatoes. 

 

Maize (Zea mays L.) and sorghum (Sorghum bicolour L.

Moench)  response to water deficit in a Mediterranean environment

 

Imma FarréA, Jose M FaciB

 

 A Department of Agriculture, Locked Bag 4 Bentley, Western Australia 6983

B Unidad de Suelos y Riegos, Centro de Investigación y Tecnología Agroalimentaria de Aragón, Apdo 727, 50080 Zaragoza, Spain

 

Abstract.  Growing more drought tolerant crops can save water in regions where irrigation water is limited. Field experiments were conducted during two growing seasons on a loam soil (Typic Xerofluvent) to compare the responses of maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) to deficit irrigation. Soil water status, crop development, yield and yield components were measured in a sprinkler line-source experiment. Seasonal evapotranspiration, crop growth, total above-ground biomass and yield were markedly affected by the irrigation treatments in both crops. Growth and yield were less in 1994 than in 1995, due to additional salt stress in 1994. Maize was superior to sorghum under well irrigated conditions, but sorghum outyielded maize under moderate or severe water deficits. In both crops yield was reduced through the reduction in the number of seeds per m-2 and seed weight. Sorghum had a greater ability to extract soil water from deeper soil and its higher yield under deficit irrigation was achieved by a higher above-ground biomass and a higher HI. Biomass and yield were linearly related to ET in both crops, with absolute greater slopes in maize. The two crops did not differ in WUE but sorghum appeared more efficient in the use of supplemental irrigation water under drought. The results show that sorghum could be an alternative crop to maize under limited water supply in the semi-arid conditions of northeast Spain.


 

 

 

Drought resistance in wild emmer wheat, a potential for wheat improvement

 

Y. SarangaA, Z. PelegA, S. AbboA, T. KrugmanB, E. NevoB, D. YakirC and T. FahimaB

 

AThe Robert H. Smith Institute of Plant Science and Genetics in Agriculture,

The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel

BInstitute of Evolution, University of Haifa, Mt. Carmel, Haifa 31905, Israel

CDepartment of Environmental Sciences and Energy Research, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel

 

 

Abstract. Wild emmer wheat (Triticum turgidum spp. dicoccoides (Körn.) Thell.), the tetraploid progenitor of cultivated wheat, is a potential source for many valuable agronomic traits.  The genetic diversity for drought resistance in wild emmer wheat and its relationship with the ecogeographical parameters of the wild emmer's collection site were studied.  A collection of 110 wild emmer accessions consisting of 25 populations collected in Israel and vicinities as well as three control durum wheat cultivars were examined under two irrigation regimes, well-watered and water-limited.

Wide genetic diversity was found both between and within the wild emmer populations in most variables under each treatment.  A considerable number of the wild emmer accessions exhibited greater total dry matter and spike dry matter under both treatments and smaller susceptibility to drought stress, as compared with their cultivated counterparts. Most wild emmer wheat accessions exhibited a greater carbon isotope ratio (δ13C, indicating higher water use efficiency) under the dry treatment and higher plasticity of δ13C (greater improvement in response to stress) relative to the cultivated controls, which may have contributed to the drought adaptation of the former.  These results suggest that wild emmer wheat may offer the potential to improve drought resistance of cultivated wheat.  The most outstanding drought resistance capacity was detected in wild emmer populations from hot, dry locations, directing further exploration to these ecosystems.

 

 

Quantitative relationship between grain and whole plant dry-matter increase during the grain-filling period in wheat subjected to postanthesis water deficit

 

Tohru Kobata and Kei Kunimasa

 

Faculty of Life and Environmental Science, Shimane University, Nisikawatu-cho, Matsue 690-8504 Japan

 

 

Abstract. Wheat crops grown in Mediterranean climatic regions often suffer terminal water stress during the grain filling period. Consequently, quantitative analysis of the effect of postanthesis water deficit on grain production may be significant in overcoming or diminishing yield reduction. A theoretical expression of grain growth based on dry matter analysis has been proposed to describe the effects of dry soils and shading during the grain filling period (GFP) of rice. This expression predicts grain dry-matter increase (G) as a function of the total shoot dry-matter increase (W) during the GFP, and is based on two parameters: potential G, and the quantity of potentially mobilized reserves in the stem. Spring wheat (Norin 61) was grown in pots under several soil moisture regimes during the GFP. Both W and G decreased with the strength of soil drying. A proportion of the severe desiccated plants were rehydrated after early GFP. The relationship between G and W was indicated by two trends: G equalled potential G when the total assimilate supply (the amount of potentially mobile reserves in the stem plus the W) was equal to, or greater than the potential G. Below that level of assimilate supply, G decreased in proportion to W during the GFP. The G of the rehydrated plants almost reached that of well-irrigated control plants. Hence we conclude that the model concept established in rice is equally applicable to wheat subjected to postanthesis water deficit during the GFP. This model can also be used as a sub-model to estimate the impact on wheat grain production of water deficit during GFP.

 

 

Boron toxicity in barley affected by pattern of boron application

 

Sui-Kwong Yau

 

Faculty of Agricultural and food Sciences, American University of Beirut, Bliss Street,

P.O. Box 11-0236, Beirut, Lebanon

 

 

Abstract. In dry areas, crops are prone to be affected by boron (B) toxicity caused by high soil B levels. In most of the studies on B toxicity in pots, excess B was introduced right from germination. Growing plants in soils uniformly mixed with B could have exaggerated the effects of B toxicity in the field, where high B levels usually occur in subsoils. The objective of this experiment was to study the effects of different patterns and timings of B supply on the development, growth, and yield of barley. The pot experiment was conducted in a plastic house. Each pot consisted of two sections of 20-cm tall PVC pipe. At a specific time, the second section was watered to field capacity and joined to the bottom of the top section. A three-factor factorial design that consisted of three patterns of B supply, three timings of B supply, and two barley lines was used with two replicates. A barley line from the cross Arar/Arabic Aswad (abbreviated as AA) and the variety ‘Harmal’ were compared. The former had less severe foliage B-toxicity symptoms than the latter in previous year's seedling test. The three patterns of B supply were: no B added (-/-), B added to the bottom section only (-/+), and B added to both sections (+/+). The addition of 50 mg B/kg soil increased the hot-water soluble B level from 0.7 to 21 p.p.m. The sections were joined on 25 Jan (tillering; roots reached the bottom of top section), 15 Feb (elongation), and 20 Mar (flag leaf emerged for Harmal; booting stage for AA). There were highly significant differences in grain yield between the three patterns of B supply [(-/-) > (-/+) >> (+/+)]. Delay in adding the second section decreased yield, but there was no interaction between the two factors. Compared to the -/- treatment, Harmal had a significant yield reduction under the -/+ treatment, but there was no yield reduction for AA. The yield difference between the two lines decreased in the +/+ treatment. Three conclusions can be drawn from the results of this study. First, subjecting plants to high B soils from germination to maturity exaggerates the effects of B on rain-fed crops in the fields. Second, high subsoil boron levels can cause yield reduction even when roots reach it as late as the boot stage. Third, the screening of seedling for severity of B-toxicity symptoms at high B levels is able to differentiate the yield responses of genotypes to high sub-soil B level.

 

Response to water deficits of lentil genotypes from West Asia, South Asia and progenies between the two sources

 

R Shrestha A, B, Neil C. Turner A, C, David W TurnerB and K H M SiddiqueA

 

A Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009

B School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

C CSIRO Plant Industry, Private Bag 5, Wembley, WA 6913

 

Abstract.  Lentil (Lens culinaris M.) is the major legume crop in Nepal occupying 59% of the area and production under grain legumes. It is mainly sown as a dry season crop during the winter months (Oct. to Mar.). Its productivity depends mainly on the amount of residual soil water from the preceding crop and having genotypes adapted to these conditions. This glasshouse study was carried out to examine the effect of different timings of water deficit on dry matter and yields of lentil genotypes of diverse origin. The three watering regimes were (i) water withheld at the late vegetative stage (72 to 93 DAS) (ii) water withheld at 50% podding (93 to maturity) and (iii) well watered control. The genotypes were Cassab, a large-seeded West Asian genotype, the South Asian cultivars Khajura 2 and Simal and crossbreds ILL 7979, ILL 7982 and ILL 6829 between West Asian and South Asian types (seed weight ranging from 1.8 to 4.3 g/100 seed). Lentil genotypes responded differently to water deficits applied either during the late vegetative stage or reproductive stage (from 50% podding). Water deficits at the late vegetative stage drastically reduced leaf area, plant height, total dry matter, flower production, pod and seed numbers, while water deficits at podding increased the numbers of flowers that dropped and the number of empty pods. Water deficits significantly reduced seed yields, by up to 60% in the crossbreds (ILL 7979, ILL 6829 and ILL 7982) and Simal, while seed yield was either not affected or increased by a water deficit at the vegetative stage in the West Asian genotype Cassab and a South Asian genotype, Khajura 2. Seed yield was closely related to flower, pod and seed numbers. The effect of a water deficit on flower numbers was highly variable, with Cassab and Khajura 2 showing more flowers after a water deficit. The genotypes ILL 7979 and Simal that had high dry matter production when well watered were the most severely affected by water deficits, particularly when applied during the late vegetative phase. In summary, water deficits substantially reduced leaf area, dry matter and flower numbers and increased flower drops, with genotypes showing significant variation in these traits with response to water deficits.

 

 

Selection strategies for enhancing drought stress tolerance in chickpea (Cicer arietinum L.)

 

S.S. YadavA, F. MuhelbauerB, Neil C. TurnerC, Bob ReddenD, P.N. BahlE, and  J. KumarA

 

ADivision of Genetics, Indian Agricultural Research Institute, New Delhi-12, India

USDA-ARS, 303 Washington State University, Pullman, Washington 99164-6434 USA.

CCSIRO Plant Industry, Private Bag 5, Wembley, WA 6913

DATFCC, Agriculture Victoria, Horsham, Victoria, Australia

EFAO, Grain Legumes Lead Consultant, New Delhi, India

 

Abstract.  Present investigations were taken up to formulate the selection strategies for screening the segregating populations and to identify drought tolerant chickpea genotypes. Three breeding populations developed separately through complex crosses, double crosses and simple crosses were advanced under rainfed environments in multiple sick-plot during 1994-01. Selection for various traits like number of branches, number of pods, seed yield, tolerance to drought and resistance against soil brome diseased was exercised in spaced planted population in each cross separately. The superior performing genotypes from complex crosses, double crosses and simple crosses were also evaluated under rainfed conditions during 2001-03. The relative performance was analyzed for various traits and results obtained showed that the general mean of different traits of new genotypes developed through complex and double crosses was significantly higher than those new genotypes developed from simple crosses and well adopted check varieties. It is interesting to mention that the yield superiority was ranging between 23 to 59 per cent, coupled with drought tolerance and resistance against Fusarium wilt. The performance in respect to number of branches, number of pods and biomass production was also observed more or less of the some patterns in these crosses. Considering these findings it was concluded that though drought stress tolerance is influenced and controlled by many environmental factors even than the effective genetic manipulations and breeding approaches can provide a very effective tool in producing drought tolerant chickpea genotypes. Based on these findings it is suggested that legumes breeder are required to develop segregating populations through complex crosses and generation advancement may be carried out under unfavorable environments or water limiting conditions.