water relations, gas exchange and growth of cool-season grain legumes in a mediterranean-type...

European Journal of Agronomy 9 (1998) 295–303

Water relations, gas exchange and growth of cool-season grainlegumes in a Mediterranean-type environment

L. Leport a,*, N.C. Turner a,b, R.J. French a,c, D. Tennant d, B.D. Thomson a,K.H.M. Siddique a,d

a Centre for Legumes in Mediterranean Agriculture, University of Western Australia, Nedlands, WA 6907, Australiab CSIRO Plant Industry, Private Bag, PO, Wembley, WA 6014, Australia

c Agriculture Western Australia, PO Box 432, Merredin, WA 6415, Australiad Agriculture Western Australia, Locked Bag No. 4, Bentley, WA 6983, Australia

Received 8 May 1998; accepted 30 July 1998

Abstract

The aim of this study was to identify the physiological characteristics which may affect the yield of six cool-seasongrain legume species grown in a water-limited Mediterranean-type climate in Western Australia. The rate of netphotosynthesis, stomatal conductance and water relations were measured from flowering to complete leaf senescencein white lupin, chickpea, faba bean, field pea, grass pea and lentil. In irrigated plants, the midday leaf water potentialwas about −0.6 MPa in all species, while the maximum rate of leaf photosynthesis was 30 mmol m−2 s−1 for chickpeaand white lupin, and below 20 mmol m−2 s−1 for the other species. With the development of water deficits, the leafwater potential in rain-fed plants decreased to about −3 MPa in chickpea and lentil and −2 MPa in the other species.Photosynthesis and stomatal conductance decreased markedly as the leaf water potential decreased below −0.9 MPain all six species, including chickpea and lentil, which showed a high degree of osmotic adjustment. Despite thesimilarity in water use, restricted to the top 40 cm of soil, and water relations characteristics, yields varied markedlyamong species. Yields were strongly correlated with early biomass production and early pod development. © 1998Elsevier Science B.V. All rights reserved.

Keywords: Drought; Grain legumes; Mediterranean environment; Photosynthesis; Water potential; Water use

1. Introduction occupies more than 60% of the rain-fed area sownto grain legumes in Australia (Siddique and Sykes,1997). However, it is poorly adapted to theCrop and pasture legumes are important compo-6.5 million ha of fine-textured, neutral-to-alkaline,nents of the sustainable legume-based agriculturalred-brown earths and the shallow duplex soilssystem in the Mediterranean-climatic region ofpresent in the Mediterranean climatic zone insouthern Australia (Siddique et al., 1993).south-western Australia (Siddique et al., 1993).Narrow-leafed lupin (Lupinus angustifolius L.)Therefore, other grain legumes are being soughtfor these soils (Siddique et al., 1993). Faba bean* Corresponding author. Tel.: +61 8 93336631;

Fax: +61 8 93878991; e-mail: [email protected] (Vicia faba L.) and field pea (Pisum sativum L.)

1161-0301/98/$ – see front matter © 1998 Elsevier Science B.V. All rights reserved.PII S1161-0301 ( 98 ) 00042-2

296 L. Leport et al. / European Journal of Agronomy 9 (1998) 295–303

have been shown to be high yielding when fungal prevail in chickpea (Morgan et al., 1991), littleosmotic adjustment was observed in narrow-leafeddiseases are managed, while chickpea (Cicer arieti-

num L.), lentil (Lens culinaris Med.) and white lupin (Turner et al., 1987). Thus, grain legumespecies appear to adopt a range of mechanisms tolupin (Lupinus albus L.) are recognized as poten-

tially profitable crops on these soils (Siddique maintain yields under terminal drought, fromdrought escape to avoidance and tolerance ofet al., 1993). In addition to these crops with

immediate potential, several grain legumes with drought.The present experiment was part of a two-yearlonger-term potential, such as grass pea (Lathyrus

sativus L.), narbon bean (Vicia narbonensis L.) and study conducted at two sites in Western Australiain 1993 and 1994, in which a wide range of cool-various Vicia species, have also been identified as

adapted to the soils and climate (Siddique and season grain legume species were compared fortheir ability to adapt to a Mediterranean-typeSykes, 1997).

Mediterranean-climatic regions are charac- environment. From the data on growth, develop-ment and yield, Thomson et al. (1997) andterized by cool wet winters and hot dry summers.

Rain-fed crops are sown in autumn and seed filling Thomson and Siddique (1997) concluded that highyields were associated with high vigour and earlyoccurs in spring as terminal water deficits develop

(Turner, 1992). The fine-textured soils to which podding. The aim of the present study was todetermine whether other factors affected yield bythese grain legumes such as faba bean, field pea,

chickpea and lentil are adapted occur primarily identifying the physiological differences amongpromising cool-season grain legume species whichwhere the growing-season rainfall is less than

250 mm. Therefore, the major constraint in these may help in understanding their adaptation andyield in low-rainfall environments. The water rela-regions is a short growing season and terminal

drought. Crops can adapt to drought using three tions, gas exchange and osmotic adjustment ofwhite lupin, chickpea, faba bean, field pea, grassdifferent strategies: escape, avoidance or tolerance,

as reviewed by Ludlow (1989). Loss and Siddique pea and lentil during terminal drought were studiedon a fine-textured, neutral-to-alkaline soil at(1994) showed that in wheat grown in this environ-

ment, drought avoidance rather than drought tol- Merredin in Western Australia in 1994, a seasonwith below-average rainfall.erance is the major feature conferring adaptation

to the environment. In faba bean, it has alreadybeen reported (Siddique et al., 1993) that droughtescape is a key characteristic for adaptation to 2. Materials and methodsMediterranean environments of Australia, mainlythrough early vigour and early pod development. White lupin (Lupinus albus L. cv. Kiev mutant),

chickpea (Cicer arietinum L. acc. T1587), fabaIn contrast to faba bean, the same authors reportedthat in narrow-leafed lupin, flowering and pod set bean (Vicia faba L. cv. Fiord), field pea (Pisum

sativum L. cv. Dundale), grass pea (Lathyrus sati-occurred when spring temperatures and soil mois-ture deficits were increasing. Turner and Henson vus L. acc. 453), and lentil (Lens culinaris Med.

cv. Digger) were grown on a red-brown earth(1989) studied narrow-leafed lupin in the sameenvironment as this study, but on coarse-textured (United States Department of Agriculture soil

classification: Calcic Haploxeralf ) at Merredin,low-pH soils, and showed that the rate of leafphotosynthesis was high when plants were ade- Western Australia (31°30∞ S, 118°12∞ E). The trial

was part of a two-year study conducted at twoquately watered, but decreased much more rapidlythan wheat when soil and plant water deficits sites in Western Australia in 1993 and 1994. The

field site, experimental design and agronomicdeveloped, leading to very low rates of leaf photo-synthesis during pod set and seed filling in lupin. details of the trial (Merredin 1994) used for this

study have been described previously by ThomsonWhile osmotic adjustment has been shown to varywith species (Turner and Jones, 1980) and to be et al. (1997). Briefly, the trial was of a randomized

block design with four replicates of each grainimportant in maintaining yields when water deficits

297L. Leport et al. / European Journal of Agronomy 9 (1998) 295–303

legume species. The crops were sown on 24 May and rain-fed plants to measure the turgidweight/dry weight ratio (TW/DW ), relative water1994 in plots 2.16 m wide (12 rows, 18 cm apart,

34 cm between plots) and 40 m long and at a content (difference between fresh weight and dryweight/difference between turgid weight and dryseeding rate which gave final plant popula-

tions, measured shortly after emergence, of weight) and osmotic potential. The fresh weightwas determined on leaves harvested around41 plants m−2 for white lupin, 45 plants m−2 for

chickpea, 36 plants m−2 for faba bean, midday, and the turgid weight on the same fullyrehydrated leaves after inserting the petiole of the38 plants m−2 for field pea, 37 plants m−2 for grass

pea, and 114 plants m−2 for lentil. Target densities leaf into freshly deionised water for 4 h in a closed,darkened, humidified chamber, and dry weightwere based on experience gained from previous

years, and followed local recommendations for after leaves were dried at 70°C for 48 h (Turner,1981). At the same time, equivalent leaves wereeach species (Thomson et al., 1997). Rainfall

during the season (May–October) was recorded at sampled and immediately frozen for osmoticpotential measurements. Osmotic potential wasthe site. A 5 m section at one end of each plot was

drip-irrigated twice weekly, commencing at flow- measured on expressed sap by vapor pressureosmometry using Wescor ( Wescor, Logan, Utah,ering and ending just before maturity. The amount

applied was equivalent to pan evaporation, corre- USA) C-52 sample chambers and a WescorHR-33T dew-point microvoltmeter. The osmoticsponding to 152 mm of water applied over a 50-day

period (Thomson et al., 1997). potential at full turgor (p100) was calculated from:The leaf water potential (Yl) of upper expanded

p100

=p×RWC,leaves was measured around solar noon(10:30–14:30 h) on clear sunny days at approxi- where RWC is the relative water content and p is

the measured osmotic potential at that RWC. Themately weekly intervals between 84 and 126 daysafter sowing (DAS) using the pressure chamber level of osmotic adjustment was estimated from

the difference in p100 between leaves from the rain-technique (Scholander et al., 1964) and followingthe precautions recommended by Turner (1988). fed and irrigated plants (Turner, 1981). Dilution

of symplastic water by apoplastic water is possibleFor the measurement of Yl in chickpea and lentil,the proximal four leaflets were removed before the when using sap expressed from frozen and thawed

tissues ( Wenkert, 1980), leading to higherleaf midrib was inserted into the pressure chamber.For field pea, the leaf remained attached to the measured osmotic potentials than in the cells

and possibly an underestimation of osmoticnode when placed in the chamber so that the sealcould be clamped against the solid part of the adjustment.

Every two weeks, plants from the rain-fed por-node. The rate of decrease of Yl with time(expressed in MPa d−1) was determined by linear tion of each plot were cut at ground level within

one 0.5 m2 quadrat, dried at 70°C and weighedregression. At the same time and on similar leavesto those measured for leaf water potential, the (Thomson and Siddique, 1997). At maturity,

plants in both the rain-fed and irrigated plots wererate of net photosynthesis and the stomatal con-ductance were measured with a portable, open cut at ground level within two 0.5 m2 quadrats,

dried at 70°C and weighed. The seeds were thengas-exchange system (Model LCA3, ADC,Hoddesdon, UK). After measurement, the part of separated and weighed. At the same time that

biomass samples were taken, soil water contentthe leaf inserted into the cuvette was placed in arapid-seal plastic bag and its area measured with was measured at 20 cm intervals from 10 to 170 cm

depths in the soil by the neutron scattering tech-an area meter (Delta-T Devices, Cambridge, UK)to allow calculation of the rate of net photosynthe- nique using a Model 503 DR CPN moisture meter

(California Pacific Nuclear, California, USA).sis and the stomatal conductance per unit leaf area(m2). Statistical analyses were performed using SAS

(SAS Institute, 1987). Means and standard errorsOn 92, 105, 119 and 126 DAS, fully expandedupper leaves were also sampled from both irrigated were calculated with the SAS MEANS procedure


and tests for differences among species and treat- 0.01–0.04 MPa d−1. Significant differences amongtreatments were observed in lentil, white lupin andments were performed using a one- and a two-way

ANOVA, respectively (SAS general linear model grass pea at 92 DAS, and in all species by 105DAS. After 112 DAS, Yl decreased belowprocedure). Significant differences (P>0.05) were

identified with the LSD test. −1.5 MPa in all species. By this time, Yl ofchickpea was decreasing at a rate of 0.2 MPa d−1,that of lentil, white lupin and grass pea by0.1 MPa d−1, and that of faba bean and field pea3. Resultsby less than 0.1 MPa d−1. By the final measure-ment on 126 DAS, the Yl values of chickpea andGrowing-season rainfall (May–October) in 1994

was 173 mm, 54 mm less than the long-term lentil were significantly the lowest (−3.3 MPa),whereas in white lupin and grass pea the valuesaverage. In the irrigated crops, Yl was between

−0.5 and −0.9 MPa throughout the growing of Yl were −2.1 to −2.3 MPa, and above−2.0 MPa in field pea and faba bean.season, and was not significantly different among

species at any sampling time (Fig. 1). At 84 DAS The mean photosynthetic rate of the irrigatedplants varied from 26 to 27 mmol CO2 m−2 s−1 in(mid-August), Yl was also about −0.7 MPa in all

the rain-fed plants, but over the next four weeks chickpea and white lupin, 19 mmol CO2 m−2 s−1in lentil to 12–15 mmol CO2 m−2 s−1 in grass pea,Yl decreased in all species at an average rate offield pea and faba bean (Fig. 1). At the same time,mean stomatal conductance varied from510 mmol m−2 s−1 in chickpea and white lupin,400 mmol m−2 s−1 in lentil to 250 mmol m−2 s−1in grass pea, field pea and faba bean (Fig. 1). At84 DAS, the rain-fed plants had rates of netphotosynthesis similar to those in the irrigatedplants in all species. By 105 DAS, five days beforepod set in grass pea and 5–10 days after thebeginning of pod set in all the other species,photosynthesis had decreased markedly to around10 mmol CO2 m−2 s−1 in chickpea and grass pea,and below 5 mmol CO2 m−2 s−1 in the otherspecies. The decrease in leaf photosynthesis paral-leled a decrease in stomatal conductance to below100 mmol m−2 s−1 in chickpea and below35 mmol m−2 s−1 in lentil, lupin and grass pea(Fig. 1). At 112 DAS, when Yl began to decreasesharply, net photosynthesis was already below5 mmol m−2 s−1 in all the rain-fed plants andremained slightly positive over the next two weeksin chickpea, white lupin and grass pea (Fig. 1). Atthis time, stomatal conductance was significantlyFig. 1. Changes with time of the midday leaf net photosyntheticlower in rain-fed crops than in irrigated crops inrate, the midday leaf stomatal conductance, and the midday

leaf water potential of six irrigated (open symbols) and six all species, with values not significantly differentrainfed (closed symbols) grain legume species grown in the field among species (Fig. 1). By 112 DAS, only 30–50%at Merredin, Western Australia, in 1994. For clarity, three of the leaves were still green in these speciesspecies are presented in A and three in B. Vertical bars denote

(Thomson and Siddique, 1997). Measurements±one standard error of the mean of 6–12 measurements, wherewere terminated on 130 DAS when all the leavesthese are greater than the size of the symbol. Arrows indicate

the time that the first pod was observed in rainfed crops. were senescent in all species.


Fig. 3. The changes with time in the above-ground biomass insix grain legume species grown under rain-fed conditions in thefield at Merredin, Western Australia, in 1994. For details ofFig. 2. The changes with time in the calculated leaf osmoticsymbols, see Fig. 1.potential at full turgor (p100) in six irrigated (open symbols) and

rainfed (closed symbols) grain legume species grown in the fieldat Merredin, Western Australia, in 1994. Vertical bars denote

respectively, but in lentil and grass pea, solute loss±one standard error of the mean of four replicates, where theseare greater than the size of the symbol. had occurred in rain-fed plants and the osmotic

adjustment had decreased to zero. The TW/DWratio measured in rain-fed plants decreased slightlyThe calculated osmotic potential at full turgor

was about −1 MPa in the irrigated crops of all in all species as the drought developed. At alltimes of measurement, the TW/DW ratio wasspecies at all times of sampling (Fig. 2) and was

not significantly different in rain-fed crops until highest in faba bean and lowest in lentil (Table 1).The biomass production of the six pulses105 DAS. By 119 DAS, osmotic adjustment, mea-

sured as the difference between the irrigated and varied markedly. In the rain-fed plots, biomassproduction increased rapidly in faba bean andrain-fed plants at full turgor, was 0.1–0.6 MPa in

all species. It was the greatest in lentil (0.6 MPa) field pea, obtaining maximum values of300–350 g m−2 (Fig. 3). Grain yields of these twoand least in white lupin, grass pea and faba bean

(0.1–0.2 MPa). In leaves collected seven days later species were greater than 100 g m−2 (Table 2). Bycontrast, white lupin and chickpea grew slowly,(126 DAS), the osmotic adjustment had increased

in chickpea and field pea to 0.6 and 0.4 MPa, with maximum biomass production of 160 and

Table 1The turgid weight/dry weight ratio at four times during pod filling in the six rainfed grain legume species grown in the field atMerredin, Western Australia, in 1994

Species Turgid weight/dry weight ratio

92 DAS 105 DAS 119 DAS 126 DAS

Lentil 5.05a 4.28a 3.62a 4.15aChickpea 5.59ab 5.08b 4.56b 4.76aField pea 6.47c 5.50b 4.79bc 4.83aGrass pea 6.33bc 5.35b 5.40c 5.90bWhite lupin 6.76c 6.33c 6.22d 6.30bcFaba bean 7.84d 6.39c 6.91d 6.98c

A separate ANOVA was performed for each date. Values with the same letter within a column are not significantly different (P>0.05).


Table 2 4. DiscussionGrain yields for the six grain legume species grown under irri-gated and rainfed conditions in the field at Merredin, Western

When the soil water supply was plentiful, sig-Australia, in 1994nificant differences in the rate of net photosynthesis

Grain yield (g m−2) and stomatal conductance among the grain legumespecies were observed. The rate of net photosynthe-

Species Irrigated Rainfedsis per unit leaf area was highest in white lupin

Faba bean 400a 135a and lowest in faba bean. In contrast to the observa-Field pea 232bc 104ab tions of Henson et al. (1990) with L. cosentinii,Lentil 276b 72bc we observed no decrease in photosynthesis withGrass pea 96d 52c

leaf age in the irrigated plants. Although thereChickpea 164cd 48cwere differences among species in leaf photosynthe-White lupin 182c 33csis and in stomatal conductance at high leaf water

An ANOVA was performed for each treatment. Values with potentials, the decrease in leaf photosynthesis andthe same letter within a column are not significantly different

conductance with the decrease in Yl was remarka-(P>0.05).bly similar in all species (Fig. 4). There was amarked decrease in the rate of net photosynthesis210 g m−2 and grain yields of 33 and 48 g m−2,and stomatal conductance when Yl was −0.8 torespectively. Lentil and grass pea showed interme-−0.9 MPa. This is very similar to the leaf waterdiate performance with a maximum biomass pro-potential at which photosynthesis decreased mark-duction of 200–240 g m−2 and grain yields ofedly in narrow-leafed lupin (L. angustifolius)52–72 g m−2. In the irrigated plots, the above-(Turner and Henson, 1989) and L. cosentiniiground biomass varied from more than(Henson et al., 1989). The rate of photosynthesis700 g m−2 in faba bean to around 400 g m−2 inat Yl above −0.8 MPa in white lupin was alsowhite lupin, and grain yield varied fromsimilar to that in other lupin species (Turner and400 g m−2 in faba bean to less than 100 g m−2 inHenson, 1989). In both narrow-leafed lupin andgrass pea (Table 2). Despite the differences amongL. cosentinii, these authors showed the rate of netspecies in biomass production and grain yield,photosynthesis decreased markedly at Yl at whichtotal water use, water use before podding andabscisic acid increased in the leaves, suggestingwater use after first pod set were not differentthat the stomata close in response to the accumula-among species (Table 3). The profile of water usetion of abscisic acid in the leaf (Turner andwith depth did not show any significant differencesHenson, 1989). Our data support their findings.among species (data not shown). The difference

The major differences among the species werebetween the wettest and the driest profiles showed(i) the variation in osmotic adjustment; (ii) thethat almost all available water was extracted from

the upper 40 cm of the soil. lower values of Yl in lentil and chickpea; and (iii)

Table 3Total, pre- and post-podding water use of six grain legume species grown under rain-fed conditions in the field at Merredin, WesternAustralia, in 1994

Total water use (mm) Pre-podding water use (mm) Post-podding water use (mm)

Faba bean 174 124 50Field pea 176 122 54Lentil 182 132 50Grass pea 176 137 39Chickpea 186 140 46White lupin 170 110 60

A separate ANOVA was performed for each measurement. Values are not significantly different within each column (P>0.05).


degree of osmotic adjustment (Turner et al., 1987).In rain-fed plants the highest TW/DW ratio wasobserved in faba bean and the lowest TW/DWratio was observed in chickpea and lentil, which isconsistent with the greater degree of osmoticadjustment in chickpea and lentil and slightosmotic adjustment in faba bean. In contrast tothe views expressed by Subbarao et al. (1995), wesuggest that osmotic adjustment, which occurredlate in the season, did not maintain active growthin chickpea and lentil because it only occurredonce rates of photosynthesis were low, leaf growthhad ceased, and very little soil moisture was avail-able for crop growth. While osmotic adjustmentappeared to have little benefit in maintaining highrates of photosynthesis, it could play a role inmaintaining positive rates of photosynthesis, albeitat a low level, at low leaf water potentials inchickpea. This maintenance of a low level ofphotosynthetic activity may be critical in providingthe energy required to maintain translocation andFig. 4. The relationships between the rate of net photosynthesisthe transfer of carbon and nitrogen from theand leaf water potential (A) and stomatal conductance and leaf

water potential (B) in the six grain legume species grown in the leaves, stem and roots to the developing seed. Infield at Merredin, Western Australia, in 1994. all species except faba bean and field pea, pod

filling occurred when the rate of leaf photosynthe-sis was reduced by half to two-thirds of that thethe ability of chickpea to maintain positive rates

of photosynthesis at values of Yl below −3.0 MPa. maximum, corresponding to assimilation ratesbelow 15 mmol CO2 m−2 s−1 in chickpea, belowIn chickpea, the maintenance of a low but positive

photosynthetic activity in the leaves is not associ- 10 mmol CO2 m−2 s−1 in white lupin and lentil,and below 5 mmol CO2 m−2 s−1 in grass pea. Thisated with a significantly higher water use of this

species. Deeper root development does not appear suggests that in this environment, the ability ofgrain legume species to store assimilates duringto be a characteristic of adaptation to drought

under the limited rainfall of our experiment as vegetative growth and remobilize them to the seedsunder drought may be important in maintainingroot growth was limited to the first 40 cm of soil,

the depth of the wetting front in this dry year. seed yield, as has already been demonstrated inwheat (Palta et al., 1994).Maintenance of a low photosynthetic activity in

chickpea may be related to its ability to adjust Despite the similarity in tissue water relationsunder well-watered conditions and the response ofosmotically in response to decreasing leaf water

potential. Osmotic adjustment has been already the six species to water deficits, the species variedconsiderably in yield under both irrigated andreported in some chickpea and field pea genotypes

subjected to water shortage (Morgan et al., 1991; rain-fed conditions (Table 2). Yields were stronglyassociated with green area index (Thomson andRodrı́guez-Maribona et al., 1992). The low leaf

water potential observed in lentil was also associ- Siddique, 1997), biomass production (Fig. 3) andearliness of podding (Fig. 1). Thomson et al.ated with a large degree of osmotic adjustment,

however, osmotic adjustment was lost by the final (1997) suggested that rapid winter growth andearly flowering and maturity are critical for highsampling when leaf photosynthesis had decreased

to zero. Within a species, there is a negative seed yields in grain legumes for low rainfall regions.In our study, the species with the lowest rates ofassociation between the TW/DW ratio and the


net photosynthesis under adequate soil moisture, to drought escape will be required if the crop is tobe grown in cool, short-season Mediterranean-i.e. faba bean and field pea, had the most rapid

leaf area development and ground cover (Thomson type environments.and Siddique, 1997) and the highest yield underrain-fed conditions, and in the case of faba beanalso had the highest yield when irrigated (Table 2). 5. ConclusionIn contrast to perceptions of faba bean as adrought-susceptible crop suitable only for long- Our results demonstrate remarkably similar

physiological responses among the six grain legumeseason Mediterranean environments, it is capableof avoiding drought and producing very high yields species of different growth habit and phenology

when subjected to water deficits. We observedin short-season Mediterranean-type environmentsprovided it is sown early in autumn (Loss and similar decreases of photosynthesis and stomatal

conductance with decrease in leaf water potentialSiddique, 1997; Mwanamwenge et al., 1998).Indeed, with this ability to escape drought, faba in all six species. There was also surprisingly little

correlation between total water use or pre- or post-bean represents an important winter crop inMediterranean climates. The species with the high- podding water use and yield. Indeed while we

reported significant variations in grain yield amongest rate of net photosynthesis per unit leaf areaunder irrigated conditions, i.e. white lupin, had a the species, no significant difference was found for

total, pre- and post-podding water use or in depthlow yield under irrigated conditions, and the lowestyield (Table 2), lowest biomass accumulation of water extraction. Likewise, there was little corre-

lation between the net photosynthetic rate per unit(Fig. 3) and slowest leaf area development underrain-fed conditions (Thomson and Siddique, leaf area or the water relations characteristics and

their ability to maintain a specific level of yield1997).Surprisingly, yields in the rain-fed plots were under drought. Yield under drought conditions

was, however, strongly correlated with early bio-not correlated with total water use, or with eitherpre-podding or post-podding water use. With fre- mass production and early flowering and pod set,

as demonstrated by Siddique et al. (1993), Thomsonquent small rainfall events during the vegetativephase, water not used in transpiration was likely and Siddique (1997) and Thomson et al. (1997).

This clearly identifies drought escape as a majorto be lost by soil evaporation (Gregory andEastham, 1996) and conservation of pre-podding contributor to drought resistance in this short-

season Mediterranean-type environment. However,water use for the post-podding phase clearly hadlittle benefit in this environment, as suggested from the maintenance of yield through drought escape is

currently not possible in species such as chickpeastudies with cereals (Turner, 1997).The results of this study strongly suggest that which fail to set pods because of cool winter–spring

temperatures. In chickpea, we suggest that charac-photosynthetic activity and its maintenance asterminal drought develops is not as critical for teristics of drought tolerance will have to be iden-

tified if this species is to be better adapted to theseyield of grain legumes as early growth and earlypod development in this short-season, water-lim- short-season Mediterranean environments.ited environment (Thomson et al., 1997). Earlygrowth and matching phenological developmentto water availability have been shown to be impor- Acknowledgmenttant in cereals (Loss and Siddique, 1994; Turnerand Whan, 1995) and appear to be equally impor- We thank B. Wallington, R. Eilers, M.D. Barr,

J.M. Aurisch, L. Maiolo and D.G. Abbott fortant in grain legumes. However, where early pod-ding is impossible due to poor seed fertilization assistance with the measurements at the field site,

and L. Young for the day-to-day running of theand pod initiation at cool temperatures, as occursin current genotypes of chickpea (Siddique et al., experiment. We are grateful to B. Deboer and Dr.

R.J.N. Emery for help with statistical analysis. We1994), alternative drought resistance mechanisms


potential of leaves in mangroves and some other plants. Proc.acknowledge M. Reader, and Drs. M. Dracup,Natl. Acad. Sci. USA 52, 119–125.J. Palta and S.P. Loss for their useful comments

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