Effects of Timing of Drought Stress on Abscission and Dry...

J. Agronomy & Crop Science 177, 327—338 (1996)©1996 Blacku'cU Wissenschafts-Verlag, BerlinISSN 0931-2250

Agronomy Division, International Crops Research Institute for the Semi-Arid Tropics (ICRIS.4T},Patancheru, Andhra Pradesh 502 324, India

Effects of Timing of Drought Stress on Abscission and Dry MatterPartitioning of Short-duration Pigeonpea

F. B. LOPEZ, Y. S. CHAUHAN and C. JOH^VNSEN

Authors' address: Dr F. B. LoPEZ, Dr Y. S. CHAUHAN and Dr C. JOHANSEN (corresponding author), InternationalCrops Research Institute for the Semi-Arid Tropics (ICRISAT) Asia Center. Patancheru, Andhra Pradesh 502 324,India.

4 figures and 4 tables

Received September 8, 1995; accepted Jidj 12, 1996

Abstract

Shoot dry mass partitioning and cumuJative abscission of leaf, flowers and pods were determined for nine short-duration pigeonpea genot^^es grown with adequate soil moisture throughout growth (control), or subjected towater stress during the late vegetative and flowering (stress 1), flowering and early pod development (stress 2), orpod fill (stress 3) growth stages. The total cumulative dry mass of abscised plant parts was lower for determinategenotypes, but it increased to a greater extent under water stress than that of indeterminate genotypes, with stress 2having the greatest and stress 3 the least effects. The dry mass contribution of pods to total abscission was < 5%,and not significantly affected by water stress, while the contnbution of leaves increased and that of flowersdecreased. Stress 3 had no significant effects on abscission dr\' mass totals or components. Reduction in shoot dr}'mass under water stress was most pronounced for genotypes in the early pod development stage, and the dr)' masscontribution of leaves generally decreased and that of pods increased under stress 1 and stress 2. With similarabscission levels, the shoot dry mass of genotype ICPL 151, was similar to, or greater than, that of hybrid ICPH 9,under stress 1 and stress 2, and the contribution of pods to shoot dr\- mass was lower for hybnd ICPH 9 under bothstress treatments. Genotypic differences in drought resistance were likely due to differences in the leaf areamaintenance during, and in the recover)' of dr\' mass and pod production following, water stress periods.

Key words: Abscission, Cajanur. pigeonpea, drought resista.nce, dry matter partitioning, sensitive stage.

Introduction

Intermittent drought can reduce growth and yieldof short-duradon pigeonpea [Cajanus cajan (L.)Millsp.] to varying extents depending on itstiming and the particular genotype (ICRISAT,1988, 1989). Establishment of the physiologicalbases for genotypic differences in droughtresponse can increase the efficiency of breedingand selection for drought tolerance, especiallywhere the degree of susceptibility to droughtvaries among growth stages, and the rate ofphenological development varies among geno-

types. In short-duradon pigeonpea, seed ^ield ispardcularly sensidve to drought during the lateflowering and early pod development stages, andreducdons in both the total shoot dry matter(TDM) and the harvest index (HI) can occur(LOPEZ et al., 1996). The maintenance of TDMand HI under water stress condidt^ns are likely tobe affected by changes in the producdon andparddoning of dr)' matter among componentplant parts, and in the abscission of leaves andreproducdve units.

For pigeonpea subjected to water stress, boththe intercepdon of solar radiadon and the

. Copyngb, acannc. Center Cod. Stat^cn,: 0931-2250/96/7705-0327$ 1 1.50/0

328 LOPEZ, CHAEHAN and JOHANSEN

efficiency of its conversion into dry matter can bereduced (HUGHES and KEATINGE, 1983).Although relatively less dry matter is partitionedinto shoots compared to roots under water stress(LOPEZ, 1986), seed yield of short-durationpigeonpea genot)pes is linearly related to theshoot dry mass at final harvest under a particularsoil moisture regime (LOPEZ et al., 1996). Periodsof water stress may infiuence the rate of pro-duction and/or abscission of component shootparts which can affect the relative capacities ofthe assimilate source (leaves) and sink (repro-ductive units), leading to changes in the TDMand/or HL

For several grain legumes, leaf area develop-ment is very susceptible to water stress (PANDEYet al., 1984; MuCHOW, 1985; HOOGENBOOM etal., 1987; HUSAIN et al., 1990), while moderatewater stress levels during reproductive growthcan increase the proportion of shoot dry matterin pods (WiEN et al., 1979; TURK and HALL,1980; O N G , 1984). For medium-duration pigeon-pea under rainfed conditions, the cumulative drymass of abscised plant matenal can exceed 2.0 tha , with leaves accounting for most of thisamount (SHELDRAKE and NAR/WANAN, 1979).The present study investigated the effects ofdrought stress timing on the abscission of leaves,flowers and pods, and the partitioning of drymatter among component shoot parts of short-duration pigeonpea.

Materials and Methods

Crop establishment

The experiment was conducted in an Alfisol (UdicRhodustalf) field at ICRISAT Center, India (17°N,78°E; 500 m elevation), with two shelters that closedautomatically to prevent rain on an experimental areaof 50 m X 25 m. The soil had a maximum plantavailable water holding capacity of 60-100 n: m. Itwas surface tilled incorporating lOOkgha" ofdiammonium phosphate, and ridges spaced at0.6 m were established. Prior soil analyses and plantgrowth tests had established that nutrient deficien-cies would be unlikely in this soil and that nadveRhi^obium were adequate to ensure optimum nodu-ladon and nitrogen fixation of pigeonpea. Seeds werehand sown on 7 July 1988, with two plant-rows(0.3 m apart) established on both sides of ridges anda spacing of 0.1 m within rows. Agronomic opera-dons were carried out as necessary for adequateprotecdon against pests, diseases and weeds. Duringthe early growth stages, the experimental plotsdepended endrely on rainfall, and no supplemental

irrigadons were given. From 52 days after sowing(DAS), the automadc rain shelters were acdvated toexclude rainfall and differendal irrigadon treatmentscommenced.

Experimental design and treatments

The experiment was laid out as a split-plot designwith four replicadons. The four drought stresstiming treatments applied in the main plots were: (a)Control - Optimum moisture (maintained near fieldcapacity) throughout the crop growth period; (b)Stress 1 — Water withheld from 52 DAS until about50% leaf abscission in genotype ICPL 87 (88 DAS);(c) Stress 2 - Water withheld from 50% flowering ofICPL 87 (78 DAS) undl about 50% leaf abscission(102 DAS); (d) Stress 3 - Water withheld from mid-podfill of ICPL 87 (110 DAS) undl harvest (133DAS). Main plots were 10.5 x 3.6 m and wereseparated from each other by a 1.2 m wide borderstrip planted to ICPL 87. Water was applied by ddpirrigadon at intervals of 2—4 days depending onsurface soil dryness in control plots. A flow meter onthe main irrigadon line indicated the amount ofwater applied on each occasion. Drought stresstreatments were applied by closing lateral irrigadonlines to specified plots.

Nine short-duradon pigeonpea genotypes (sub-plot treatments) v dth varying growth habit (I = in-determinate, D - determinate), and other (H =hybnd, E = extra-early) characterisdcs were used inthe study: (1) ICPL 87 - D; (2) ICPL 151 - D; (3)ICPL 85010 - D; (4) ICPL 85045 - I; (5) ICPL85043 - I; (6) ICPH 8 - I, H; (7) ICPH 9 - D, H; (8)ICPL 84023 - D, E; (9) ICPL 85037 - I, E. Eachsubplot consisted of 4 rows (3.5 m long) on twoadjacent ridges.

^Abscission

Two perforated plasdc trays, each 360 mm long, 260mm wide, and 45 mm deep, were kept under thecanopy in each plot of the control and stressedtreatments during the development of each stress.Abscised leaves, flowers and pods collected in thesetrays were removed each week and the dry massdetermined for each plant part. Small pods (length <20 mm) were included with the flowers. Trays werekept in control plots from the start of stress 1 untilthe dme of harvest, but were removed from stressedplots at the dme of terminadon of each stresstreatment. The cumuladvc abscission of each plantpart was determined assuming that there were nodifferences in the abscission for unstressed plotsprior to the commencement of the stress treatments.

Drought Stress and Abscission in Pigeonpea 329

Table 1. The effects of soil moisture treatments on the abscission (leaf, flower and pod; g m ") of sevenshort-duradon pigeonpea genotypes' at the end of stress 1 and stress 2

Genotype

ICPL 85043ICPL 85037ICPL 151ICPH 9ICPL 85045ICPL 87ICPH 8SE

Growth habit

IIDDIDI

Stress 1 (52-88 DAS)

Control

33.633.219.421.432.017.034.0

±4.15

Stressed

37.630.128.226.435.325.127.2

(±3.82)^

Stress 2

Control

99.095.567.576.127.567.6

115.9±7.21

(78-102 DAS)

Stressed

125.5113.695.1

103.2137.597.3

133.9(±7.08)-

Genotypes are arranged in order of increasing time to flowering^SE values in parentheses are for comparing means at the same soil moisture levelI = Indeterminate, D = Determinate

E>ry matter partitioning

Three plants were randomly selected and removed(by cutting at the base) from control and stressedplots (between 0900 and 1000 h) at the terminadonof stress 1 and stress 2. Similarly, five plants wereremoved from all plots at the time of final harvest(133 DAS), which coincided with tbe end of stress 3.Plants were transported to the laboratory in poly-ethylene bags and kept in a cold room at 5 °C untilseparadon into component plant parts (leaves,stems, flowers and pods), which was completed on

the same day for sampling at the end of stress 1 andstress 2, and over 2 days at final harvest. Dry masswas determined for leaves, stem, flowers andimmature pods after oven-drying at 80 C toconstant mass, and for mature pods after sun-dr)ingfor two weeks followed by oven-drying at 80 °C for2 days. At final harvest, an addirional category' wascreated for the new flush growth which included thenewly produced leaves and stem (both light green)and flowers.

Table 2. The total abscission, and the percentage contribution of leaves, flowers and pods for seven short-duradon pigeonpea genotypes at the end of stress 3

Genotype


Total (g m )

149.4165.6170.0177.7202.1176.8187.2±8.09

Leaf (%)

60606772677472

±1.3

Components

Flowers (%)

37372926292226

±1.7

Pods (%)

3.3

3.14.62.14.24.22.2

±0.9

^Genotypes are arranged in order of increasing time to flowering; tlieir growing habits are as indicated in

Table 1for control and stress 3 were pooled for each genotype since treatment effects were non-significant


Data analysis Two earliest flowering genotypes, ICPL 85010 andICPL 84023, produced a second flush of pods by the

Data were analysed using standard analysis of time of final harvest and were therefore omittedvariance procedure using GENSTAT software. from the analysis.

100

80

(0

oZ 60

HL 40oCO

20

SF

I

I11 rx

I

m

I

I

2fi^ 2 E ^

J

li

I

85043 85037 151 ICPH9 85045 87 ICPH8

Genotypes

Leaf (control)

Leaf (stress 1)

Flower (control)

Flower (stress 1)Fig. 1. Effects of stress 1 on the abscission (% of total) of leaves and flowers (the remainder represendngpods) at 88 days after sowing for seven short-duradon pigeonpea genotypes. Genotypes are arranged fromleft to right in order of increasing dme to 50% flowering. Standard error bars for comparisons of flowers (F)or leaves (L) at the same (S) or different (D) soil moisture levels are indicated


Results

Total abscission

At the end of stress 1 and stress 2, the totalcumulative abscission (leaf, flower and pod;g m ") in control plots was lower for determi-nate compared to indeterminate genotypes (Table

1). For control plots from the end of stress 1 (88DAS) to tbe end of stress 2 (102 DAS), there was3- to 4-fold increase in the total cumulativeabscission. Total abscission was not significantlyaffected by stress 1, but tended to increaseespecially for the determinate genot^^es. Stress 2significantly increased total abscission for all

100

80

CO

oZ 60

o"(0i2 40o

20

SFI

LFI

SL

I

CLI11

m

m11I 1111

mm

^

85043 85037 151 ICPH9 85045 87 ICPH8

Genotypes

Leaf (control)

Leaf (stress 2)

Flower (control)

Flower (stress 2)

Fie. 2. Effects of stress 2 on the abscission (% of total) of leaves anil flowers (the remainder representingpods) at 102 days after sowing for seven short-duration pigconpca genotypes. Relative time to 50%flowering of genotypes, and error bars are as indicated for Fig. 1

332

Table 3. The effectspigeonpea genot\'pes

Genot\pe

of soil moisture treatments on the shootat the end of stress 1 and stress 2

Stress 1

Control

(52-88 DAS)

Stressed

dry mass

LOPEZ,

(g plant"

CHAEHAN and JOHANSEN

) of seven short-duration

Stress 2 (78-102 DAS)

Control Stressed


17.114.116.715.216.316.721.1

11.412.211.812.312.813.918.7

±1.79 (±1.56)^

14.416.621.620.520.216.624.5

±1.85 (±1.78)^

15.111.719.813.014.49.818.6

Genotypes are arranged in order of increasing time to flowering, their growth habits are as indicated inTable 1SE values in parentheses are for comparing means at the same soil moisture level

determinate genotv'pes and for the earliest butnot for the later flowering indeterminate geno-t)pes (Table 1). Total abscission was notsignificandy affected by stress 3 for all genotypesand data were pooled for each genotype (Table2).

Abscission components

Leaves and flowers accounted for between 95%and 100% of the total dry matter abscised for allgenotypes under all soil moisture conditions, withthe remainder representing pod abscission whichwas not significantly altered by any of the waterstress treatments (Figs 1, 2; Table 2). Water stressincreased the contribution of leaves and de-creased that of flowers to total abscission forearly flowering genotypes at the end of stress 1,and for all genotypes at the end of stress 2 (Figs 1and 2). At the end of stress 3, the contribution ofleaves to total abscission was between 59% and76% and was generally lowest for the earliestflowering genotypes, with no significant effect ofthe water stress treatment (Table 2).

Shoot dry mass

Shoot dry mass was significandy reduced bystress 1 only for the earliest flowering genotype(ICPL 85043), and was least affected for thisgenotype by stress 2 (Table 3). For later floweringgenotypes (ICPH 9, ICPL 85045, ICPL 87 andICPH 8), shoot dry mass was significantly

reduced by stress 2. Genotypes ICPL 151 andICPH 9 had similar shoot dry mass for controland stressed plants at the end of stress 1, whileshoot dry mass of stressed plants was greater forICPL 151 at the end of stress 2. Shoot dry massat final harvest was largely unaffected by stress 3but was reduced in line with seed yield reductionsfor stress 1, and in addition to harvest indexreductions for stress 2 (LOPEZ et al., 1996).

Shoot dry mass partitioning

Under all soil moisture treatments, leaves, stemsand pods accounted for between 90% and 100%of the total dry mass. Water stress inducedreductions in the contribution of leaves (leafmass ratio; LMR) at the end of stress 1 weresignificant only for the determinate genotypesICPL 151 and ICPL 87 (Fig. 3), and at the end ofstress 2 for all genotypes, except ICPH 8 (Fig. 4).Tlie contribution of pods (pod mass ratio; PMR)tended to increase by water stress at the end ofstress 1 and stress 2, with the increase beingsignificant for ICPL 151 but not for ICPH 9 atthe end of stress 1 (Figs 3 and 4). Thecontribution of flowers (flower mass ratio;FMR) for these two genotypes was similarlyaffected by stress 1, but more reduced for ICPH9 under stress 2 (Figs 3 and 4). At the time offinal harvest, the PMR was reduced only by stress2 with genotype ICPL 151 being least affected,while the LMR tended to increase under bothstress 1 and stress 2 and decrease under stress 3

Drought Stress and Abscission in Pigeonpea

100333

80

COCOCO

E^ 60

ooCO

o^ 400)

o

20

IISB

SLI

ELX

ii Ii•

iV

I

\

I

85043 85037 151 ICPH9 85045 87 ICPH8

Leaf

Leaf

Genotypes

Stem [H

Stem 1

Pod (control)

Pod (Stress 1]Fig. 3. Effects of stress 1 on the shoot dry mass parridoning (% of totaJ) into leaf, stem and pod (theremainder representing flowers) at the end of stress 1 for seven short-duradon pigeonpea genot^'pes.Reladve time to 50% flowering, and error bars for comparing leaf (L), stem (S) and pod (P) are as indicatedfor Fig. 1

(Table 4). The contribution of new growth (new Discussionmass rado; NMR) at harvest tended to beincreased by stress 1 for earlier floweringgenotypes (ICPL 85043, ICPL 85037 and ICPL151), and by stress 2 for later floweringgenotypes, and reduced by stress 3 for mostgenotypes (Table 4).

timing ot drout^ht stress appbcation influ-

contribudon of various components of both theabscised plant material and the remaining (intact)shoot. At the end of stress 1 and stress 2, the


100

80

wCO

E^ 60

Oo(0

o^ 40a>o

20

m

ss

ii Iii11

I

m

85043 85037 151 ICPH9 85045 87 ICPH8

Genotypes

Leaf

Leaf

Stem

Stem

Pod (control)

Pod (Stress 2)Fig. 4. Effects of stress 2 on the shoot dry mass partitioning (% of total) into leaf, stem and pod (theremainder representing flowers) at the end of stress 2 for seven short-duradon pigeonpea genotypes.Relative time to 50% flowering, and error bars for comparing leaf (L), stem (S) and pod (P) are as indicatedfor Fig. 1

total cumulative dry mass of fallen plant materialin control plots was lower for determinatecompared to indeterminate genotypes, but in-creased to a greater extent for the determinategenotypes under water stress. Greater totalabscission in indeterminate genotypes may resultfrom continued vegetative growth during repro-

ductive development leading to greater competi-tion among developing structures, and also amore rapid remobilization of nutrients from olderleaves. Under water stress, vegetative growth ismore reduced than reproductive growth (MECK-

EL et al., 1984; O N G , 1984), so that the abscissionlevels of the detcnninate approach those of the


Table 4. Effects of soil moisture treatments on the shoot dry mass partitioning (% of total) into leaf (L),stem (S), and pod (P; the remainder representing new flush growth) at final harvest for seven short-duradonpigeonpea genot>pe*

Control Stress 1 Stress 2

L L

Stress 3

L


3544265

LSP

40444338454045

±0.8±2.0±2.7

52495056515244

(±0.8)'(±1-9)(±2.6)

38742106

37383437383741

51474854575050

27765109

47514344494052

47394646414530

343244

41464242494652

55495455474943

Genotypes are arranged in order of increasing time to flowering, their growth habits are as indicated inTable 1SE values in parentheses are for comparing means at the same soil moisture level

indeterminate genotypes, which may be lessaffected because of the reduced vegetativedemand for plant nutrients. Compared to theother water stress treatments, stress 2 had thegreatest effect on total abscission, suggesting thatthe plant may be least able to meet sink demandunder this water stress treatment.

The lack of competing sinks in semi-determi-nate compared to indeterminate soybean allows amore favorable response to water stress appliedduring reproductive growth (NEYSHABOURI andHATFIELD, 1986). In pigeonpea, both determi-nate and indeterminate genotypes can continue toaccumulate dry matter in vegetative structuresafter the start of flowering and comparable HIvalues are observed (SHELDRAKE and NARAYA-NAN, 1979; SHELDRAKE, 1984). Total abscissionlevels were high for the indeterminate hybridICPH 8, and were similar for the determinatehybrid ICPH 9, and ICPL 151, indicating thatthis parameter cannot be used to separategenotypes on the basis of drought resistance.The indeterminate genotype, ICPL 85045, hadthe highest dry mass of fallen plant material atharvest, about 200 g m~^, which is slighdy lowerthan that reported for medium-duration geno-types (SHELDRAKE and NARAYANAN, 1979).

The contribution of pods (length > 20 mm) tothe dry mass of fallen plant material was smalland not significandy affected by any of the water

stress treatments for all genotypes. Yield ofshort-duration pigeonpea under both rainfed andirrigated conditions is greatly affected by internalplant conditions existing at the time of pod setand early pod development (LOPEZ et al., 1994).In addition, the only yield component thatdecreases significantly under water stress is thenumber of pods m~~ (LOPEZ et al., 1996),suggesting that the degree of yield stabilit)^ underwater stress conditions is detemiined largelyduring pod set and early pod development. Formedium-duration pigeonpea under rainfed con-ditions, abscised pods account for only 2% of thefallen material by the time of harvest (SHEL-DRAKE and NAR/\Y/VNAN, 1979). Continued seedgrowth in soybean under water stress (MECKEL

et al., 1984) is supported by mobilization ofreserves stored in vegetative structures (WP:ST-

GATE et al., 1989), and by the preferenaalmaintenance of seed water status compared tothat of the remaining shoot (WESTGATE andGRANT, 1989).

The contribution of leaves to the total drymass of abscised plant material generally in-creased and that of flowers decreased in responseto water stress during early reproductive growth.Therefore, changes in abscission under waterstress at this stage favor a reduction in thecapacity of the source relative to that of thereproductive sink, dthough the latter may already


be in excess under conditions of adequate soilmoisture (LoPEZ et al., 1994). In pigeonpea,flower production is excessive (SHELDRAKE,1984) and production of flowers destined toabscise may represent an inefficient use of sourcecapacit)'. Reducdon in flower abscission underwater stress may be due to reduced flowerproduction, as occurs for faba bean (I Ida faba;HEBBLRTHWMTE, 1982). Stress 3 did notsignificantly influence abscission componentsfor all genotypes indicating a strong resistanceto changes in the source/reproductive sink radoduring late reproductive growth. Maintenance ofsource capacity under water stress and reductionin the imbalances between source and reproduc-tive sink sizes, possibly by reducing flowerproduction and competition from vegetativesinks, are likely to result in improved droughtresistance.

The responses of shoot dry mass of intactplants to water stress varied with the stage ofdevelopment, with the late vegetative and thepod-fill stages being comparatively unaffectedand the late flowering and early pod developmentstages more affected. In faba bean, shoot drymass has a very low sensitivity to water stressduring flowering and pod fill compared to othergrowth parameters (HUSSAIN et al., 1990), whilefor other grain legumes grown under an irrigationgradient, shoot dry mass is linearly related to theamount of water applied (PANDEY et al., 1984).The shoot dry mass was similar for genotypesICPL 151 and ICPH 9 under stress 1, but theICPL 151 had a higher dry mass at the end ofstress 2. Since the total abscission levels understress conditions were similar for these twogenotypes, genotypic differences in the droughtresponses may have been due to differences indr\' mass partitioning under stress and/or in therate of recovery after water stress was relieved. Insoybean, compensatory shoot growth rates occurduring recovery from water stress (HOOGEN-BOOM et al., 1987), and in cowpea there is rapidrecovery of shoot growth following water stressperiods in the vegetative stage (TURK and HALL,1980), with new flushes of flowering producedwhen water stress is relieved at later growthstages (TURK et al., 1980; LAVXTM, 1982).

The LMR was most affected by water stressfor two determinate genotypes at the end ofstress 1, and was least affected for an indetermi-nate genotype (ICPH 8) at the end of stress 2,suggesting that indeterminate genotypes may bebetter able to maintain LMR under water stress.

Since the contribution of leaves to total abscis-sion generally increased under the stress treat-ments, the maintenance of LMR will requirecontinued leaf production and/or reduced parti-tioning of dry mass into other shoot components.For ICPL 151, the LMR was more reduced andPMR more increased under stress 1 than for thehybrid ICPH 9. An apparent promotion of podproduction under mild water stress also occursfor other grain legumes (WiEN et al., 1979; TURKand HALL, 1980; ONG, 1984), and may be due tothe differential effects of water stress onvegetative and reproductive growth rates (ONG, "J1984).

Since the PMR and shoot dry mass weresimilar or greater for ICPL 151 compared toICPH 9 at the end of the stress treatments,differences in the yield responses to droughtwere most likely due to differences in pattern ofrecover)' after water stress was relieved. A highPMR at the end of water stress during early poddevelopment possibly inhibits production of newgrowth flushes and further pod set, whichreduces the ability for yield recovery even if soil 'moisture becomes non-limiting at later growthstages. In soybean, the shedding of distal flowersis induced by substances produced in moreproximal developing pods (HUFF and D' 'BING, \1980), while in pigeonpea, the presence ofdeveloping pods may reduce the levels ofassimilates and/or nutrients below the thresholdrequired for further pod set (SHELDRAKE, 1979,1984). At the end of stress 2, most genotypeswere in the early pod development stage, andseed yield was most affected under this waterstress treatment (LoPEZ et al., 1996). Themaintenance of source capacity (by reduced leafabscission and/or continued production) duringwater stress periods and the rapid recovery of drymass and pod production following stress duringearly pod development, may lead to improveddrought tolerance in short-duradon pigeonpea.

Acknowledgements

F. B. LOPEZ was a recipient of an ICRJSATpostdoctoral research fellowship and acknowledgesthe support and advice of Dr D. L. OSWALT of theHuman Resources Development Program. We wish tothank V. F. LOPEZ, N. VENKATARATNAM, and fieldstaff of Agronomy Division for field and laboratoryassistance, and Dr S. N. SiLIM for helpful comments onthis manuscript.


Zus ainnienf as sung

EinfluB des Einwirkungszeitpunktes vonDurrestreB auf den Abwurf und die Trocken-masseverteilung fruhreifender Taubenerbsen

Die SproBtrockenmasse-Aufteilung und daskumulative Abwerfen von Blattem, Bluten undHiilsen wurden bei 9 fruhreifen Taubenerbsen-Genotypen untersucht, wobei eine Anzucht unterangemessener Bodenfeuchdgkeit wahrend desgesamten Wachstums (KontroUe) verglichenwurde nnit WasserstreB wahrend der spatenvegetativen und Bliihphase (StreB 1), wahrendder Blute und der friihen Hiilsenentwicklungs-phase (StreB 2) und wahrend der Hiilsenfiillungs-phase (StreB 3). Die gesamte kumulativeTrockenmasse abgeworfener Pflanzenteile wargeringer bei Genotypen mit determiniertemWuchs, erhohte sich aber in einem groBerenAusmaB unter WasserstreBbedingungen als beiden indeterminierten Genotypen, wobei StreB-Gruppe 2 und StreB-Gruppe 3 die geringstenAuswirkungen zeigten. Der Trockenmasseanteilder Hiilsen am Gesamtabwurf war <5% undwurde nicht signifikant durch WasserstreBbeeinfiuBt, wahrend der Anteil der Blatterzunahm und der Anteil der Bliiten abnahm.StreBbehandlung 3 hatte keine signifikantenAuswirkungen auf den Abwurf an Gesamt-trockenmasse oder einzelner Teilen der Pflanze.Die Reduktion in der SproBtrockenmasse unterWasserstreB war deutlicher fur Genotypenwahrend der friihen Hiilsenentwicklung, wahrenddie Trockenmasseanteile der Blatter grundsatzlichabnahmen and diejenigen der Hiilsen zunahmenunter den StreBbedingungen 1 und 2. Beivergleichbaren Abwurfmengen erwies sich dieSproBtrockenmasse des Genotyps ICPL 151 alsgleich oder hoher als die der Hybride ICPH 9unter StreBbedingsungen 1 und 2; der Anteil derHiilsen an der SproBtrockenmasse war geringerbei der Hybride ICPH 9 unter beiden StreB-behandlungen. Genotypische Differenzen in derTrockenheitsresistenz sind wahrscheinlich eineFolge der Unterschiede in der Blattfiachendauerwahrend und in der Erholungs phase derTrockenmasse- und Hiilsenprodukdon, die aufWasserstreBbedingungen folgten.

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