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Effect of water stress on growth and yield of indeterminate dry-bean (Phaseolus vulgaris) cultivars
Field Crops Research, 20 (1989) 81-93
81
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of Water Stress on G r o w t h and Yield of I n d e t e r m i n a t e D r y - B e a n (Phaseolus vulgaris) Cultivars* JORGE A. ACOSTA GALLEGOS 1and JOSUE KOHASHI SHIBATA2
1Bean Program CIFAP-Durango, Apartado Postal 186, 34000 Durango, Dgo. (Mexico) 2Centro de Botanica, de Postgraduados, Chapingo (Mexico) (Accepted 12 July 1988)
ABSTRACT Acosta Gallegos, J.A. and Shibata, J.K., 1989. Effect of water stress on growth and yield of indeterminate dry-bean (Phaseolus vulgaris ) cultivars. Field Crops Res., 20: 81-93. Bean seed yields in the Mexican Plateau are heavily dependent on natural rainfall. This research was conducted to determine the effects of a water shortage applied at two different phenological stages upon the growth and seed yield of three indeterminate dry-bean cultivars. The cultivars used were: Pinto Nacional 1 (PN1), Bayo Calera (BC), and Ojo de Cabra (OC). All growth and yield-related parameters were reduced by the water-stress treatments. In 1981 and 1982, the reduction in growth and seed yield was higher when the water stress was applied during the reproductive phase (WSRP) than during the vegetative stage (WSVP). In 1981 WSRP treatment decreased seed yield 42 and 50% for BC and OC, respectively, whereas WSVP treatment reduced yield 37 and 39%. In 1982 the WSRP treatment reduced seed yields by 34, 39, and 35% for PN1, BC and OC, respectively. Yield reductions in the water stress treatments were due to a decrease in leaf-area index (LAI). Number of pods/plant was the yield component most adversely affected by the stress treatments. The use of visual score for general vigor and reduced leaf senescence, combined with an estimate of number of pods/plant at maturity, is suggested for the identification of promising stress-resistant genotypes.
INTRODUCTION
Most annual crops in temperate and subhumid zones must tolerate dry periods sometime during their life-cycle, usually at some cost to seed yield. The effect on seed yield will depend on the developmental stage at which watershortage occurs and on the intensity and duration of the shortage. In legumes, *Contribution from the Centro de InvestigacionesForestales y Agropecuarias (CIFAP) del Estado de Durango. Instituto Nacional de InvestigacionesForestales y Agropecuarias (INIFAP), Mexico.
0378-4290/89/$03.50
© 1989 Elsevier Science Publishers B.V.
82 the flowering and pod-development stages are the most sensitive to drought. In soybeans (Doss et al., 1974; Sionit and Kramer, 1977), cowpeas (Hiler et al., 1972; Turk et al., 1980), peas (Salter, 1963), snap beans (Stansell and Smittle, 1980; Bonnano and Mack, 1983), and dry beans (Robins and Domingo, 1956; Dubetz and Mahalle, 1969; Stoker, 1974; Flores-Lui, 1982) water stress during flowering has markedly increased the percentage of reproductive structures shed, reducing the number of harvestable pods, and thus limiting yield. Cell expansion is one of the first growth processes affected by water shortage (Hsiao, 1973). As a consequence, plants under severe stress are generally stunted. Leaf area, one of the main components of above-ground biomass, is also reduced by drought, due to reduced leaf-area expansion and premature senescence. This process acts as a survival tactic, reducing the rate of water use and delaying the onset of more severe stress, but is generally irreversible. However, given favorable conditions, pulses with an indeterminate growth habit, like cowpeas, soybeans, and dry beans, may late-compensate for this loss of leaf-area by producing new leaves. In Mexico, approximately half of the total area planted with beans is located in the upland central Plateau and is heavily dependent on natural rainfall. The rainy season in this area is usually from the end of June to the beginning of October, but the amount and distribution of rainfall is highly unpredictable. As a consequence, crop yields are variable and, in years of extreme water shortage, yields can be nil. In a yield trial with 18 bean cultivars at seven locations in this region, the average yield at the best location was 1878 kg/ha, while at the site with the lowest yield the average was only 222 kg/ha (Acosta Gallegos et al., 1988); rainfall during the growing season at these locations was 413 and 262 mm, respectively. The purpose of the current research was to determine the effects of a water shortage applied at two different phenological stages upon the growth and yield of three indeterminate dry-bean cultivars. MATERIALSAND METHODS Two field experiments were conducted during 1981 and 1982 at Los Llanos Experimental Station, Durango, Mexico, located 1932 m a.s.1, lat. 24°24 'N, long. 104 ° 18'W. The soil in the study area is Luvic Chernozem (Typic Argiudoll ) with 0-2% slope and a pH of 6.5; it is low in organic matter content, PeO~ and N. The soil has poor water-retention capacity and is highly erodable. Prior to the 1981 experiment, the soil moisture-release curve was determined and the soil moisture tension was correlated to soil moisture content in percentage. This information was used to establish the water treatments. The cultivars utilized in 1981 were Bayo Calera, a mid-season cultivar, and Ojo de Cabra, a full-season cultivar. Both cultivars have an indeterminate prostrate type-III growth habit (Debouck and Hidalgo, 1985), and represent
83 the growth habit of commercial cultivars in the region. A third cultivar was included in 1982: Pinto Nacional 1, a short-season cultivar with the same indeterminate growth habit as Bayo Calera and Ojo de Cabra. Water treatments were intended to be the same for all cultivars each year; however, because the three cultivars differed in phenology, the treatments were altered during the 2nd year of the experiment. Four water treatments were used to evaluate the cultivars during 1981: a well-watered treatment (control), in which the soil water potential at a depth of 30 cm was maintained above - 0.3 MPa during the whole cycle (rainfall plus furrow irrigation as needed); and three treatments in which the soil water potential at the same depth was lowered below - 1.5 MPa at specific phenological stages. These three treatments were: (1) water stress from 30 days after planting to prior to the beginning of anthesis (WSVP); (2) water stress imposed at the beginning of anthesis with a duration of 15 days (WSRP); and (3) water stress from 30 days after planting to 15 days after the beginning of anthesis (WSVR). In 1982, several changes were made to obtain water-stress treatments of similar duration and intensity for the three cultivars. Treatments control and WSRP were as in 1981, while treatment WSVP was modified to start 15 days before the beginning of anthesis. To establish this last treatment, previous knowledge of phenological behavior of the cultivars was utilized. Treatment including stress during the vegetative and reproductive phases was omitted. In both years a randomized complete-block design arranged in a split plot with four replications was utilized. Water treatments were randomized in the main plots and cultivars in the subplots. Experimental plots were of 6 rows, 4 m in length with 0.76 m between rows. Plant density for all cultivars was 9 plants/m 2. Sixty kg/ha of urea and 80 kg/ha of triple-superphosphate fertilizers were band-applied at planting. In order to exclude rain from the waterstress treatments, a set of mini rain-out shelters was constructed. During each particular stress treatment, thick transparent plastic was utilized to cover the plants at night or when rain threatened. The planting dates were 1 July and 5 July for 1981 and 1982, respectively. During the experiments, soil samples were taken weekly in all treatments to determine soil water content in the profiles at 0-30 and 30-60-cm depths. This information was used to schedule irrigation for the well-watered and stressed treatments after being released from the stress. In 1981, plant growth responses were evaluated at three phenological stages: at 45, 60 and 75 days after planting (DAP) in Bayo Calera and 55, 70 and 85 in Ojo de Cabra. The following characteristics were measured: length and number of nodes in the main stem, number of primary branches, leaf-area index (LAI), and total biomass above ground. In 1982, number of nodes in the main stem was substituted for total node number in the whole plant, and the number of branches and stem length were not recorded. In 1982, these traits were evaluated at 10, 20, 30, 40, 50, and 60 days after emergence for all cultivars. For evaluation, three plants were harvested per plot, then dried at 65 ° C for 72 h in
84
a forced-air oven. Seed yield and yield components were determined by harvesting a 2-m section of two center rows. All destructive data measurements were taken from border rows, leaving the two center rows for yield determinations.
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AUG
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Fig. 1. Rainfall (ram), potential water evaporation (ram), and minimum and maximum temperatures (°C) in Los Llanos Experimental Station, Durango, in 1981 and 1982 growing seasons. TABLE 1 A m o u n t of water in m m supplied by rain and irrigation to each treatment during the growing seasons, Durango, Mexico
Treatment*
Control WSVP+ WSRP WSVR
Cultivar Pinto Nacional I
Bayo Calera
Ojo de Cabra
1981
1982
1981
1982
1981
1982
-
389 350 331 -
444 394 346 315
399 343 367
444 359 355 270
413 387 334 -
*Treatments: Control, well-watered; W S V P , water-stress vegetative phase; W S R P , water-stress reproductive phase; and W S V R , water-stress vegetative and reproductive phases. + Modified in 1982.
85 Analyses of variance were performed for all the characteristics evaluated, and simple correlations were calculated between pairs of characteristics• Climatological data, including the amount of rain in the experimental site, was recorded on a daily basis and is shown in Fig. 1. Table I includes the amount of water received from the rains and furrow irrigation by each treatment during the growing season. RESULTS
Experiment 1981 The effect of the water treatments was significant at all phenological stages for all the characteristics studied. With the exception of length and main stem BC 400 -
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Fig. 2. Biomass (g/m 2) and LAI of two indeterminance dry-bean cultivars, Bayo Calera (BC) and Ojo de Cabra (OC), under four water treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress reproductive phase (15 days duration); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar, see text). Vertical bars represent least significant difference (P < 0.05) for the water treatments; 1981.
86 TABLE 2 Stem length (cm) and number of branches on main stem of two dry-bean cultivars under four water treatments, Durango, Mexico, 1981 Treatment*
Stem length Control WSVP WSRP WSVR Branches Control WSVP WSRP WSVR
Bayo Calera
Ojo de Cabra
45*
60
75
55
70
85
33a** 30a 32a 28a
73a 70a 46b 42b
97a 8lab 59b 57b
78a 61b 69ab 57b
133a 76b 70b 67b
142a 81b 72b 72b
5.6a 5.4a 5.7a 5.7a
7.8a 8.2a 7.4a 5.9a
8.1a 8.6a 7.5a 6.9a
10.0a 7.9b 9.0ab 7.7b
11.4a 7.7b 9.3ab 8.3b
14.7a 9.1b 10.3b 9.5b
*Number of days after planting. **Tukey'stest (P < 0.05), means followedby the same letter are not significantly different from each other. +Trestments: control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress vegetative and reproductivephases (different duration depending on cultivar, see text); WSVR, water-stress vegetative and reproductive phase.
node n u m b e r at the first phenological stage, a significant interaction of water t r e a t m e n t with cultivar was found for most of the traits evaluated. In general, in comparison to the control t r e a t m e n t , plants under t r e a t m e n t W S R P were more adversely affected by the water shortage, while those under t r e a t m e n t W S V P were less affected. Leaf-area index and biomass were the traits most adversely affected by the stress t r e a t m e n t s (Fig. 2). W h e n compared to the control t r e a t m e n t , W S V P showed a reduction in biomass of 22, 25 and 35% for the cultivar Bayo Calera in each of t he three phenological stages sampled. For Ojo de Cabra, the reduction was 50, 60 and 62%. Wi t h t r e a t m e n t W S R P , which was of similar duration in bot h cultivars, biomass reduction was 18, 51 and 49% in Bayo Calera, and 20, 65 and 57% in Ojo de Cabra. T h e response of LAI to the drought-stress imposed by the water t r e a t m e n t s was similar to t h a t shown by biomass. T h e effects of water-stress t r e a t m e n t s on stem length and number of branches are p r es en ted in Table 2. A m ar ke d decrease in stem length and n u m b e r of branches was found in the water-stress t r e a t m e n t s when compared to control t r e a t m e n t . T h e data for n u m b e r of nodes in the stem are not present ed because this trait was virtually unaffected by the t r eat m ent s. It could be due to the fact
87 TABLE 3 Seed yieldand yieldcomponentsof two dry-beancultivarsunder four water treatments, Durango, Mexico, 1981 Treatment +
Seed yield
Pods/plant
Seeds/Pod
(g/m2)
Seed weight
(g/lO0)
Bayo Calera
Control WSVP WSRP WSVR
169a* 106b 98c 81d
14.2a 10.0b 10.4b 8.8c
3.8a 3.9a 3.6b 3.4c
43.0a 41.5ab 40.4abc 39.5b
154a 94b 76c 33d
17.1a 10.4b 10.6b 6.5c
3.5a 3.3b 3.2b 3.3b
36.5a 33.5ab 36.9a 32.5b
Ojo de Cabra
Control WSVP WSRP WSVR
*Tukey's test (P < 0.05), means followedby the same letter are not significantlydifferent from each other. +Treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress reproductivephase (15 days); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar, see text). t h a t this trait was defined early during plant development before the stress treatments were applied. A highly significant difference was found in seed yield for the effect of water treatments and cultivars. No difference was observed for the interaction of water t r e a t m e n t with cultivar. Results presented in Table 3 show t h a t the seed yield of Ojo de Cabra for all water-stress treatments was lower t h a n t h a t of cultivar Bayo Calera. The effect of a 15-day water-stress period imposed at the beginning of the reproductive phase (WSRP) decreased seed yields 42 and 50% for Bayo Calera and Ojo de Cabra, respectively. In the case of t r e a t m e n t WSVP, in which the duration of the stress was different for the cultivars, the reduction in seed yield was smaller t h a n t h a t of the t r e a t m e n t WSRP, even though the duration of the former t r e a t m e n t was longer. The t r e a t m e n t WSVR was the most affected by the water stress, as expected, since the duration of this particular t r e a t m e n t included the total a m o u n t of time of the two waterstress treatments, WSVP and WSRP. In this case, the full-season cultivar Ojo de Cabra was the most adversely affected due to the longer duration of the treatment. In dry beans a loss of reproductive organs can occur even under the most favorable conditions. This loss can be of different magnitude in the same cultivar depending on the environmental conditions. In the present study, the
88 quantity of reproductive organs shed during the development of the crop under the different water treatments was not determined; however, a major shed of flowers and small pods was observed in the water-stress treatments. Without exception, the yield components were diminished by the stress treatments, and this decrease was more severe for the drought treatments with longer duration (i.e. WSVR). However, considering the duration of each water-stress treatment, the stress imposed at the beginning of the reproductive phase causes a greater decrease on the yield components. In general, the number of pods per plant was the most affected by the treatments studied (Table 3 ). In each treatment, the percentage of normal and abortive seeds and undeveloped ovules was determined in 100 pods per plot. In all treatments, including the control treatment, the percentage of seeds normally developed in the pods ranged from 72 to 78% with Bayo Calera and from 55 to 65% with Ojo de Cabra (data not shown); this suggests strong intraovary competition even under favorable conditions.
Experiment 1982 Crop growth represented by node number per plant, LAI and biomass reached maximum values between 58 and 68 DAB, during flowering (Figs. 3 and 4). For number of nodes per plant, significant differences were found only among cultivars during the first three sampling times; later, significant differences were also found for the effect of the water treatments. The effect of water stress upon this trait was visible at the end of the treatments. A relative recovery was evident for the treatment WSVP, particularly in Bayo Calera. As expected for this trait, the full-season cultivar Ojo de Cabra was highly superior to Bayo Calera and Pinto Nacional 1. The pattern of response of biomass to water treatments was very similar to that of node number per plant for all cultivars, therefore data for biomass are not shown. For LAI, no significant differences were detected for any of the sources of variation during the two first dates sampled. At the 3rd sampling time, the mid and full-season cultivars Bayo Calera and Ojo de Cabra showed significantly higher values than the early cultivar Pinto Nacional. At this time, the effect of the treatment WSVP was also evident. In general, the effect of treatment WSRP upon this trait is notable because it highly increased the rate of senecence. Treatment WSVP showed a recovery after the end of the water shortage. The three cultivars under treatment WSVP flowered and reached physiological maturity 3 days before those in the other treatments. Seed yield was significantly different for the three cultivars. The rank of the cultivars was: Pinto Nacional 1 > Bayo Calera > Ojo de Cabra, with mean yields of 176, 143 and 131 g / m 2 respectively (Table 4). In the case of the water treatments, considering the seed yield of the control as 100%, respective yields of WSVP and WSRP were as follows: 83 and 66%
89
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AFTER
DAYS
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PLANTING
Fig. 3. Number of nodes per plant of three indeterminate dry-bean cultivars,Pinto Nacional I (PN1), Bayo Calera (BC) and Ojo de Cabra (OC), under three water treatments: Control, wellwatered; W S V P , water-stress vegetative phase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration). Verticalbars represent leastsignificantdifference (P < 0.05) for the water treatments; 1982. PN1
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PLANTING
Fig. 4. LAI of three indeterminate dry-bean cultivars,Pinto Nacional I (PN1), Bayo Calera (BC) and Ojo de Cabra (OC), under three water treatments: Control, well watered; W S V P , water-stress vegetative phase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration ).Verticalbars represent leastsignificantdifference (P < 0.05) for the water treatments; 1982.
90 TABLE 4 Seed yield and yield components of three dry-bean cultivars under three water treatments, Durango, Mexico, 1982. Treatment +
Pinto Nacional 1 Control WSVP WSRP
Seed yield (g/m 2)
Pods/plant
Seeds/pod
Seed weight (g/100)
212a* 176b 140c
23.7 18.6 16.3
4.0 3.8 3.8
33.5 33.4 31.0
177a 143b 108c
18.3 12.9 12.3
3.6 3.6 3.3
40.1 10.0 38.8
162a 125b 106c
24.1 15.1 12.8
3.1 2.9 3.0
31.6 31.5 31.8
Bayo Calera Control WSVP WSRP
Ojo de Cabra Control WSVP WSRP
+ Treatment: Control, well-watered; W S V P , water-stressvegetativephase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration). *Tukey's test at P < 0.05, mean values followed by the same letterare not significantlydifferent.
in Pinto Nacional 1, 81 and 61 in Bayo Calera, and 77 and 65% in Ojo de Cabra. Thus, even though both water-stress treatments were of the same duration and intensity, the stress imposed at the beginning of the reproductive phase reduced seed yield twice as much as the reduction observed when the stress was imposed at the vegetative phase. As in 1981, the number of pods per plant was the yield component most affected by the water-stress treatments. DISCUSSION
The mid and full-season cultivars, Bayo Calera and Ojo de Cabra, showed different values than expected for harvest index (HI) under stress in 1981 (Table 5 ). These responses were in part due to the differences in duration ofphenological stages. Aspinall et al. (1964) have emphasized that "the organ which is growing most rapidly at the time of the stress is the one most affected". This relationship can actually lead to an increased HI under water stress because of strong reduction in vegetative growth (Donald and Hamblin, 1976). In 1982, all cultivars showed a decrease in HI under stress when compared to control. The early-season cultivar Pinto Nacional 1 showed a high proportion of shoot dry-matter in seeds, which indicates a higher capacity of remobilization of carbohydrates and other compounds to the developing seeds. Hall and Patel (1985)
91 TABLE 5 Modifiedharvest index* of three indeterminate dry-bean cultivars under four water treatments, Durango, Mexico Treatment +
Control WSVP WSRP WSVR
Cultivar Pinto Nacional
Bayo Calera
Ojo de Cabra
1981
1982
1981
1982
1981
1982
-
0.77 0.75 0.60 -
0.40 0.38 0.46 0.62
0.53 0.49 0.40
0.44 0.69 0.51 0.46
0.51 0.46 0.49 -
*Calculated by dividing the seed yield by the highest value for biomass among the phenological stages sampled for each cultivar and water treatment. +Treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar and season); WSRP, water stress reproductivephase (15 days duration); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar). indicated similar findings with cowpea strains selected visually for early production of mature pods. In both years, m a x i m u m values for LAI were found at the end of the stress t r e a t m e n t s in the middle of the flowering period. These results, and the fact t h a t a high positive correlation was found between this trait and seed yield, suggest t h a t the decrease in yield under stress can be related to a decrease in LAI,the latter due to reduction in growth and increased senescense. Even though indeterminate cultivars of this species can compensate for leaf senescence by new growth, it seems t h a t those cultivars showing less senescence during stress are likely to produce better yields. Therefore, as Parsons (1979) indicated, leaf senescence measured on a visual scale could be effective in the process of selection in a breeding program for drought tolerance. All stress treatments evaluated in this study reduced seed yield; however, as indicated elsewhere, the highest reduction was found when the stress was imposed at the beginning of the reproductive phase. This reduction in yield was due mainly to reduction in the number of pods per plant; similar results were found by Robins and Domingo (1956), Dubetz and Mahalle (1969), and Flores-Lui (1982). In this research, a small non-significant reduction in the number of seeds per pod and seed weight was observed. Dubetz and Mahalle (1969) and Flores-Lui (1982) indicated a decrease of these yield components only when the stress was applied late in the season during pod-filling. W i t h respect to the a m o u n t of aborted seeds and undeveloped ovules, the fact t h a t the control t r e a t m e n t showed similar values as those of the stress treatments suggests
92 that strong intra-ovary competition occurred under all evaluated treatments. This may be due to limited source in relation to the strength of the sink during the seed-filling period, or to the fact that, while carbohydrate is available, it is not effectively remobilized. Harvestable yield rather than mere plant survival is the goal in any agricultural situation involving annual seed crops. However, it is well known that cultivars which yield the best in dry years may not be the best-yielding cultivars in moist years (Parsons, 1979). In the particular case of the Mexican plateau, farmers are concerned with yield stability from year to year. In the case of this study, a strong association was found over all treatments between biomass and seed yield; this result throws some light on the fact that farmers in this area use just type-III cultivars when raising beans under rainfall conditions. It is known that this type of bean possesses a certain phenotypic plasticity by having an extended flowering period and the capability to produce new leaves in the face of drought-induced senescence. This plasticity helps them to cope with short drought periods. Moreover, type-III cultivars can produce more biomass than indeterminate type-II's and determinate type-I's (typeIV cultivars, which can produce the highest values in biomass among all types of beans, have a long growing cycle and are unadapted to the Mexican semiarid highland). Thus, it is likely that farmers prefer to grow type-III cultivars because of their morphophenological characteristics. In this study, all growth and yield-related parameters were reduced by water stress. However, the results have some implications for the breeding for droughttolerance. The possible use of visual score for leaf senescence was already mentioned, and since LAI and biomass were highly correlated to yield, it seems that these traits may be used to select for drought-tolerance under stress. A necessary step before deciding which of these traits is the most appropriate is to define their correspondent heritability values. A priori, it seems that the use of a visual score on general vigor and leaf senescense under stress, combined with a high number of pods per plant at maturity, will allow breeder's to identify promising genotypes.
REFERENCES Acosta Gallegos, J.A., Ochoa Marquez, R. and Sanchez Valdez, I., 1988. Efecto del genotipo y del ambiente en algunas caracterlsticas agronomicas del frijal de temporal. Agric. Tec. Mex., 14; 1-15. Aspinall, D., Nicholls, P.B. and May, L.H., 1964. The effect of soil moisture stress on the growth of barley. I. Vegetative development and grain yield. Aust. J. Agric. Res., 15: 729-745. Bonanno, A.R. and Mack, H.J., 1983. Yield components and pod quality of snap beans grown under differential irrigation. J. Am. Soc. Hortic. Sci., 108: 869-873. Debouck, D.G. and Hidalgo, R., 1985. Morfologiade la planta de frijol comun. In: M. Lopez, F. Fernandez and A. van Schoonhoven (Editors), Frijol: Investigacion y Produccion. CIAT, Cali. Colombia, pp. 7-41.
93
Donald, C.M. and Hamblin, J.,1976.The biologicalyieldand harvest index of cerealsas agronomic and plant breeding criteria.Adv. Agron., 28: 361-405. Doss, B.D., Pearson, R.W. and Rogers, H.T., 1974. Effects of soilwater stress at various growth stages on soybean yield.Agron. J., 66: 297-299. Dubetz, S. and Mahalle, P.S., 1969. Effect of soilwater stress on bush beans Phaseolus vulgaris L. at three stages of growth. J. Am. Soc. Hortic. Sci.,94: 479-481. Flores-Lui, L.F., 1982. Flowering, pod set,yieldand dry matter partitioningof beans (Phaseolus vulgaris L.) in response to water stress and flower and leafremoval. Ph.D. thesis,University of California,Davis, 116 pp. Hall, A.E. and Patel, P.N., 1985. Breading for resistance to drought and heat. In: S.R. Singh and K.O. Rachie (Editors), Cowpea: Research, Production and Utilization.Wiley, New York, pp. 137-151. Hiler, E.A., van Bavel, C.H., Hossain, M.M. and Jordan, W.R., 1972. Sensitivity of southern peas to plant water deficit at three growth stages. Agron. J., 64: 60-64. Hsiao, T.C., 1973. Plant responses to water stress. Annu. Rev. Plant Physiol., 24: 519-570. Parsons, L.R., 1979. Breeding for drought resistance: what plant characteristics impart resistance? Hortic. Sci., 14: 590-593. Robins, J.S. and Domingo, C.E., 1956. Moisture deficit in relation to the growth and development of dry beans. Agron. J., 48: 67-70. Salter, P.J., 1963. The effect of wet or dry soil conditions at different growth stages on the components of yield of a pea crop. J. Hortic. Sci., 38: 321-334. Sionit, N. and Kramer, P.J., 1977. Effect of water stress during different stages of growth of soybeans. Agron. J., 69: 274-278. Stansell, J.R. and Smittle, D.A., 1980. Effects of irrigation regimes on yield and water use to snap beans (Phaseolus vulgaris L.) J. Am. Soc. Hortic. Sci., 105: 869-873. Stoker, R., 1974. Effect on dwarf beans of water stress at different phases of growth. N.Z.J. Exp. Agric., 2: 13-15. Turk, J.J., Hall, A.E. and Asbell, C.W., 1980. Drought adaption of cowpea. I. Influence of drought on seed yield. Agron. J., 72: 414-420.
81
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of Water Stress on G r o w t h and Yield of I n d e t e r m i n a t e D r y - B e a n (Phaseolus vulgaris) Cultivars* JORGE A. ACOSTA GALLEGOS 1and JOSUE KOHASHI SHIBATA2
1Bean Program CIFAP-Durango, Apartado Postal 186, 34000 Durango, Dgo. (Mexico) 2Centro de Botanica, de Postgraduados, Chapingo (Mexico) (Accepted 12 July 1988)
ABSTRACT Acosta Gallegos, J.A. and Shibata, J.K., 1989. Effect of water stress on growth and yield of indeterminate dry-bean (Phaseolus vulgaris ) cultivars. Field Crops Res., 20: 81-93. Bean seed yields in the Mexican Plateau are heavily dependent on natural rainfall. This research was conducted to determine the effects of a water shortage applied at two different phenological stages upon the growth and seed yield of three indeterminate dry-bean cultivars. The cultivars used were: Pinto Nacional 1 (PN1), Bayo Calera (BC), and Ojo de Cabra (OC). All growth and yield-related parameters were reduced by the water-stress treatments. In 1981 and 1982, the reduction in growth and seed yield was higher when the water stress was applied during the reproductive phase (WSRP) than during the vegetative stage (WSVP). In 1981 WSRP treatment decreased seed yield 42 and 50% for BC and OC, respectively, whereas WSVP treatment reduced yield 37 and 39%. In 1982 the WSRP treatment reduced seed yields by 34, 39, and 35% for PN1, BC and OC, respectively. Yield reductions in the water stress treatments were due to a decrease in leaf-area index (LAI). Number of pods/plant was the yield component most adversely affected by the stress treatments. The use of visual score for general vigor and reduced leaf senescence, combined with an estimate of number of pods/plant at maturity, is suggested for the identification of promising stress-resistant genotypes.
INTRODUCTION
Most annual crops in temperate and subhumid zones must tolerate dry periods sometime during their life-cycle, usually at some cost to seed yield. The effect on seed yield will depend on the developmental stage at which watershortage occurs and on the intensity and duration of the shortage. In legumes, *Contribution from the Centro de InvestigacionesForestales y Agropecuarias (CIFAP) del Estado de Durango. Instituto Nacional de InvestigacionesForestales y Agropecuarias (INIFAP), Mexico.
0378-4290/89/$03.50
© 1989 Elsevier Science Publishers B.V.
82 the flowering and pod-development stages are the most sensitive to drought. In soybeans (Doss et al., 1974; Sionit and Kramer, 1977), cowpeas (Hiler et al., 1972; Turk et al., 1980), peas (Salter, 1963), snap beans (Stansell and Smittle, 1980; Bonnano and Mack, 1983), and dry beans (Robins and Domingo, 1956; Dubetz and Mahalle, 1969; Stoker, 1974; Flores-Lui, 1982) water stress during flowering has markedly increased the percentage of reproductive structures shed, reducing the number of harvestable pods, and thus limiting yield. Cell expansion is one of the first growth processes affected by water shortage (Hsiao, 1973). As a consequence, plants under severe stress are generally stunted. Leaf area, one of the main components of above-ground biomass, is also reduced by drought, due to reduced leaf-area expansion and premature senescence. This process acts as a survival tactic, reducing the rate of water use and delaying the onset of more severe stress, but is generally irreversible. However, given favorable conditions, pulses with an indeterminate growth habit, like cowpeas, soybeans, and dry beans, may late-compensate for this loss of leaf-area by producing new leaves. In Mexico, approximately half of the total area planted with beans is located in the upland central Plateau and is heavily dependent on natural rainfall. The rainy season in this area is usually from the end of June to the beginning of October, but the amount and distribution of rainfall is highly unpredictable. As a consequence, crop yields are variable and, in years of extreme water shortage, yields can be nil. In a yield trial with 18 bean cultivars at seven locations in this region, the average yield at the best location was 1878 kg/ha, while at the site with the lowest yield the average was only 222 kg/ha (Acosta Gallegos et al., 1988); rainfall during the growing season at these locations was 413 and 262 mm, respectively. The purpose of the current research was to determine the effects of a water shortage applied at two different phenological stages upon the growth and yield of three indeterminate dry-bean cultivars. MATERIALSAND METHODS Two field experiments were conducted during 1981 and 1982 at Los Llanos Experimental Station, Durango, Mexico, located 1932 m a.s.1, lat. 24°24 'N, long. 104 ° 18'W. The soil in the study area is Luvic Chernozem (Typic Argiudoll ) with 0-2% slope and a pH of 6.5; it is low in organic matter content, PeO~ and N. The soil has poor water-retention capacity and is highly erodable. Prior to the 1981 experiment, the soil moisture-release curve was determined and the soil moisture tension was correlated to soil moisture content in percentage. This information was used to establish the water treatments. The cultivars utilized in 1981 were Bayo Calera, a mid-season cultivar, and Ojo de Cabra, a full-season cultivar. Both cultivars have an indeterminate prostrate type-III growth habit (Debouck and Hidalgo, 1985), and represent
83 the growth habit of commercial cultivars in the region. A third cultivar was included in 1982: Pinto Nacional 1, a short-season cultivar with the same indeterminate growth habit as Bayo Calera and Ojo de Cabra. Water treatments were intended to be the same for all cultivars each year; however, because the three cultivars differed in phenology, the treatments were altered during the 2nd year of the experiment. Four water treatments were used to evaluate the cultivars during 1981: a well-watered treatment (control), in which the soil water potential at a depth of 30 cm was maintained above - 0.3 MPa during the whole cycle (rainfall plus furrow irrigation as needed); and three treatments in which the soil water potential at the same depth was lowered below - 1.5 MPa at specific phenological stages. These three treatments were: (1) water stress from 30 days after planting to prior to the beginning of anthesis (WSVP); (2) water stress imposed at the beginning of anthesis with a duration of 15 days (WSRP); and (3) water stress from 30 days after planting to 15 days after the beginning of anthesis (WSVR). In 1982, several changes were made to obtain water-stress treatments of similar duration and intensity for the three cultivars. Treatments control and WSRP were as in 1981, while treatment WSVP was modified to start 15 days before the beginning of anthesis. To establish this last treatment, previous knowledge of phenological behavior of the cultivars was utilized. Treatment including stress during the vegetative and reproductive phases was omitted. In both years a randomized complete-block design arranged in a split plot with four replications was utilized. Water treatments were randomized in the main plots and cultivars in the subplots. Experimental plots were of 6 rows, 4 m in length with 0.76 m between rows. Plant density for all cultivars was 9 plants/m 2. Sixty kg/ha of urea and 80 kg/ha of triple-superphosphate fertilizers were band-applied at planting. In order to exclude rain from the waterstress treatments, a set of mini rain-out shelters was constructed. During each particular stress treatment, thick transparent plastic was utilized to cover the plants at night or when rain threatened. The planting dates were 1 July and 5 July for 1981 and 1982, respectively. During the experiments, soil samples were taken weekly in all treatments to determine soil water content in the profiles at 0-30 and 30-60-cm depths. This information was used to schedule irrigation for the well-watered and stressed treatments after being released from the stress. In 1981, plant growth responses were evaluated at three phenological stages: at 45, 60 and 75 days after planting (DAP) in Bayo Calera and 55, 70 and 85 in Ojo de Cabra. The following characteristics were measured: length and number of nodes in the main stem, number of primary branches, leaf-area index (LAI), and total biomass above ground. In 1982, number of nodes in the main stem was substituted for total node number in the whole plant, and the number of branches and stem length were not recorded. In 1982, these traits were evaluated at 10, 20, 30, 40, 50, and 60 days after emergence for all cultivars. For evaluation, three plants were harvested per plot, then dried at 65 ° C for 72 h in
84
a forced-air oven. Seed yield and yield components were determined by harvesting a 2-m section of two center rows. All destructive data measurements were taken from border rows, leaving the two center rows for yield determinations.
35I
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JUL
AUG
SEP
OCT
Fig. 1. Rainfall (ram), potential water evaporation (ram), and minimum and maximum temperatures (°C) in Los Llanos Experimental Station, Durango, in 1981 and 1982 growing seasons. TABLE 1 A m o u n t of water in m m supplied by rain and irrigation to each treatment during the growing seasons, Durango, Mexico
Treatment*
Control WSVP+ WSRP WSVR
Cultivar Pinto Nacional I
Bayo Calera
Ojo de Cabra
1981
1982
1981
1982
1981
1982
-
389 350 331 -
444 394 346 315
399 343 367
444 359 355 270
413 387 334 -
*Treatments: Control, well-watered; W S V P , water-stress vegetative phase; W S R P , water-stress reproductive phase; and W S V R , water-stress vegetative and reproductive phases. + Modified in 1982.
85 Analyses of variance were performed for all the characteristics evaluated, and simple correlations were calculated between pairs of characteristics• Climatological data, including the amount of rain in the experimental site, was recorded on a daily basis and is shown in Fig. 1. Table I includes the amount of water received from the rains and furrow irrigation by each treatment during the growing season. RESULTS
Experiment 1981 The effect of the water treatments was significant at all phenological stages for all the characteristics studied. With the exception of length and main stem BC 400 -
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Fig. 2. Biomass (g/m 2) and LAI of two indeterminance dry-bean cultivars, Bayo Calera (BC) and Ojo de Cabra (OC), under four water treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress reproductive phase (15 days duration); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar, see text). Vertical bars represent least significant difference (P < 0.05) for the water treatments; 1981.
86 TABLE 2 Stem length (cm) and number of branches on main stem of two dry-bean cultivars under four water treatments, Durango, Mexico, 1981 Treatment*
Stem length Control WSVP WSRP WSVR Branches Control WSVP WSRP WSVR
Bayo Calera
Ojo de Cabra
45*
60
75
55
70
85
33a** 30a 32a 28a
73a 70a 46b 42b
97a 8lab 59b 57b
78a 61b 69ab 57b
133a 76b 70b 67b
142a 81b 72b 72b
5.6a 5.4a 5.7a 5.7a
7.8a 8.2a 7.4a 5.9a
8.1a 8.6a 7.5a 6.9a
10.0a 7.9b 9.0ab 7.7b
11.4a 7.7b 9.3ab 8.3b
14.7a 9.1b 10.3b 9.5b
*Number of days after planting. **Tukey'stest (P < 0.05), means followedby the same letter are not significantly different from each other. +Trestments: control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress vegetative and reproductivephases (different duration depending on cultivar, see text); WSVR, water-stress vegetative and reproductive phase.
node n u m b e r at the first phenological stage, a significant interaction of water t r e a t m e n t with cultivar was found for most of the traits evaluated. In general, in comparison to the control t r e a t m e n t , plants under t r e a t m e n t W S R P were more adversely affected by the water shortage, while those under t r e a t m e n t W S V P were less affected. Leaf-area index and biomass were the traits most adversely affected by the stress t r e a t m e n t s (Fig. 2). W h e n compared to the control t r e a t m e n t , W S V P showed a reduction in biomass of 22, 25 and 35% for the cultivar Bayo Calera in each of t he three phenological stages sampled. For Ojo de Cabra, the reduction was 50, 60 and 62%. Wi t h t r e a t m e n t W S R P , which was of similar duration in bot h cultivars, biomass reduction was 18, 51 and 49% in Bayo Calera, and 20, 65 and 57% in Ojo de Cabra. T h e response of LAI to the drought-stress imposed by the water t r e a t m e n t s was similar to t h a t shown by biomass. T h e effects of water-stress t r e a t m e n t s on stem length and number of branches are p r es en ted in Table 2. A m ar ke d decrease in stem length and n u m b e r of branches was found in the water-stress t r e a t m e n t s when compared to control t r e a t m e n t . T h e data for n u m b e r of nodes in the stem are not present ed because this trait was virtually unaffected by the t r eat m ent s. It could be due to the fact
87 TABLE 3 Seed yieldand yieldcomponentsof two dry-beancultivarsunder four water treatments, Durango, Mexico, 1981 Treatment +
Seed yield
Pods/plant
Seeds/Pod
(g/m2)
Seed weight
(g/lO0)
Bayo Calera
Control WSVP WSRP WSVR
169a* 106b 98c 81d
14.2a 10.0b 10.4b 8.8c
3.8a 3.9a 3.6b 3.4c
43.0a 41.5ab 40.4abc 39.5b
154a 94b 76c 33d
17.1a 10.4b 10.6b 6.5c
3.5a 3.3b 3.2b 3.3b
36.5a 33.5ab 36.9a 32.5b
Ojo de Cabra
Control WSVP WSRP WSVR
*Tukey's test (P < 0.05), means followedby the same letter are not significantlydifferent from each other. +Treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar, see text); WSRP, water-stress reproductivephase (15 days); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar, see text). t h a t this trait was defined early during plant development before the stress treatments were applied. A highly significant difference was found in seed yield for the effect of water treatments and cultivars. No difference was observed for the interaction of water t r e a t m e n t with cultivar. Results presented in Table 3 show t h a t the seed yield of Ojo de Cabra for all water-stress treatments was lower t h a n t h a t of cultivar Bayo Calera. The effect of a 15-day water-stress period imposed at the beginning of the reproductive phase (WSRP) decreased seed yields 42 and 50% for Bayo Calera and Ojo de Cabra, respectively. In the case of t r e a t m e n t WSVP, in which the duration of the stress was different for the cultivars, the reduction in seed yield was smaller t h a n t h a t of the t r e a t m e n t WSRP, even though the duration of the former t r e a t m e n t was longer. The t r e a t m e n t WSVR was the most affected by the water stress, as expected, since the duration of this particular t r e a t m e n t included the total a m o u n t of time of the two waterstress treatments, WSVP and WSRP. In this case, the full-season cultivar Ojo de Cabra was the most adversely affected due to the longer duration of the treatment. In dry beans a loss of reproductive organs can occur even under the most favorable conditions. This loss can be of different magnitude in the same cultivar depending on the environmental conditions. In the present study, the
88 quantity of reproductive organs shed during the development of the crop under the different water treatments was not determined; however, a major shed of flowers and small pods was observed in the water-stress treatments. Without exception, the yield components were diminished by the stress treatments, and this decrease was more severe for the drought treatments with longer duration (i.e. WSVR). However, considering the duration of each water-stress treatment, the stress imposed at the beginning of the reproductive phase causes a greater decrease on the yield components. In general, the number of pods per plant was the most affected by the treatments studied (Table 3 ). In each treatment, the percentage of normal and abortive seeds and undeveloped ovules was determined in 100 pods per plot. In all treatments, including the control treatment, the percentage of seeds normally developed in the pods ranged from 72 to 78% with Bayo Calera and from 55 to 65% with Ojo de Cabra (data not shown); this suggests strong intraovary competition even under favorable conditions.
Experiment 1982 Crop growth represented by node number per plant, LAI and biomass reached maximum values between 58 and 68 DAB, during flowering (Figs. 3 and 4). For number of nodes per plant, significant differences were found only among cultivars during the first three sampling times; later, significant differences were also found for the effect of the water treatments. The effect of water stress upon this trait was visible at the end of the treatments. A relative recovery was evident for the treatment WSVP, particularly in Bayo Calera. As expected for this trait, the full-season cultivar Ojo de Cabra was highly superior to Bayo Calera and Pinto Nacional 1. The pattern of response of biomass to water treatments was very similar to that of node number per plant for all cultivars, therefore data for biomass are not shown. For LAI, no significant differences were detected for any of the sources of variation during the two first dates sampled. At the 3rd sampling time, the mid and full-season cultivars Bayo Calera and Ojo de Cabra showed significantly higher values than the early cultivar Pinto Nacional. At this time, the effect of the treatment WSVP was also evident. In general, the effect of treatment WSRP upon this trait is notable because it highly increased the rate of senecence. Treatment WSVP showed a recovery after the end of the water shortage. The three cultivars under treatment WSVP flowered and reached physiological maturity 3 days before those in the other treatments. Seed yield was significantly different for the three cultivars. The rank of the cultivars was: Pinto Nacional 1 > Bayo Calera > Ojo de Cabra, with mean yields of 176, 143 and 131 g / m 2 respectively (Table 4). In the case of the water treatments, considering the seed yield of the control as 100%, respective yields of WSVP and WSRP were as follows: 83 and 66%
89
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78
AFTER
DAYS
I
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I
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I 38
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PLANTING
Fig. 3. Number of nodes per plant of three indeterminate dry-bean cultivars,Pinto Nacional I (PN1), Bayo Calera (BC) and Ojo de Cabra (OC), under three water treatments: Control, wellwatered; W S V P , water-stress vegetative phase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration). Verticalbars represent leastsignificantdifference (P < 0.05) for the water treatments; 1982. PN1
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PLANTING
Fig. 4. LAI of three indeterminate dry-bean cultivars,Pinto Nacional I (PN1), Bayo Calera (BC) and Ojo de Cabra (OC), under three water treatments: Control, well watered; W S V P , water-stress vegetative phase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration ).Verticalbars represent leastsignificantdifference (P < 0.05) for the water treatments; 1982.
90 TABLE 4 Seed yield and yield components of three dry-bean cultivars under three water treatments, Durango, Mexico, 1982. Treatment +
Pinto Nacional 1 Control WSVP WSRP
Seed yield (g/m 2)
Pods/plant
Seeds/pod
Seed weight (g/100)
212a* 176b 140c
23.7 18.6 16.3
4.0 3.8 3.8
33.5 33.4 31.0
177a 143b 108c
18.3 12.9 12.3
3.6 3.6 3.3
40.1 10.0 38.8
162a 125b 106c
24.1 15.1 12.8
3.1 2.9 3.0
31.6 31.5 31.8
Bayo Calera Control WSVP WSRP
Ojo de Cabra Control WSVP WSRP
+ Treatment: Control, well-watered; W S V P , water-stressvegetativephase (15 days duration); and W S R P , water-stress reproductive phase (15 days duration). *Tukey's test at P < 0.05, mean values followed by the same letterare not significantlydifferent.
in Pinto Nacional 1, 81 and 61 in Bayo Calera, and 77 and 65% in Ojo de Cabra. Thus, even though both water-stress treatments were of the same duration and intensity, the stress imposed at the beginning of the reproductive phase reduced seed yield twice as much as the reduction observed when the stress was imposed at the vegetative phase. As in 1981, the number of pods per plant was the yield component most affected by the water-stress treatments. DISCUSSION
The mid and full-season cultivars, Bayo Calera and Ojo de Cabra, showed different values than expected for harvest index (HI) under stress in 1981 (Table 5 ). These responses were in part due to the differences in duration ofphenological stages. Aspinall et al. (1964) have emphasized that "the organ which is growing most rapidly at the time of the stress is the one most affected". This relationship can actually lead to an increased HI under water stress because of strong reduction in vegetative growth (Donald and Hamblin, 1976). In 1982, all cultivars showed a decrease in HI under stress when compared to control. The early-season cultivar Pinto Nacional 1 showed a high proportion of shoot dry-matter in seeds, which indicates a higher capacity of remobilization of carbohydrates and other compounds to the developing seeds. Hall and Patel (1985)
91 TABLE 5 Modifiedharvest index* of three indeterminate dry-bean cultivars under four water treatments, Durango, Mexico Treatment +
Control WSVP WSRP WSVR
Cultivar Pinto Nacional
Bayo Calera
Ojo de Cabra
1981
1982
1981
1982
1981
1982
-
0.77 0.75 0.60 -
0.40 0.38 0.46 0.62
0.53 0.49 0.40
0.44 0.69 0.51 0.46
0.51 0.46 0.49 -
*Calculated by dividing the seed yield by the highest value for biomass among the phenological stages sampled for each cultivar and water treatment. +Treatments: Control, well-watered; WSVP, water-stress vegetative phase (different duration depending on cultivar and season); WSRP, water stress reproductivephase (15 days duration); and WSVR, water-stress vegetative and reproductive phases (different duration depending on cultivar). indicated similar findings with cowpea strains selected visually for early production of mature pods. In both years, m a x i m u m values for LAI were found at the end of the stress t r e a t m e n t s in the middle of the flowering period. These results, and the fact t h a t a high positive correlation was found between this trait and seed yield, suggest t h a t the decrease in yield under stress can be related to a decrease in LAI,the latter due to reduction in growth and increased senescense. Even though indeterminate cultivars of this species can compensate for leaf senescence by new growth, it seems t h a t those cultivars showing less senescence during stress are likely to produce better yields. Therefore, as Parsons (1979) indicated, leaf senescence measured on a visual scale could be effective in the process of selection in a breeding program for drought tolerance. All stress treatments evaluated in this study reduced seed yield; however, as indicated elsewhere, the highest reduction was found when the stress was imposed at the beginning of the reproductive phase. This reduction in yield was due mainly to reduction in the number of pods per plant; similar results were found by Robins and Domingo (1956), Dubetz and Mahalle (1969), and Flores-Lui (1982). In this research, a small non-significant reduction in the number of seeds per pod and seed weight was observed. Dubetz and Mahalle (1969) and Flores-Lui (1982) indicated a decrease of these yield components only when the stress was applied late in the season during pod-filling. W i t h respect to the a m o u n t of aborted seeds and undeveloped ovules, the fact t h a t the control t r e a t m e n t showed similar values as those of the stress treatments suggests
92 that strong intra-ovary competition occurred under all evaluated treatments. This may be due to limited source in relation to the strength of the sink during the seed-filling period, or to the fact that, while carbohydrate is available, it is not effectively remobilized. Harvestable yield rather than mere plant survival is the goal in any agricultural situation involving annual seed crops. However, it is well known that cultivars which yield the best in dry years may not be the best-yielding cultivars in moist years (Parsons, 1979). In the particular case of the Mexican plateau, farmers are concerned with yield stability from year to year. In the case of this study, a strong association was found over all treatments between biomass and seed yield; this result throws some light on the fact that farmers in this area use just type-III cultivars when raising beans under rainfall conditions. It is known that this type of bean possesses a certain phenotypic plasticity by having an extended flowering period and the capability to produce new leaves in the face of drought-induced senescence. This plasticity helps them to cope with short drought periods. Moreover, type-III cultivars can produce more biomass than indeterminate type-II's and determinate type-I's (typeIV cultivars, which can produce the highest values in biomass among all types of beans, have a long growing cycle and are unadapted to the Mexican semiarid highland). Thus, it is likely that farmers prefer to grow type-III cultivars because of their morphophenological characteristics. In this study, all growth and yield-related parameters were reduced by water stress. However, the results have some implications for the breeding for droughttolerance. The possible use of visual score for leaf senescence was already mentioned, and since LAI and biomass were highly correlated to yield, it seems that these traits may be used to select for drought-tolerance under stress. A necessary step before deciding which of these traits is the most appropriate is to define their correspondent heritability values. A priori, it seems that the use of a visual score on general vigor and leaf senescense under stress, combined with a high number of pods per plant at maturity, will allow breeder's to identify promising genotypes.
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Donald, C.M. and Hamblin, J.,1976.The biologicalyieldand harvest index of cerealsas agronomic and plant breeding criteria.Adv. Agron., 28: 361-405. Doss, B.D., Pearson, R.W. and Rogers, H.T., 1974. Effects of soilwater stress at various growth stages on soybean yield.Agron. J., 66: 297-299. Dubetz, S. and Mahalle, P.S., 1969. Effect of soilwater stress on bush beans Phaseolus vulgaris L. at three stages of growth. J. Am. Soc. Hortic. Sci.,94: 479-481. Flores-Lui, L.F., 1982. Flowering, pod set,yieldand dry matter partitioningof beans (Phaseolus vulgaris L.) in response to water stress and flower and leafremoval. Ph.D. thesis,University of California,Davis, 116 pp. Hall, A.E. and Patel, P.N., 1985. Breading for resistance to drought and heat. In: S.R. Singh and K.O. Rachie (Editors), Cowpea: Research, Production and Utilization.Wiley, New York, pp. 137-151. Hiler, E.A., van Bavel, C.H., Hossain, M.M. and Jordan, W.R., 1972. Sensitivity of southern peas to plant water deficit at three growth stages. Agron. J., 64: 60-64. Hsiao, T.C., 1973. Plant responses to water stress. Annu. Rev. Plant Physiol., 24: 519-570. Parsons, L.R., 1979. Breeding for drought resistance: what plant characteristics impart resistance? Hortic. Sci., 14: 590-593. Robins, J.S. and Domingo, C.E., 1956. Moisture deficit in relation to the growth and development of dry beans. Agron. J., 48: 67-70. Salter, P.J., 1963. The effect of wet or dry soil conditions at different growth stages on the components of yield of a pea crop. J. Hortic. Sci., 38: 321-334. Sionit, N. and Kramer, P.J., 1977. Effect of water stress during different stages of growth of soybeans. Agron. J., 69: 274-278. Stansell, J.R. and Smittle, D.A., 1980. Effects of irrigation regimes on yield and water use to snap beans (Phaseolus vulgaris L.) J. Am. Soc. Hortic. Sci., 105: 869-873. Stoker, R., 1974. Effect on dwarf beans of water stress at different phases of growth. N.Z.J. Exp. Agric., 2: 13-15. Turk, J.J., Hall, A.E. and Asbell, C.W., 1980. Drought adaption of cowpea. I. Influence of drought on seed yield. Agron. J., 72: 414-420.