PHysIoLoGICAL PerForMANCe, yIeLd, ANd QUALITy oF dry BeAN seeds UNder droUGHT sTress

Interciencia ISSN: 0378-1844 interciencia@ivic.ve Asociación Interciencia Venezuela Castañeda-Saucedo, Ma. Claudia; Córdova-Téllez, Leobigildo; González-Hernández, Víctor A.; Delgado-Alvarado, Adriana; Santacruz-Varela, Amalio; García-de los Santos, Gabino PHYSIOLOGICAL PERFORMANCE, YIELD, AND QUALITY OF DRY BEAN SEEDS UNDER DROUGHT STRESS Interciencia, vol. 34, núm. 10, octubre, 2009, pp. 748-754 Asociación Interciencia Caracas, Venezuela Available in: http://www.redalyc.org/articulo.oa?id=33913147012 How to cite Complete issue More information about this article Journal's homepage in redalyc.org Scientific Information System Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Non-profit academic project, developed under the open access initiative PHYSIOLOGICAL PERFORMANCE, YIELD, AND QUALITY OF DRY BEAN SEEDS UNDER DROUGHT STRESS Ma. Claudia Castañeda-Saucedo, Leobigildo Córdova-Téllez, Víctor A. González-Hernández, Adriana Delgado-Alvarado, Amalio Santacruz-Varela and Gabino García-de los Santos SUMMARY Net photosynthesis (A), respiration (RE), stomatal conductance (gs), transpiration rate (E), yield, and its components, as well as physical and physiological quality of seeds were evaluated on dry bean (Phaseolus vulgaris L.) plants cv. ‘Otomí’, subjected to drought stress during the stages of flowering (F), pod formation (PF) and seed filling (SF). After 3 days under drought stress, gs, E and A decreased by more than 50% at F, PF and SF, respectively; after 10 days of stress, there was total inhibition of those processes, whereas the maximum reductions showed by RE were 42, 62, and 85% in F, PF and SF, respectively. Drought stress induced seed yield reductions of 10, 57, and 50% at F, PF and SF, respectively. High yield losses at PF and SF were caused by reductions in the number of seeds and pods per plant and seeds per pod. At the SF stage the loss in yield was moderate, because at this stage the plants were able to form new leaves and delay pod formation until water stress was over. The physiological quality was not affected by drought stress, even though the weight of 1000 seeds was reduced by about 10%. Introduction applied. Nielsen and Nelson (1998) also reported reductions of 695 and 940kg·ha-1 in black bean plants subjected to drought stress during the flowering and grain filling stages, respectively, in relation to the control plants under irrigation. Similarly, Acosta and Kohashi (1989) found 42 and 50% yield reductions in ‘Bayo Calera’ and ‘Ojo de Cabra’ varieties when the drought stress was imposed from the end of the vegetative stage through physiological maturity. Nuñez et al. (2005) registered 60% of yield reduction in dry bean, which was attributed to losses of 63.3% in pods per plant, 28.9% in seeds per pod, and 22.3% in seed weight. Water is the main limiting factor for dry bean (Phaseolus vulgaris L.) production under rainfed conditions in Mexico, causing significant yield reduc- In legumes, the reproductive stage is the most sensitive stage to drought stress (Nielsen and Nelson, 1998), whether it takes place during flower formation (Pedroza and Muñoz, 1993), full flowering (Pimentel et al., 1999), pod formation (Castañeda et al., 2006), or grain filling (Nielsen and Nelson, 1998). This is because the water deficit causes falling or abortion of reproductive structures (Acosta and Kohashi, 1989), as it occurs with the pistil in soybean (Glycine max L.; Kokubun et al., 2001) and pollen in dry bean (Shen and Webster, 1986), which results in a low number of pods per plant (Dornbos et al., 1989; Boutra and Sanders, 2001) and seeds per pod (Nielsen and Nelson, 1998). As a consequence of a low seed production during drought stress the average yield is reduced (Acosta and Kohashi 1989; Acosta et al., 2004; Núñez et al., 2005). In many legume species experimenting water deficit during the flowering and grain filling stages the average yield may show reductions of 40-60% compared with irrigated plants (Acosta and Kohaski, 1989; Nilsen and Nelson, 1998). Yield reduction may be a result of losses in pods per plant, low number of seed per pod and low seed weight (Núñez et al., 2005). Acosta et al. (2004) found an average yield reduction of 53% in eight varieties of dry bean of different origin and growth habit under drought stress, compared with the negative control in which five irrigations levels were tions (Pérez et al., 1999). Under drought stress conditions, dry bean presents morphological plasticity characterized by overproduction of reproductive structures (Acosta et al., 2003) and by physiological changes, such as reduction of stomatal conductance (Pattanagul and Madore, 1999). This in turn causes a decrease in transpiration (Vieira et al., 1992) and photosynthesis (Pattanagul and Madore, 1999) and losses of sugars utilized to support growth and development (Pattanagul and Madore, 1999). In México, over 1×10 6ha are planted with dry bean, mainly at the highland northern plains 1800-2200masl, with annual mean precipitation of 200-400mm (Schneider et al., 1997). In this region, farmers utilize seed from the previous cycle, whose physiological quality is unknown. In dry Keywords / Electrical Conductivity / Germination / Phaseolus vulgaris / Photosynthesis / Respiration / Stomatal Conductance / Received: 07/06/2009. Modified: 10/09/2009. Accepted: 10/12/2009. María Claudia CastañedaSaucedo. Agronomist, Universidad Autónoma de Chapingo (UACH), Mexico. M.Sc. and Ph.D., Colegio de Postgraduados (COLPOS), Mexico. Professor, Universidad de Guadalajara (UDG), Mexico. Address: CUSUR-UDG. Av. Colón S/N Km1 carretera Guadalajara-Cd. Guzmán. Cd. Guzmán, Jal. 748 México. C.P. 49,000. e-mail: csaucedo@colpos.mx Leobig ildo Córdova-Téllez. Agronomist, UACH, Mexico. M.Sc., Mississippi State University, USA. Ph.D., Iowa State University (IASTATE), USA. Professor, COLPOS, Mexico. Víctor A. González-Hernández. Agronomist, UACH, Mexico. M.Sc., COLPOS, Mexico. Ph.D., University of NebraskaLincoln, USA. Professor, COLPOS, Mexico. Adriana Delgado-Alvarado. Agricultural Chemist, Universidad Veracruzana, Mexico. M.Sc., COLPOS, Mexico. Ph.D. University of Sheffield, UK. Professor, COLPOS, Puebla, Mexico. Amalio Santacruz-Varela. Agronomist, UACH, Mexico. M.Sc., 0378-1844/09/10/748-07 $ 3.00/0 COLPOS, Mexico. Ph.D., IASTATE, USA. Professor, COLPOS, Mexico. Gabino García-de los Santos. Agronomist, UACH, Mexico. M.Sc., COLPOS, Mexico. Ph.D. Oregon State University, USA. Professor, COLPOS, Mexico. OCT 2009, VOL. 34 Nº 10 COMPORTAMIENTO FISIOLÓGICO, RENDIMIENTO Y CALIDAD DE SEMILLA DE FRIJOL SOMETIDO A SEQUÍA Ma. Claudia Castañeda-Saucedo, Leobigildo Córdova-Téllez, Víctor A. González-Hernández, Adriana Delgado-Alvarado, Amalio Santacruz-Varela y Gabino García-de los Santos RESUMEN Se evalúo la fotosíntesis neta (A), respiración (RE), conductancia estomática (gs), tasa de transpiración (E), rendimiento y sus componentes, así como la calidad física y fisiológica de semillas de plantas de frijol (Phaseolus vulgaris L.) cv. ‘Otomí’ sometidas a sequía durante las etapas de floración (F), formación de vaina (FV) y llenado de semilla (LLS). Después de 3 días de sequia, gs, E y A disminuyeron en más de 50% en F, FV y LLS, respectivamente; después de 10 días de estrés hubo inhibición total de estos procesos, mientras que las reducciones máximas mostradas por RE fueron de 42, 62 y 85% en F, FV y LLS, respectivamente. La sequía propició reducciones en el rendimiento de semilla de 10, 57 y 50% en F, FV y LLS, respectivamente. Las altas pérdidas de rendimiento en FV y LLS se debieron a las reducciones en número de semillas, de vainas por planta y de semillas por vaina. En F la disminución en rendimiento fue moderada, debido a que en esta etapa las plantas formaron nuevas hojas y retardaron la formación de vainas cuando terminó la sequía. La calidad fisiológica de las semillas no resultó afectada por la sequía, aun cuando el peso de 1000 semillas tuvo una reducción de casi 10%. COMPORTAMENTO FISIOLÓGICO, RENDIMENTO E QUALIDADE DA SEMENTE DO FEIJÃO SUBMETIDO À SECA Ma. Claudia Castañeda-Saucedo, Leobigildo Córdova-Téllez, Víctor A. González-Hernández, Adriana Delgado-Alvarado, Amalio Santacruz-Varela e Gabino García-de los Santos RESUMO Avaliou-se a fotossíntese neta (A), respiração (RE), condutância estomática (gs), taxa de transpiração (E), rendimento e seus componentes, assim como a qualidade física e fisiológica de sementes de plantas de feijão (Phaseolus vulgaris L.) cv. ‘Otomí’ submetidas à seca durante as etapas de floração (F), formação de vagens (FV) e enchimento da semente (LLS). Depois de 3 dias de seca, gs, E e A diminuiram em mais de 50% em F, FV e LLS, respectivamente; depois de 10 dias de estresse houve inibição total destes processos, enquanto que as reduções máximas mostradas por RE foram de 42, 62 e 85% em F, FV e bean, a stress of 30 days imposed after flowering caused reductions of 24 and 19% in the weight and volume of 100 seeds (Pérez et al., 1999), and Heatherly (1993) reported germination of soybean below 80% after a drought stress imposed during the reproductive stage. In contrast, Vieira et al. (1992) did not detect effects of a similar drought on seed ger m ination and vigor, even though t he nu mb er of i m m at u re, wrinkled, and opaque-coat seed was high. In the present study the physiological responses of d r y bea n on plant, yield and its components, and on the physical and physiological quality of the seed harvested are evaluated in plants subjected to drought stress during the stages of flowering, pod formation and seed filling. Materials and Methods The study was carried out under greenhouse conditions at Montecillo, State of México (19º29’N, 98º54’W, and 2250masl), using the dry bean (Phaseolus vulgaris L. cv. ‘Otomí’) of determinate growth habit, which is recommended for the semiarid highland plains of México (Schneider et al., 1997). Seeds were planted into 6 l plastic containers, using a mixture of loam soil, river sand, peat moss and agrolite (2:2:1:1) as substrate. The field capacity (FC) and the permanent wilting point (PWP) of the substrate were determined through the pressure pot and the pressure membrane, and a moisture retention curve was generated. Drought stress treatments were applied as follows: 1) at OCT 2009, VOL. 34 Nº 10 LLS, respectivamente. A seca propiciou reduções no rendimento da semente de 10, 57 e 50% em F, FV e LLS, respectivamente. As altas perdas de rendimento em FV e LLS foram devido às reduções em número de sementes, de vagens por planta e de sementes por vagem. Em F a diminuição no rendimento foi moderada, devido a que nesta etapa as plantas formaram novas folhas e retardaram a formação de vagens quando terminou a seca. A qualidade fisiológica das sementes não resultou afetada pela seca, mesmo quando o peso de 1000 sementes teve uma redução de quase 10%. the R6 stage, during flowering (F); 2) at the R7 stage, pod formation (PF); 3) at R8, seed filling (SF), and 4) control, under irrigation (I). For the stress treatments, water supply was suspended until reaching the PWP + 10 days, which is equivalent to 11.5% of the moisture content of the substrate. At the end of the stress, periodic irrigation was resumed. The control was maintained at field capacity (22.5% moisture). Leaf and pod water potentials (Ψl and Ψp) were determined at each stage using a Scholander pump model A699 (Soil Moisture Equipment Corp., Santa Barbara, CA, USA). Treatments were distributed under a randomized complete blocks design with three replications, where the experimental unit was a group of 20 pots with a single plant per pot. Each pot was daily weighed during plant development and the amount of consumed water was estimated through the difference of weights from consecutive days. Then, based on the moisture retention curve, the required amount of water was supplied through irrigation for maintaining the substrate at field capacity (22.5%), except during the stress periods. The mean values of temperature and relative humidity inside the greenhouse during the growth season ranged 17-23°C and 57-75%, respectively. Physiological traits Net photosynthesis rate (μmol CO 2 ·m -2 ·s -1), stomatal conductance (mmol H 2 O ·m ‑2 ·s -1) and transpiration rate (mmol H 2O·m -2 ·s -1) were measured between 11:00 749 and 13:00 under illuminated conditions with a portable apparatus LI-6400 (LICOR Inc., Lincoln, NE, USA). Foliar respiration (μmol CO2·m-2·s-1) was also measured with the same instrument after covering the assimilation chamber with a plastic card until total darkness, then allowing a 100s period to reach equilibrium. The five readings were collected from a leaf of the upper stratum and another one from the lower stratum of the plant, in each block, at -2 days (prior to stress) and at 3, 5 and 10 days during stress, plus an additional measurement 8 days after the recovery irrigation. During the measurements across all above mentioned dates, the photosynthetic active radiation varied from 1125 to 1500μmol·m2 -1 ·s , the vapor pressure deficit ranged 2-5kPa, and the air temperature from 19 to 23oC. of the test, considering only normal seedlings; 2) Electrical conductivity test (EC), used as an indicator of membrane damages, performed according to the ISTA protocols (ISTA, 2005) recommended for pea, in four replications of 50 seeds, after being weighed and placed into 250ml of deionized water at 21ºC for 24h; the readings were then taken with an Oakton meter WD-35607-00 (Singapore) and the electrical conductance (Μs·cm-1) was calculated using the equation EC= reading of the target/weight of the seed (g)= Μs·cm-1·g-1; 3) Accelerated aging test, another seed vigor test, was performed according to the protocol of the ISTA (2005) recommended for soybean, in four replications of 25 seeds placed on a screen inside a plastic box that contained 40ml of de-ionized water, and then incubated at 41ºC for 72h; afterwards, an standard germination test was performed, and at the end of the test the average weight per seedling (mg) was obtained after they were dried at 70ºC for 76h. The data from each date were analyzed with the SAS (Statistical Analysis System) program version 6.12, through analysis of variance of randomized complete blocks design, and treatments compared by a multiple means compari- son test (Tukey, p< 0.05). It should be noted, however, that the data were not submitted to homogeneity or normality tests. Results and Discussion bean in this study was somewhere between moderate and severe. No reports on Ψpod were found. Stomatal conductance The drought imposed at the three stages of crop development drastically decreased leaf stomatal conductance (gs) At the end of the stress in both upper and lower strata treatments, leaf water poof the plant. In the upper stratential (Ψl) values were -1.1, -1.1, -1.2 and -0.6MPa for F, tum, gs decreased after 3 days PF, SF and I, respectively; under stress to 350 (75%), 291 and in pods (Ψpod) they were (87%) and 466 (92%) mmol -1.2, -1.5 and -0.7MPa for PF, H 2O·m-2 ·s-1 in F, PF and SF, respectively (Figure 1a, b and SF and I, respectively. Such c). Then, from the 5 th day results indicate that drought through the end of the stress caused large reductions of the period, gs reached zero in the Ψ in both organs, in relation stress treatments. In the lower to the control under irrigastratum, after 3 days under tion, but pods maintained a stress the gs had already delower Ψ than leaves in all creased 79, 99 and 100%, in treatments, possibly to favor F, PF and SF, respectively, sap f low towards the pods. while in the rest of the stress Acosta and Kohashi (1989) period gs was zero (Figure 1d, also reported values of Ψl of -1.5MPa in dry bean leaf sube and f), implying a more senYield and its components jected to drought stress for 15 sitive stomatal closing than in days at the onset of flowering. upper leaves. At the 10 th day, The harvest of pods was plants of the SF treatment had In chickpea (Cicer arietinum carried out at two periods, already lost their lower leaves, L.) pods, Ma et al. (2001) on November 24 th for treatpossibly because the leaves registered a Ψl of -1.4MPa ments I, PF and SF, and one after applying drought stress were older, and therefore more month later for treatment F, during 10 days. In maize (Zea sensitive to stress, presenting due to the fact that plants demays L), Schussler and Westan early senescence (Brevedan layed flowering as a result of gate (1991) consider that a and Egli, 2003). stress. The harvested pods moderate drought stress durMiyashita et al. (2005) also were dried at room temperaing flowering corresponds to registered a rapid decrease of ture; then seed yield per plant a leaf Ψl of -0.7MPa, and a gs in kidney bean after 2 days severe one to -1.1MPa. There(g), number of pods per plant, of stress, with values close to fore, the stress applied to dry seeds per plant, seeds per pod zero at the 5th day, and zero at the 7th day of drought stress. and weight of pod (g) were Stomatal closing can determined. also occur with a high leaf water potential Physical and physiologdue to signals from ical quality of the seed the root, as has been proposed by Miyashita The physical quality et al. (2005). was quantified through The lower recovery the weight of 1000 rate of gs observed in seeds (WTS), accordthe upper stratum in F ing to Moreno (1984), is attributed to the fact except that four replicathat the plants under tions of 100 seeds were this treatment began used per treatment. The forming new leaves physiological quality was and new f lowers, determined through: 1) so that the previous Standard germination leaves possibly became test (ISTA, 2005), in suppliers of water and four replications of 25 nutrients for the newly seeds, using sand as substrate, and measured Figure 1. Stomatal conductance of upper leaf (UL; a, b, c) and lower leaf (LL; d, e,f) of plants constituted tissues; on in a single count carried with drought stress at flowering (F), pod formation (PF), seed filling (SF), and irrigation (I). SI: the other hand, in the lower stratum of plants out 9 days after the start suspension of irrigation, I: irrigation, 8DAI: 8 days after irrigation. 750 Water potential (Ψ) OCT 2009, VOL. 34 Nº 10 in F, gs had completely recovered. As previously indicated, in PF and SF the lower leaves had already fallen down, probably because they were more mature than in F, implying that younger leaves are more resistant to drought, having greater capacity of osmotic adjustment, as pointed out by Turner and Jones (1980). assimilation rates, as well as those of transpiration, are strongly related with stomatal closure, as also indicated by Cruz de Carvalho et al. (1998). After 8 days from the recovery irrigation, gs, E and A of the upper leaves had completely recovered in PF and SF treatments, whereas at F they had only recovered by 58, Transpiration rate 55 and 51%, respectively (Figures 1a, 2a, Parallel to gs, tranand 3a). The large sispiration (E) decreased Figure 2. Transpiration rate of upper leaf (UL; a, b, c) and lower leaf (LL; d, e, f) of plants militude of responses drought stress at flowering (F), pod formation (PF), seed filling (SF), and irrigation (I). SI: as a result of drought in with among gs, E and A suspension of irrigation, I: irrigation, 8DAI: 8 days after irrigation. both strata of the plant. is due to the fact that In the upper stratum, both E and A are gas 100% at F, PF and SF, respecand SF, respectively (Figure after 3 days under drought exchange processes occurring tively, and after the fifth day 3a, b, c), and after the 5th day stress the transpiration rate through the stomata pores, photosynthesis was completely the inhibition was complete decreased to 6.8 (73%), 4.4 so that the smaller the valinhibited in all the treatments, in all the treatments (Figure (66%) and 7.6 (83%) mmol ue of gs the smaller would except for PF, where the in3d, e, f). Reductions in photoH 2O·m -2 ·s -1 at F, PF and SF, be E and A, and vice versa hibition was 89% at the 5 th synthesis coincide with those respectively (Figure 2a, b, (Hsiao, 1973). The recovery day. Miyashita et al. (2005) reported by several authors c). From the 5th day through levels achieved in F are simialso reported a rapid decrease such as Dornbos et al. (1989) the end of the stress, E belar to those registered in kidin the photosynthetic rate of and Brevedan and Egli (2003) came zero in all the stress ney bean by Miyashita et al. kidney bean, just after 2 days in soybean, Castañeda et al. treatments. Similar effects of (2005), who reported that the of drought stress. According (2006) in dry bean subjected drought stress were reported recovery of the physiological to Brevedan and Egli (2003), to drought stress during seed by Miyashita et al. (2005) for processes of bean improves as drought stress during seed fillfilling, Pattanagul and Makidney bean, with transpiradrought stress is lowered; with ing causes a rapid reduction dore (1999) in Coleus blumei tion rates of zero at the 7th a stress of -0.6MPa the recovof the assimilation rate of carsubjected to drought stress day of stress, and by Dornbos ery is 100% with a stress of -2 -1 bon, registering 0μmol·m ·s in 2-month old plants, and et al., (1989) for soybean. -1.2MPa recovery is 80, 60 within 15 days. by Schussler and Westgate Damages were more severe and 40% for the photosynPhotosynthetic activity in (1991) in maize (Zea mays in the lower stratum, in such thetic rate, transpiration rate the lower stratum decreased L.) under moderate (-0.7MPa) a magnitude that after the 3rd and stomatal conductance, more rapidly than in the upand severe (-1.1MPa) drought day of stress leaf transpiration respectively; with a stress of per one. By the third day it stress during flowering. Such rate decreased by 71, 99 and -1.9MPa recovery is only 50, had decreased 61, 100 and reductions in photosynthetic 100% at F, PF and SF, respec35 and 15%. In the lower stratively; and from the 5th tum, the gs, TR and NP day on it reached zero completely recovered in for all the treatments; F, the only treatment in remarkably, plants which plants retained stressed at SF had lost lower leaves after the their leaves at the 10th drought. This is attribday under stress (Figuted to the ability of ure 2d, e, f). these leaves to rehydrate and to prevent damages Net photosynthesis of the chloroplasts. The photosynthesis rate (A) under drought and post-drought recovery varied in a very similar manner as conductance and transpiration. After 3 days of stress, net photosynthesis of the upper stra- Figure 3. Net photosynthesis of upper leaf (UL; a, b, c) and lower leaf (LL; d, e, f) of plants tum decreased by 67, with drought stress at flowering (F), pod formation (PF), seed filling (SF), and irrigation (I). SI: 57 and 75% at F, PF suspension of irrigation, I: irrigation, 8DAI: 8 days after irrigation. OCT 2009, VOL. 34 Nº 10 Respiration Contrary to the previous processes, foliar respiration experienced small changes due to drought stress, probably because respiration is a physiological process indispensable to maintain the cells alive as it 751 provides the chemical of the vegetative stage energy for metabolic through physiological processes, particularly maturity was located in under low or null phothe branches of lower tosynthesis. In the upnodes, where abortion per stratum, significant occurred over 100% of effects did not appear pods, while in the upuntil 5 days of stress, per nodes (nodes 5 to decreasing by 55 and 10) only 15% of abor36% at F and SF, retion occurred. spectively; after 10 It should be ta ken days reductions were of into account that the 42, 62 and 85% at F, water deficit imposed PF and SF, respectively at F caused flowering (Figure 4a, b, c). It is delaying by one month, thus confirmed that the suggesting a mechanism respiratory process is of ontogenetic resistance more resilient to stress to drought, as pointed than photosynthesis, Figure 4. Respiration of upper leaf (UL; a, b, c) and lower leaf (LL; d, e, f) of plants with out by Pedroza and drought stress at flowering (F), pod formation (PF), seed filling (SF), and irrigation (I). SI: sustranspiration, and sto- pension of irrigation, I: irrigation, 8DAI: 8 days after irrigation. Muñoz (1993). Boutra matal conductance and Sanders (2001) also (Hsiao, 1973). In the reported that drought lower stratum, drought stress during flowering retards Table I stress did not cause sigthe development of ovules in Seed yield and its components in dry bean nificant reductions in the bean and detains growth. subjected to drought stress at flowering, first 5 days, except for It was observed that reducpod formation, seed filling, and irrigation F, where respiration detion in seed yield is closely creased 32%; after 10 Treatment Yield (g/ associated to the inhibition of NPPP NSPP WPP (g) NSPP days reductions were of net photosynthesis and, conplant) 77 and 41% at F and sequently, to the production I 12.2 a 8.8 b 35.0 a 1.4 a 3.97 a PF, respectively, and at F of photoassimilates in the 11.0 b 11.1 a 36.4 a 0.97 b 3.27 b SF there were no leaves. PF treatments with no formation 5.2 c 5.3 c 16.2 b 1.0 b 3.07 b Castañeda et al. (2006) SF of new leaves (i.e. PF and 6.1 c 5.9 c 19.2 b 1.0 b 3.30 b also found small changes SF). Such an inhibition might 1.1138 1.4312 5.073 0.1824 0.2942 in respiration due to the LSD 0.05 have reduced the supply of effect of drought stress NPPP: number of pods per plant, NSPP: number of seeds per plant, WPP: weight of nutrients toward reproducduring seed filling in pod, NSPP: number of seeds per pod, I: irrigation, F: flowering, PF: pod formation, tive organs, as pointed out by dry bean cv. “Negro SF: seed filling, LSD 0.05: least significant difference at α=0.05. Means with the same Raper and Kramer (1987). Precoz”. At the 8th day letter in the columns are not significantly different (Tukey, p<0.05). The results allow to infer after the recovery irrigathat the highest tolerance to tion, respiration of both upper drought of dry bean is onnumber of pods per plant as ering caused yield increases and lower strata completely togenic, because the severe the principal cause of yield of 30-70% in relation to the recovered in all the treatments drought stress imposed at losses of bean subjected to control without stress. with remaining leaves (Figure flowering causes much less drought stress, followed by At PF, the loss in yield 4d, e, f). damage in yield than that at the number of seeds per pod was caused by the reduction later stages, as the plant has and seed weight. of 54, 40 and 23% in the Yield and yield components the opportunity to continue The low decrease (10%) in number of seeds per plant, developing after the drought, yield at F, despite of 31 and pods per plant and seeds per Drought stress caused losseven though the effects of the 18% reductions in weight of pod, respectively. At SF, the es in yield of 1.2g (10 %), drought on A, E, and gs are pod and number of seeds per loss in yield was a result of 7.0g (57%) and 6.1g (50%) equally severe in all three pod, was due to partial coma reduction of 45% in the per plant at F, PF and SF, studied phenological stages. pensation through increases number of seeds per plant, respectively, wit h respect of 26 and 4% in the number as a consequence of a reducto the control under irrigaSeed quality of pods and seeds per plant tion of 33% in the number tion (Table I). It is thus in(Table I), implying that durof pods per plant and 19% ferred that the ‘Otomí’ bean Regarding physical qualing flowering the bean plant in seeds per pod (Table I). is much more sensitive to ity, drought caused reducstill has the opportunity to The effect of drought stress drought stress during PF and tions of 14, 8 and 10% in the modify its structure when it on the weight of pod was SF than during F. Castañeda weight of 1000 seeds during sets the new flowers and pods essentially the same in all et al. (2006) also reported F, PF and SF, with respect to generated in post-drought in the th ree developmental higher sensitivity of another the control (Table II). França the upper part of the plant, stages, as reductions were dry bean variety to drought Neto et al. (1993) in soybean provided that only the lower 31, 29 and 29% at F, PF and stress at the pod formation and Pérez et al. (1999) in leaves are affected. Núñez SF, respectively. Acosta and stage. Deproost et al. (2004) dr y bean repor ted a sim iet al. (2005) also observed Kohashi (1989), Nielsen and obser ved t hat a moderate lar effect of drought stress that the most severe effect Nelson (1998) and Nuñez et stress imposed during flowapplied during seed filling. of the drought from the end al. (2005) also identified the 752 OCT 2009, VOL. 34 Nº 10 The physiological quality of the seed, measured as percentage of normal seedlings obtained through the standa rd ger m ination test and accelerated aging test, was not significantly affected by drought stress (Table II). Seed vigor measured through the dry weight of the seedling was reduced by 12 and 18% after imposing the accelerated aging test, but only in plants to which drought had been imposed at PF and SF. This result shows again that F in bean is the developmental stage most tolerant to drought. Similar effects of drought on seed physiological quality have been reported by Castañeda et al. (2006) in bean, Fougereux et al. (1997) in pea, Ghassemi-Golezani et al. (1997) in maize and sorghum, and Zalewsk i et al. (2001) in lupin (Lupinus angustifolius L.) and triticale (Triticum × Secale). Electrical conductivity of the seeds showed no significant effects from drought stress imposed during F, PF and SF (Table II), thus indicating that these treatments did not affect the membrane permeability of the seeds. In seeds of maize and sorghum (Sorghum bicolor L. Moench) harvested from plants previously subjected to drought stress, there were also no significant effects in electrical conductance (Ghassemi-Golezani et al., 1997). These results suggest that the drought treatments did not cause significant damages in cell membranes of the bean seed. In contrast, in soybean Dornbos et al . (1989) repor ted increases of 19% in electrical conductance of seeds from plants subjected to drought stress during seed filling. Given that the physiological quality of seeds was not affected by drought stress, even though their size was reduced, it is possible to infer that drought caused losses in reserves rather than cellular damage in the embryonic axis. In contrast, Dornbos et al. (1989) found reductions of 12% in germination and Table II Physical and physiological quality in dry bean seeds from plants subjected to three treatments of moisture stress: irrigation, stress at flowering, stress at pod formation and stress at seed filling. Treatment I SF SPF SSF LSD 0.05 WTS (g) PG (%) 349.7 a 302.0 b 321.0 ab 315.0 ab 3.9269 100 a 100 a 100 a 95 a 5.5553 PGAAT DWS-AAT EC (%) (mg) (µs·cm-1g-1) 93 a 90 a 95 a 89 a 18.92 174 a 176 a 153 b 143 b 30.649 29.0 a 28.7 a 28.5 a 28.3 a 1.2383 WTS: weight of 1000 seeds, PG: percentage of germination on the standard test, PGAAT: percentage of germination on the accelerated aging test, DWSAAT: dry weight of seedlings from the accelerated aging test, EC: electrical conductivity, I: irrigation, SF: stress at flowering, SPF: stress at pod formation, SSF: stress at seed filling, LSD 0.05: least significant difference at α=0.05. Means with the same letter in the columns are not significantly different (Tukey, p<0.05). of 5% in the vigor of seed harvested from soybean plants subjected to severe drought stress in the stage of reserve accumulation; and Lin and Markhart (1996) also detected reductions of 11% in the germination of seeds of two species of bean (P. vulgaris and P. acutifolius) grown under conditions of drought and high temperature stresses. Conclusions The drought stress applied to dry bean plants of the ‘Otomí’ variety reduces water potential of leaves and pods by almost half in both upper and lower strata of the plant and at the three studied phenological stages. The reduction of foliar Ψl completely inhibits stomatal conductance and, consequently, transpiration and photosynthesis. Respiration is more tolerant to stress than the other physiological processes evaluated. Drought reduced seed yield, with 5-6 fold losses when it occurred at PF and SF than at F, so that the F stage is more tolerant to drought stress than the PF and SF stages. Reductions in yield are caused by reductions in number of pods and number of seeds per plant, weight and number of seeds per pod, and weight of seeds, except for F, where a 26% increment in the number of pods per plant was observed. Reductions in yield OCT 2009, VOL. 34 Nº 10 are closely associated to photosynthetic inhibition, except for F. Ontogenetic tolerance to drought in bean presented at flowering is attributed to the fact that leaves were younger and that flowering was delayed by a month and resumed when there was no drought. The drought stress applied decreased the amount of accumulated reserves between 8 and 12% in the seed, without affecting either the germinative capacity of the embryo or the integrity of its cellular membranes. ACKNOWLEDGEMENTS The authors thank Efraín Acosta Díaz, Experimental Station of Calera, Zacatecas, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP) for the donation of the bean seeds cv. ‘Otomí’. REFERENCES Acosta DE, Acosta GJA, Padilla RJS (2004) Relación raíz-vástago en frijol bajo dos condiciones de humedad. Agric. Técn. Méx. 30: 63-73. Acosta DE, Amador RMD, Acosta GJA (2003) Abscisión de estructuras reproductoras en frijol común bajo condiciones de secano. Agric. Técn. Méx. 29: 155-168. Acosta GJA, Kohashi SJ (1989) Effect of water stress on growth and yield of indeterminate dry-bean (Phaseolus vulgaris) cultivars. Field Crops Res. 20: 81-93. Boutra T, Sanders FE (2001) Influence of water stress on grain yield and vegetative growth of two cultivars of bean (Phaseolus vulgaris L.). J. Agron. Crop Sci. 187: 251-257. Brevedan RE, Egli DB (2003) Short periods of water stress during seed filling, leaf senescence, and yield of soybean. Crop Science. 43, 2083-2088. Castañeda SMC, Cordova TL, González HVA, Delgado AA, Santacruz VA, García de los SG (2006) Respuestas fisiológicas, rendimiento y calidad de semilla en frijol sometido a estrés hídrico. Interciencia 31: 461-466. Cruz de Carvalho M, Laffray D and Louguet P (1998) Comparison of the physiological responses of Phaseolus vulgaris and Vigna unguiculata cultivars when submitted to drought conditions. Env. Exp. Bot. 40: 197-207. Deproost P, Elsen F, Geypens M (2004) High yields of mechanically harvested snap beans as induced by moderate water stress during flowering. Acta Hort. 664: 205-212. Dornbos DL, Mullen RE, Shibles RM (1989) Drought stress effects during seed fill on soybean seed germination and vigor. Crop Sci. 29: 476-480. Fougereux JA, Doré T, Ladonne F, Fleury A (1997) Water stress during reproductive stages affects seed quality and yield of pea (Pisum sativum L.). Crop Sci. 37: 1247-1252. França Neto JB, K rzyzanowski FC, Henning AA, West SH, Miranda LC (1993) Soybean seed quality as affected by shriveling due to heat and drought stresses during seed filling. Seed Sci. Technol. 21: 107-116. Ghassemi-Golezani K, Soltani A, Atashi S (1997) The effect of water limitation in the field on seed quality of maize and sorghum. Seed Sci. Technol. 25: 321-323. Heatherly LG (1993) Drought stress and irrigation effects on germination of harvested soybean seed. Crop Sci. 33: 777-781. Hsiao TC (1973). Plant responses to water stress. Annu. Rev. Plant Physiol. 24: 519-570. ISTA (2005) International Rules for Seed Testing. International Seed Testing Association. Bassersdorf, Switzerland. 243 pp. Kokubun M, Shimada S, Takahashi M (2001) Flower abortion caused by preanthesis water deficit is not attributed to 753 impairment of pollen soybean. Crop Sci. 41: 1517-1521. Lin TY, Mark hart AH (1996) Phaseolus acutifolius A. Gray is more heat tolerant than P. vulgaris L. in the absence of water stress. Crop Sci. 36: 110114. Ma Q, Behboudian MH, Turner NC, Palta JA (2001) Gas exchange by pods and subtending leaves and internal recycling of CO 2 by pods of chickpea (Cicer arietinum L) subjected to water deficits. J. Exp. Bot. 52: 123-131. Miyashita K, Tanakamaru S, Maitani T, Kimura K (2005) Recovery responses of photosynthesis, transpiration, and stomatal conductance in kidney bean following drought stress. Env. Exp. Bot. 53: 205-214. Moreno ME (1984) Análisis Físico y Biológico de Semillas Agrícolas. Universidad Na- 754 cional Autónoma de México. 382 pp. Nielsen DC, Nelson NO (1998) Black bean sensitivity to water stress at various growth stages. Crop Sci. 38: 422-427. Núñez BA, Hoogenboom G, Nesmith DS (2005) Drought stress and distribution of vegetative and reproductive traits of a bean cultivar. Sci. Agric. 62: 18-22. Pattanagul W, Madore MA (1999) Water deficit effects on raffinose family oligosaccharide metabolism in Coleus. Plant Physiol. 121: 987-993. Pedroza FJA, Muñoz OA(1993) Resistencia ontogénica y filogenética a sequía en Phaseolus vulgaris L. I. Caracteres vegetativos. Agrociencia. Ser. Fitociencia 4: 19-33. Pérez HP, Acosta DE, Padilla RS, Acosta GJ (1999) Effect of drought on seed quality of common bean (Phaseolus vulgaris L.). Agric. Técn. Méx. 25: 107-114. Pimentel C, Hebert G, Silva JVda (1999) Effects of drought on O2 evolution and stomatal conductance of beans at the pollination stage. Env. Exp. Bot. 42: 155-162. Raper CD, Kramer PJ (1987) Stress physiology. In Wilcox JR (Ed.) Soybeans: Improvement, Production , and Uses. 2 nd ed. ASA/CSSA/SSSA, Madison, WI, USA. pp. 589-641. Schneider KA, Rosales-Serna R, Ibarra-Pérez FJ, Cazares-Enríquez B, Acosta-Gallegos JA, Ramírez-Vallejo P, Wassimi N, Kelly JD (1997) Improving common bean performance under drought stress. Crop Sci. 37: 43-50. Schussler JR, Westgate ME (1991) Maize kernel set at low potential. I. Sensitivity to reduced assimilates during early kernel growth. Crop Sci. 31: 11891195. Shen XY, Webster DB (1986) Effect of water stress on pollen of Phaseolus vulgaris L. J. Am. Soc. Hort. Sci. 111: 807-810. Turner NC, Jones MM (1980) Turgor maintenance by osmotic adjustment: a review and evaluation. In Turner NC, Kramer PJ (Eds.) Adaptation of Plants to Water and High Temperature Stress. Wiley. New York. Pp. 87-104. Vieira RD, TeKrony DM, Egli DB (1992) Effect of drought and defoliation stress in the field on soybean seed germination and vigor. Crop Sci. 32: 471-475. Zalewski K, Lahuta LB, Horbowicz M (2001) The effect of soil drought on the composition of carbohydrates in yellow lupin seeds and triticale kernels. Acta Physiol. Plant. 23: 73-78. OCT 2009, VOL. 34 Nº 10