Evaluation of agronomic traits changes in drought stress and their impact on the yield of mungbean cultivars and promising lines.
Mungbean (vigna radiata) is one of the important short-duration grain legume crops with wide adaptability, low input requirements and the ability to improve the soil by fixing atmospheric nitrogen and well suited to a large number of cropping systems and constitutes and important source of high quality protein in the cereal based diets of many people in Asia . Mung bean seeds are rich in protein and amino acids, thus serve as a valuable protein source for human consumption. Pods and sprouts of mung bean are also eaten as a vegetable and are a source of vitamins and minerals. Moreover, this plant is nitrogen fixing, has a short life cycle and therefore, is widely grown as mixed, inter crop or in rotation to improve nitrogen status of soil or to break the disease/pest cycles. Drought is a worldwide problem, constraining global crop production and quality seriously and recent global climate change has made this situation more serious. Water is a vital factor for plant growth and development. Water deficit, limits the growth, permanent or temporary, distribution of natural vegetation and the performance of cultivated plants more than any other environmental factors .Therefore, innovation are needed to increase the efficiency of use of the water that is available. One approach is the development of new irrigation scheduling techniques such as deficit irrigation, which are not necessarily based on full crop water requirement. Deficit (or regulated deficit) irrigation is one way of maximizing water use efficiency (WUE) for higher yields per unit of irrigation water applied . The grower must have prior knowledge of crop yield responses to deficit irrigation . Accurate water application prevents over or under irrigation. Over-irrigation wastes water, energy and labor, leaches nutrients below the root zone and leads to water logging which reduces crop yields. Under-irrigation stresses the plant resulting in yield reductions and decrease returns . Water stress affects almost all aspects of mungbean growth and development. This crop suffering water stress resulted in decreased seed yield, pod number, number of seed [pod.sup.-1] and 1000-seed weight. Supplemental irrigation, particularly at the pod filling stage to improve plant water status gives economic increase in yields in areas of super optimal temperature during the reproductive growth. The late flowering and pod setting stages appear to be the most sensitive stages to soil moisture stress. Mungbean yield was depressed when the irrigation treatments were given at flowering, with or without pre flowering irrigation (15).
Stress is a series of external factors that have a negative impact on a plant's life. Drought is one of the most effective stresses on plant's development and production because water deficit limits the photosynthesis, stimulates plant to produce more ABA that in turn induces more stomatal closure, increases water movement resistance in plants, changes leaf's energy output, decreases hydraulic conductivity and disrupts plant's thermodynamic temperature. Drought stress is often accompanied by heat stress that intensifies the effects of salinity on leaves and in the root zone because of transpiration decrease from the leaves surfaces that limits their cooling due to water vaporization. Dry matter production in plants in water limitation conditions depends on climate and soil status that affects available soil water and plant water use efficiency. Plants with higher water absorption capacities or higher water use efficiency, better tolerate drought conditions . Drought stress affects all plant's vital mechanisms and while stomatal and non-stomatal factors, together, play a role in photosynthesis reduction; one of these factors may have more influence over leaf's assimilation capacity depending on the severity and duration of the stress, and plant's growth stage . Drought stress directly makes drastic changes in LAI and therefore, severely decreases total photosynthesis due to its multiple effects on growth including limitation of leaf development. Leaf area is important because photosynthesis is a function of it. However, rapid development of the leaf area may have a negative effect on water availability in plants . Thus, drought stress reduces the biomass and despite slightly increasing the harvest index, it reduces production per unit area and this significantly decreases the number of pods, pod height, number of seeds per pod, seed length & diameter, and weight of 100 grains and ultimately reduces the seed yield.
Materials And Methods
This experiment was carried out during two years (2010-11) at experimental field of Safiabad Agricultural Research Center of Dezful, southwest Iran. This field has been located in a warm and semiarid region with hot summers and cool and relatively dry winters having low precipitations, 82.9 m above sea level in 48[degrees]26'N and 32[degrees]16'W, with 321 mm average 30 years rainfall, 2400 mm average annual evaporation, maximum temperature of 52[degrees]C and mean temperature of 23.9[degrees]C. This experiment was implemented using a complete randomized blocks split plot with three replications. Main factor included three irrigation levels at 120(I1), 180(I2) and 240 mm(I3) evaporation from the pan, while cultivars considered as the sub-factor comprised of five varieties namely Partow, Indian heap and vc6172, cn95 & kps1as promising lines. Traits evaluated included: seeds to pod ratio, number of pods per plant, number of seeds per pod, weight of 100 grains, yield per hectare, biomass, harvest index, leaf area index, grain length and diameter. Soil was a clay loam with a pH of 7.2, 0.096 ppm of organic matter, 960 ppm of total N, 14.3 ppm exchangeable phosphate, 140 ppm exchangeable potassium, and 1 milimos Ec. NPK were added at the rate of 50 kg N/hectare as ammonium nitrate 46% N, 60 kg P2O 5/hactar as superphosphate 15.5% PO (before sowing) and 0-90-180 kg K2 O/ha as potassium sulfate 48% K O at treatments fertility. The other agronomic practice for growing mungbean was followed as recommended. Representative samples were collected from three replicates for each treatment after 30-60 and 90 days from sowing, where leaf area index, Biomass, leaves and pods as well as weight of stem were determined. At harvest time, 20 guard plants were chosen randomly from each plot to determine yield attributes including number of pods/plant, seeds/pod, pods dry weight, and seed index. Whole plot was harvested to determine seed, straw, and biological yield/hectare. The obtained results were subjected to statistical analysis of variance according to the method described in Mastasc , and the combined analysis of the two seasons was calculated using the Sas method. Furthermore, mean comparisiosns performed using Dancan examination on 1% and 5% levels.
Results And Discussion
Seeds to pod ratio (SP):
Data analysis revealed that different cultivars had a significant effect (P [less than or equal to] 0.01) on seeds to pod ratio.The height sp (67%) was obtained in plots seeded with pa; while, the lowest sp (63%) was obtained from plots planted with Ih cultivar (Table 2). These results in Mungbean cultivar were also reported by Maqsood et al  and Siddique , identifying different sps in Mung bean cultivars.
Number of seeds per pod (S/P):
The results showed significant differences (p [less than or equal to] 0.01) in the drought stress levels to S/P. The maximum and minimum S/P was produced by I1(10) and I3(8.3). No significant difference was found between S/P cultivars. Furthermore, the results suggested a significant difference (p [less than or equal to] 0.05) in the interaction between drought stress and cultivars to S/P. The maximum and minimum S/P values were produced by I1 x pa (10.8) and I3 x kp (7.2) seed per pod, respectively.
Weight of 100 Grains (100GW):
Data analysis revealed that different cultivars had a significant effect (P [less than or equal to] 0.01) on 100GW. The heaviest (7.83 g) was produced in plots seeded with vc while; while, the lightest seeds (3.65 g) were obtained from plots planted with the pa cultivar (Table 2). The variation in 100GW among different Mungbean cultivars occurred due to varying potential cultivars for this parameter , an interaction between drought stress and cultivars to 100Gw. The maximum and minimum 100GW was produced by I2 x vc (8 g) and I3 x pa (3.6 g) 100GW, respectively. These results in Mungbean cultivar were also reported by Maqsood et al.  and Siddique , identifying different 100GW in Mungbean cultivars.
Number of pods per plant-1 (p/p):
The results indicated that the number of pods per plant-1 varied significantly (p [less than or equal to] 0.01) in different cultivars. The maximum and the minimum p/p(29.2 ,19)were observed in the cultivar vc and cn, respectively. Variation in p/p in Mungbean cultivar was also reported by Ahmad , Bismillah Khan,  and Sadeghipour .
Seed Yield (SY):
The cultivars showed significant differences (p [less than or equal to] 0.01) in their seed yield. The highest seed yield (3482 kg/h) was produced by Partow; while, the lowest seed yield (2287 kg/h) was recorded by Promising line kp.The maximum SY of cultivar pa was due to higher p/p and s/p. Further, the significant effect of seed yield had been reported by Ahmad , Bismillah Khan , and Sadeghipour . Drought stress levels, also, showed significant differences (p [less than or equal to] 0.01) in seed yield, in the manner that the maximum seed yield (3458kg/h) by I1, and minimum seed yield (2291kg/h) were recorded by I3.
Withholding irrigation caused a decrease in p/p and s/p and, thus, SY. These findings are quite in agreement with those of Nielsen and Nilson .Thomas et al .also reported that SY of Mungbean was reduced by 65% when water stress was imposed at flowering. Interaction effect between drought stress levels and cultivars was significant (p [less than or equal to] 0.01) in case of SY. The maximum SY (44365kg/h) was observed in I1 x Partow ; while, the minimum SY (1783kg/h) was produced in I3 x kps1(Table3).
Harvest Index (HI):
Significant differenes (p [less than or equal to] 0.01) were found in the drought stress levels, cultivars and interaction between drought stress and cultivars to HI%. The maximum (32.3%) HI was obtained by I2 and the minimum (23.5%) HI was obtaind by I1, the maximum (30.9%) cultivars for HI x vc, and minimum (24.9%), HI x cn. The results showed a significant difference (p [less than or equal to] 0.05) for interaction between drought stress and cultivars to HI. The maximum and minimum HI were produced by I2 x vc (36.7%) and I1 x cn (23.5%), respectively. The same results regarding HI of Mungbean cultivar was also reported by Abbasi et al.  and Ahmad , identifying different 100Gw in Mung bean cultivars.
The results revealed that different cultivars and drought stress levels and interaction between drought stress and cultivars had a significant effect (P [less than or equal to] 0.01) on Biomass. According to cultivars, the maximum B (14020kg/h) was produced in plots with vc; while, the minimum B (10500kg/h) was obtained from plots planted with cn cultivar (Table 2). The variation in B among different Mungbean cultivars occurred due to varying potential cultivars for this parameter . According to drought stress, the maximum B (16166kg/h) was produced in plots with I1; while, the minimum B (10322kg/h) was obtained from plots planted with I3 (Table2). For interaction between drought stress and cultivars to B, the maximum and minimum B were produced by I1 x vc (19390k g/h) and I3 x kp (7503kg/h) B, respectively. These results were also reported by Abbasi et al.  and Sadeghipor et al. .
Leaf Area Index (LAI):
The drought stress showed that cultivar treatments, drought stress, and interaction had a significant effect (P [less than or equal to] 0.01) on Leaf Area Index. According to cultivars, the largest LAI (5.807) was obtained using Ih; while, the minimum LAI (5.137) was obtained from plots planted with kp cultivar (Table 2). According to drought stress, the maximum LAI (8.023) was produced in I1; while, the minimum LAI (3.641) was obtained from plots planted with I3 (Table 2). For interaction between drought stress and cultivars to LAI, the maximum and minimum LAI was obtained by I1 x Ih (8.577) and I3 x kp (1.953) LAI, respectively. These findings are quite in agreement with those of Nielsen and Nilson . Thomas et al .
Shortage of water causes interferences in the biochemical activities, production of photosynthetical materials, shortage of seed capacity, reduction of seed size, and, ultimately, a decrease in seed yield. The results of this study indicated that drought stress has an in/direct effect on plant vital processes, inflicting its life. Accordingly, optimal conditions for production would be watering the plant at 120 mm evaporation level from the pan. Furthermore, each attribute was found to have a direct and significant effect on seed yield, indicating that all the attributes, that is, P, HI, LAI, and B should be controlled; otherwise, the plant growth would be impaired. Likewise, differences were found in the tolerance to stress level between the cultivars and lines; however, this attribute ranked lower compared to Partow cultivar due to seed size, better marketability, indeterminate growth, and VC seed attrition. Compared to Partow cultivar (about 8%), the atrition level was found to be lower (2%) for the promissing line, and mechanized harvesting can be performed in the area. These findings were compatible with, Ahmad , Bismillah Khan , Maqsood et al , Nielsen and Nilson  and Thomas et al. .
seeds to pod ratio (SP), Weight of 100 Grains (100GW), Seed Yield (SY), Leaf Area Index (LAI), Harvest Index (HI), Biomass (B), number of pods per plant (P/P), number of seeds per pod (S/P), Cultivars: Partow(Pa),Indian heap(Ih), Promising lines: Vc6172(Vc), Kps1(Kp) and Cn95(Cn).
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(1) Zarifinia, Nasser, (2) Amir Aynehband, (3) Shahram Lak, (4) Adel Modhej, (5) Ali Akbar Ghanbari & (6) Reza Sekhavat
(1) PhD. student of physiology, Islamic Azad University, Science & Research branch in Khuzestan;
(2,3,4) Professor of Science and Research branch of Khuzestan;
(5) Researcher in Seed and Plant Improvement Institute, Karaj, Pulse crops department;
(6) Researcher in Safiabad Agricultural Research Center of Dezful
Zarifinia, Nasser, PhD. student of physiology, Islamic Azad University, Science & Research branch in Khuzestan
Table 1: Interaction effects of water stress levels and cultivar on agronomic traits of mungbean (2010-2011) Variation Df Sp 100Gw SY/h LAI source Y(Year) 1 50.5ns 1.003ns 226402ns 5730490 ** Rep x Y 4 11.6ns 0.275ns 92195ns 983628ns A 2 17.8ns 0.777 * 10446092 ** 185513134 ** A x Y 2 0.0001ns 0.0001ns 128.6ns 9302.5ns A x rep x Y 8 27.9ns 0.187ns 176791ns 1303663ns B 4 41.6 * 55.7 ** 421375 ** 4561791 ** A x B 8 29.01ns 0.502 ** 1705110 ** 31463958 ** Y x B 4 0.0001ns 0.0003ns 132.9ns 24365ns Y x A x B 8 0.0001ns 0.0009ns 67ns 26365ns Error 48 16.43 0.225 236293 970495 CV% 0.062 0.0757 0.1661 0.1912 Variation Df HI% B(kg/h) S/p P/P source Y(Year) 1 22.5ns 56250ns 4.14ns 2.88ns Rep x Y 4 2.16ns 51837ns 0.026ns 10.85ns A 2 537.9 ** 3443441 ** 20.84 ** 70.02 * A x Y 2 0.0001ns 0.001ns 0.0008ns 0.0005ns A x rep x Y 8 4.79 4441ns 0.448ns 11.12ns B 4 144.8 ** 558409 ** 1.65ns 280.89 ** A x B 8 87.6 ** 174220 ** 1.79 * 18.82ns Y x B 4 0.0001ns 0.001ns 0.171ns 0.0032ns Y x A x B 8 0.0001ns 0.001ns 0.109ns 0.0006ns Error 48 6.61 21371 0.741 17.02 CV% 0.092 0.1177 0.0944 0.1695 Significant probability level of 5% and 1% *, **--insignificant ns--water stress A--cultivar B--interaction between water stress and cultivar AB Table 2: Mean comparison of yield and yield components of mungbean cultivar grown under water stress levels conditions (Average values of 2010 and 2011 seasons) Treatment Sp (%) S/p p/p 100G w (g) SY(Kg/h) I1 64.5a 9.5b 24.3ab 6.5a 3458a I2 66a 9.4b 25.9a 6.3ab 3300b I3 65.5a 10a 22.8b 6.1b 2291c Partow 67a 10.04a 26.3b 3.68d 3482a Hendi 63b 10.03a 25.4b 5.19c 3271ab Vc6172 66.1a 8.03c 29.4a 7.83a 2978b Kps1 64.7ab 7.73c 21.2c 7.22b 2287d Cn95 65.9ab 9.4b 19.6c 7.36b 2614c Treatment LAI HI% B(kg/h) I1 8023a 24c 16330a I2 3758 32a 1061b I3 3676b 28b 1033b Partow 5208a 25c 13410a Hendi 5806a 27b 13650a Vc6172 5305a 31a 14020a Kps1 5137a 31a 10510b Cn95 4404b 25c 10500b Table 2: Mean interaction comparison of agronomic traits of mungbean cultivar grown under water stress levels conditions (Average values of 2010 and 2011 seasons) Treatment S p(%) S/p P/P 100Gw (g) I1 xPa 64.4a 9ab 28.4ab 3.7d I1xIh 63a 9.6a 25.6b 5.2c I1xvc 68.5a 7.8c 28.7ab 7.6a I1xKP 60.8a 8.4b 19.8c 6.6b I1xcn 65.8a 9.7a 18.9c 7.3a I2x Pa 68.8a 10.3a 25b 3.7d I2xIh 64a 9.8a 26.9ab 5.3c I2xvc 65.5a 8b 33.3a 8 a I2xKP 67.3a 7.2c 23.4b 7.7a I2xcn 65.9a 8.7ab 21.1c 7.1a I3x Pa 67.9a 10.8a 25.1b 3.6d I3xIh 62.2a 10.7a 23.7b 5.1c I3xvc 64.3a 8.3b 26.2ab 7.9a I3xKP 66a 7.6c 20.4c 7.4a I3xcn 66a 9.7a 18.8c 7.7a Treatment SY(Kg/h) LAI HI% B(kg/h) I1 xPa 4365a 4978c 21e 17440a I1xIh 3045b 8577a 25de 17000a I1xvc 3789ab 7904a 25de 19390a I1xKP 2964b 3464c 24de 15990ab I1xcn 3124b 6194b 24de 11800b I2x Pa 3626ab 6517b 27d 11350b I2xIh 4160a 4312c 28d 13490b I2xvc 3031b 3919c 37.4a 11540b I2xKP 2114c 1846e 37b 8020e I2xcn 2550c 2188d 27d 9130d I3x Pa 2455c 3830c 28d 11450b I3xIh 2607c 3521c 29d 10460c I3xvc 2113c 4094c 27d 11120b I3xKP 1783d 2103d 31c 7500d I3xcn 2168c 4830c 25de 10560c Table 12: Correlation coefficients between examined traits in mung bean cultivars Seed HI(%) LAI B(kg/h) [pod-.sup.1] HI% 0.331 ** LAI 0.480 ** 0.433 **- Biomass 0.516 ** 0.504 **- 0.678 ** 100 seed w(g) -0.014ns 0.332 ** 0.141ns 0.248 **- SP(%) 0.051ns- 0.113ns 0.322 **- 0.027ns p/p 0.0277ns 0.317 ** -0.0187ns 0.371 ** Seed Yield 0.077ns 0.307 ** 0.385 ** 0.658 ** (kg/h) 100s w(g) SP(%) p/p HI% LAI Biomass 100 seed w(g) SP(%) 0.044ns p/p -0.615ns 0.132ns Seed Yield 0.388 **- 0.325 ** 0.715 ** (kg/h)
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Zarifinia; Nasser; Aynehband, Amir; Lak, Shahram; Modhej, Adel; Ghanbari, Ali Akbar; Sekhavat, Reza|
|Publication:||Advances in Environmental Biology|
|Date:||Aug 1, 2012|
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