Evaluation of black bean genotypes (Phaseolus vulgaris L.) under drought stress conditions

  Black beans are a variety of common beans (Phaseolus vulgaris) and belong to the legumes. Black beans contain a wide range of flavonoids, as well as some phenolic acids. The problems of production of this product, which reduces yields, are non-biological stresses, including drought. About 60% of the world's cultivateted bean is at risk of intermittent drought or at the end of the season. Several indices have been proposed to assess the response of genotypes under different environmental conditions and to determine their resistance and susceptibility, which helps to select drought tolerant genotypes. The aim of this study was to investigate the effect of drought stress on yield and yield components of black bean genotypes and to evaluate the response of these genotypes to drought stress by indices of drought tolerance. 14 bean genotypes including 11 black bean genotypes and 3 other genotypes (which were control genotypes) were obtained from the Gene Bank of Agricultural and Natural Resources department in Karaj in two completely randomized block designs with 3 replications in two adjacent plots In the educational research farm of Ilam University in the city of Mehran was cultivated. In the first experiment, irrigation was carried out as normal and irrigation intervals based on 50 ml evaporation from the evaporation pan. In the second experiment, water stress was applied at flowering stage. At this stage, the irrigation interval was based on 100 ml evaporation from the pan. The measured traits included number of pods per plant, number of seeds per pod, plant height, grain yield and 100 grain weight. After data collection, analysis of variance and mean comparison by LSD method were performed for the studied traits. In addition, in order to determine resistant and stress resistant cultivars, various indices related to stress resistance including SSI (stress susceptibility index), STI (stress tolerance index), TOL (stress tolerance index), MP (average productivity index), GMP (Geometric Productivity Indicator) and Harm (Harmonic Average Index) were calculated. In order to determine the best index, the correlation of genotypes yield under stress condition (YS) and without stress (YP) with drought tolerance index was calculated. The results of combined analysis of the data showed that the effect of environment and genotypes on all traits was significant and the diversity between the studied genotypes was observed in terms of traits under normal and stress conditions. In terms of yield, 1140 and 1170 genotypes had the highest and lowest yields respectively. In general, all traits were changed due to stress and their mean values decreased under stress conditions. The percentage of grain yield under stress was estimated to be 24.26%. The most changes due to drought stress in genotypes related to yield, pod number and plant height. The most changes were due to drought stress in yield, pod number and plant height of black bean genotypes. Based on the Principal Component Analysis on the six indicators, YP and YS in the genotypes evaluated, it was found that the two main components justify 98.9% of the total variation. The first component expresses 68.6 percent of the total variation. The highest positive factor in the linear composition of the first component was YP, YS, MP, GMP, and STI. Based on the analysis of the main components on the six indicators, YP and YS in the genotypes evaluated, it was found that the two main components justify 98.9% of the total variation. The first component expresses 68.6 percent of the total variation. The highest positive factor in the linear composition of the first component was YP, YS, MP, GMP, and STI. Based on the findings of this study, yield loss in drought stress conditions in black bean genotypes was mainly due to the reduction in the number of pods per plant. According to correlation of YS and drought tolerance indices, STI, GMP and MP were the best indices of drought tolerance under stress conditions. Therefore, based on these indices, among the genotypes of black beans, 1183 genotype as the most tolerant (with 8.07 g per plant) and genotypes 1187 and 1177 as the most sensitive genotype to drought stress (respectively, with yield 4. 17 and 5.22 g per plant) were selected. Also, control genotypes (256, Talash and Daneshkadeh) had higher yields (respectively 18.72, 13.56 and 14.21 g per plant respectively) and, for most of the indices, were more resistant than black bean genotypes. By using bi-plot of the Principal Component, genotype 1183 selected as the most tolerant drought stress.