The effect of drought stress on some of morphological and physiological traits of common bean (Phaseolus vulgaris L.) genotypes

Common bean (Phaseolus vulgaris L.) is the most important food legume and is an important source of calories, protein, dietary fiber, and minerals for human nutrition. In addition, it provides an essential source of protein for more than 300 million people worldwide including Iran. Drought is one of the most important abiotic stress factors that limits plant growth and results in significant seed yield reductions in around 60% of global bean production areas. Acclimation to water deficit in crops is the result of a series of integrated events. Upon exposure to drought stress, plants exhibit a wide range of responses at the whole-plant, cellular and molecular levels. At the whole-plant level, the effect of drought stress is usually perceived as a decrease in photosynthesis and growth, which is associated with alterations in carbon and nitrogen metabolisms. The reduction in the photosynthetic activity is due to several coordinated events, such as stomatal closure, chlorophylls cleavage and the reduced activity of photosynthetic enzymes. Stomatal closure is probably the most important factor controlling carbon metabolism, but the relative role of other limitations on photosynthesis depends on the severity of water deficit. The aim of this experiment was to determine the effect of different moisture stress levels on morph-physiological attributes of three common bean genotypes.

In order to evaluate the effect of moisture stress on some morphological and physiological traits of common bean genotypes, a greenhouse experiment was conducted as factorial design. The experimental factors included irrigation (100% FC; as control, 75% FC; as moderate drought stress and 50% FC; as severe drought stress) and three common bean cultivars (Saleh, Talash and Khomein). The experiment was performed at FUM (Ferdowsi University of Mashhad) glass house in 2015 with three replications. Pots (diameter 20 cm, height 30 cm) were filled with ten Kg of loamy soil and five seeds were planted in each of them. After emergence and establishment of seedlings, two plants were remained in each pot. Irrigation treatments were started at 4th leaf stage and continued up to the end of experiment. Plant height, stem diameter, shoot and root weight, root/shoot ratio, greenness, leaf relative water content, electrolyte leakage, stomatal conductance, biological and seed weight were measured. Data were analyzed using SAS software and least significant difference test (LSD) was used for mean comparisons at 0.05 level in MSTATC software.

The effect of Irrigation and genotype on plant height, shoot and root weight, chlorophyll at reproductive stage, relative water content, electrolyte leakage and stomatal conductance were significant. Also the interaction effect of irrigation×genotype on root/shoot ratio was significant. Drought stress decreased plant height by 8% and 21.4% in moderate and severe drought stress respectively. Shoot weight decreased by 30.1% (moderate drought stress) and 70.1% (severe drought stress) and root weight decreased by 48.9% (moderate drought stress) and 73.8% (severe drought stress) compared to control. The root/shoot ratio decreased under moderate drought stress in all genotypes but under severe drought stress, root/shoot ratio were increased in Talash and Khomein genotypes. Drought stress decreased chlorophyll content, so that under moderate and severe drought stress chlorophyll content decreased by 12.4% and 31.3%, respectively compare to control. Among genotypes, Saleh accumulated higher leaf chlorophyll content. The relative water content and stomatal conductance declined under drought stress treatments but electrolyte leakage was increased under drought stress treatments. Relative water content decreased by 9.9% and 30.7% under moderate and severe drought stress conditions, respectively compared to control. Under moderate and severe drought stress conditions stomatal conductance reduced by 33.3% and 53.3% respectively compared to control. Electrolyte leakage increased by 24.7% under moderate drought stress condition and 37% under severe drought stress condition compared to control. Also higher relative water content, stomatal conductance, and lower electrolyte leakage was observed in Saleh genotype. The highest seed yield among cultivars was found in Saleh and the highest seed weight was observed in complete irrigation regime.

Based on our results, Saleh genotype produced more seed, biomass, relative water content, chlorophyll, stomatal conductance and lower electron leakage, therefore, it seems that this genotype is more tolerant to moisture stress. However, generally, bean plant seems susceptible to drought, and it might not be feasible to impose high levels of drought stress on this crop.