Improvement of photosynthesis, gas exchange and chlorophyll content of bean by application of Epibrassinolide under drought stress condition

In order to study the photosynthesis, gas exchange and chlorophyll content of bean by application of Brassinosteroid, an experiment was conducted during 2016-2017 at the research farm of the University of Zanjan, in split factorial base on randomized complete block design with three replications. In this experiment, irrigation levels (in two levels of optimal irrigation and drought stress) were applied to main plots and bean cultivars (at two levels of Kusha cultivar and COS16 genotype) and different levels of Brassinosteroid (at four levels of 0, 2, 4 and 6 μM) were allocated to sub plots as factorial. In the flowering stage, by cutting irrigation, drought stress was applied and simultaneously with drought stress, bean plants, were sprayed with Brassinosteroid (Epibrassinolide) at the indicated concentrations. The results showed that drought stress had negative effects on the intercellular CO2 concentration, transpiration rate, stomatal conductance, photosynthesis rate and chlorophyll content, but with the elimination of drought stress and re-irrigation, the plants were recovered. The use of Epibrassinolide minimized the negative effects of drought stress on photosynthesis, gas exchange, chlorophyll content and seed yield of bean. The highest seed yield was obtained by application of 2 μM of Epibrassinolide (with an average of 2068.2 kg.h-1). Therefore, the use of this hormone can be suggested as a solution to increase drought stress resistance and increase the seed yield of bean under optimal irrigation and drought stress conditions.