Effects of deficit irrigation on yield and yield components of pinto bean genotypes in Shahrekord

Introduction Pinto bean (Phaseolus vulgaris L.) is one of the most important bean types in Iran. Cultivation area of pinto bean is about 50% of total bean cultivation area and more than half of grain bean production belongs to this type of bean. Drought is the most important environmental stresses that affects agricultural production in arid and semiarid areas and reduces crop productions. According to FAO reports, 90% of cultivation area in Iran is under arid and semi-arid conditions, so water deficit severely affects crop quantity and quality of most crop. About 60% of bean cultivation area in the world are faced with drought. Bean yield loss due to drought stress depends on severity and duration of stress and genetic variations of genotypes. Bean yield components such as grain weight, grain number per plant and pod number per plant decrease by drought stress. According to the 15 bean genotypes evaluation in favorable moisture conditions and water deficit, there were significantly differences between genotypes for most of yield related traits. Due to limited water resources in the Iran, evaluation of bean genotypes under water stress is important. So this study was conducted to evaluate the changes in yield and yield components of pinto bean genotypes under deficit irrigation conditions. Material and Methods An experiment as split plot in randomized complete block design base was conducted for evaluation of effect of deficit irrigation at three levels (supply of 100, 80 and 60 percent of crop water requirement as main plot) on pinto bean genotypes in five levels (Taylor, Sadri, C.O.S.16, KS21193(Koosha193) and KS21486 as sub plot) in Shahrekord university. Before planting, seeds were disinfected with Benomyl fungicide. Then planting was conducted in 30 plant m-2 density.Crop water requirements calculated by Penman-Monteith equation amended by FAO. Irrigation treatments was applied at beginning of V4 stage (unfolding of third trifoliate leaf) and continued in the growing season. At the end of experiment one square meter of each plot harvested and yield and yield components were measured. Data were analyzed in SAS software (version 9.1). Slicing method was used for interaction mean comparison. Results&Discussion The effects of irrigation regime, genotype and the interaction of irrigation regime and genotype on unfertile pod number, unfertile pod weight, Fertile pod number, fertile pod per plant, grain number, grain weight, biological yield, grain yield and harvest index were significant. COS16 had the greatest fertile pod number and weight per unit area in supply of 100% of crop water requirement condition. Sadri and KS21486 had the highest and lowest percentage of reduction in the number of fertile pods per unit areain supply of 80% of crop water requirement conditionrespectively. Supply of 100 and 80 percent of water requirement conditions COS16 resulted in greatest grain number m-2. But this genotype did not produce grain by supply of 60% of water requirement condition. Reducing the amount of irrigation water reduced grain weight differently. KS21486 showed 12.8% and 26.5% reduction in grain weight in supply of 80 and 60 percent of crop water requirement conditions, respectively. While COS16 showed 47.1% and 100% reduction in grain weight in supply of 80 and 60 percent of crop water requirement conditions, respectively.Reducing the amount of irrigation water reduced genotypes grain yield. Grain yield of KS21486 decreased by 20.5% and 55.4% in supply of 80% and 60% of crop water requirement conditions, respectively. While KS21193 showed 68.5% and 93.2% grain yield reduction in 80% and 60% of crop water requirement condition, respectively. The highest seed yield by supply of 100 and 80% of plant water requirement condition was observed in C.O.S.16 (594.6 and 289.2 g.m-2 respectively), while C.O.S.16 in supply of 60% of plant water requirement did not produce seed. In supply of 60 percent of plant water requirement condition KS21486 had highest seed yield (109.5 g.m-2). Conclusion Grain number is more sensitive than grain weight to water deficit condition. Grain number reduced with greater intensity rather than grain weight reduction. In optimum irrigation and moderate water deficit condition C.O.S16 and in severe water deficit condition KS21486 produced more grain than the other genotypes.