Response of pinto bean cultivars to water deficit at reproductive stages.

A field experiment was conducted in 2008, to investigate the effects of different irrigation treatments (I 1 , I 2 , I 3 and I 4 ), well-watering on the bases of 70 mm evaporation from class A pan and irrigation disruptions at flowering stage, grain filling stage and during flowering and grain filling stages, respectively) on yield and yield components of three pinto bean cultivars (Talash, Khomain and COS 16 ). The experiment was arranged as split-plot based on randomized complete block design in 3 replications, with the irrigation treatments in main plots and pinto bean cultivars in sub-plots. Percentage and duration of ground green cover, leaf chlorophyll content index, plant biomass, grains per plant, mean grain weight and grain yield per unit area decreased, due to water stress at reproductive stages. Reduction in grain yield increased with increasing duration of water limitation. Talash had more but smaller grains per plant, while Khomain produced less but larger grains, compared with other cultivars. Consequently, grain yields of Talash and Khomain were almost similar. Grain yield of COS 16 was 10.4% and 11.6% less than that of Talash and Khomain, respectively. However, this difference was not statistically significant. Although harvest index of pinto bean cultivars varied with variation in irrigation treatments, it was not significantly affected by irrigation disruption and cultivar. In general, it was detected that irrigation is critical during flowering and pod filling phases in order to improve grain yield of pinto bean cultivars.