Effect of water supply on seed quality development in common bean (Phaseolus vulgaris var.)

In order to determine the best developmental stage of three common bean cultivars (Talash, COS16 and Khomain) at which maximum seed quality is attained under different irrigation regimes (I-1-irrigation after 60 mm, I-2-irrigation after 80 mm and I-3-irrigation after 100 mm evaporation from class A pan), a split plot experiment (using R.C.B. design) with 3 replications was conducted in 2004 at the Research Farm of the Faculty of Agriculture, Tabriz University, Tabriz, Iran. Seeds were harvested at five day intervals in nine stages. Analysis of variance of the data indicated that maximum seed weight, percentages of viable seeds and normal seedlings, seedling dry weight and minimum electrical conductivity of seeds were not significantly different among seeds produced under different irrigation conditions. However, maximum seed weight and minimum electrical conductivity were significantly affected by the cultivars. Maximum seed weight of Khomain was significantly higher than that of Talash and COS16. The lowest and the highest minimum electrical conductivity were obtained for Khomain and Talash, respectively, but this was not significantly different between Khomain and COS16. Changes in seed quality during development and maturity showed that mass maturity and maximum seed vigor under I-3 occurred earlier, compared to other two irrigation regimes. Mass maturity under I-1 and I-2 achieved at about 1270 degree-days after sowing for Talash and 1210 degree-days after sowing for COS16 and Khomain. Mass maturity of all cultivars under I-3 occurred at about 1160 degree-days after sowing. Maximum quality of common bean seeds was attained some times after mass maturity, when seed moisture content was about 16-25%. Seed vigor of all treatments was reduced, as harvests delayed. Therefore, seed quality of pinto bean cultivars under different irrigation regimes coulde be improved, if seeds harvested slightly after mass maturity.