EFFECT OF SELECTION FOR POLLEN GRAIN-SIZE ON VARIOUS TRAITS IN COMMONBEAN

Selection among microgametophytes usually exploits variation in pollen grain germination. Studies of variation in pollen grain size in commo n bean (Phaseolus vulgaris L.) suggested that selection for size might lead to changes in sporophytic traits. To determine whether microgame tophytic selection based on size would affect pollen grain size in sub sequent generations or sporophytic traits that were correlated with po llen grain size, pollen grains from three crosses were separated into two size categories by sieving and then used to pollinate cv. Diacol C alima. Selection resulted in changes in pollen grain diameter for poll en from F-1, F-2 and F-3 plants for all crosses. In vitro germination indicated no differences between vigor of large and small grains, but extraction and sieving reduced germinability. F-1 seed from two of the crosses with size-selected pollen varied in weight according to polle n grain size, but in subsequent generations, the effect disappeared. B oth size categories of selected pollen resulted in F-2 progeny with re duced numbers of seeds per pod as compared to controls, suggesting tha t the size selection process may have resulted in indirect selection f or traits reducing seed set. The overall results suggested that genes determining pollen grain size in bean have little or no effect on spor ophytic traits such as seed size and seed yield.