Selection for increased percentage phaseolin in common bean : 2. Changes in frequency of seed protein alleles with S1...

Recurrent selection methods are designed to increase the frequency of favorable alleles within a population(s) with each cycle of selection. Yet it is likely that different methods will change allele frequencies at different rates or may act on different alleles. To investigate the ability of S1 family selection to shift the frequencies of favorable alleles within a population of Phaseolus vulgaris (L.), we examined the changes in frequencies of six alleles (Phas (S) , Phas (C) , Phas (T) , phas (-), lec (-), and Arc1 (+)) that affect the amount of phaseolin accumulated in seeds, over three cycles of selection for increased percentage phaseolin (PPS). The frequency of alleles Phas (C) and lec (-), both of which have positive effects on percentage phaseolin, increased with selection while the frequencies of phas (-) and Arc1 (+), which have strong negative effects, decreased. The frequencies of the Phas (S) and Phas (T) alleles showed no linear trends with selection, indicating that the frequency changes may be due to random drift and not to the selection procedure. The proportion of the phenotypic variation (R (2)) for percentage phaseolin that was explained by each of the alleles, and by all the alleles combined, changed with each cycle of selection. In most cases the change resulted in a decrease in the R (2) value. In this population, S1 family selection was effective at increasing the frequencies of all favorable alleles except Phas (T) , and rapidly decreased the frequencies of deleterious alleles.