Phenotypic recurrent selection in ideotype breeding of pinto beans

Summary

Plant growth habit (type) plays a major determining role in the acceptance of a dry bean cultivar by commercial growers. Under the threat of wet fall conditions in the midwestern U.S., growers show a preference for upright plant types-I and II over the more prostrate type-III growth habit of commercial pinto cultivars. The prostrate habit creates considerably more risk of harvest losses and potential of white mold (Sclerotinia sclerotiorum) development during a wet growing season.

The breeding strategy being utilized to develop better adapted pinto bean cultivars for the humid midwest is based on the concept of ideotype breeding which has been successfully applied to small seeded navy and black beans. A system of phenotypic recurrent selection using S₁ selection is being followed in order to recombine desirable traits from two diverse germplasm pools. One germplasm pool possesses the desirable architectural plant form and disease resistance traits of the small-seeded types while the medium-seeded germplasm source possesses the desirable seed size, shape and color characteristics of the pinto class. Since a repulsion phase linkage appears to exist between type-II architecture (architype) and medium seed size (40 g/100 seeds), recurrent selection is shown to be the most effective procedure for breaking up undesirable linkage groups and for increasing the frequency of desirable genes, thus enhancing the chance for the desirable genetic recombinations to occur.