A Test Cross Protocol for Determining the Genotype of Dark Red Seedcoat Colors in Common Bean

Abstract

The red common bean (Phaseolus vulgaris L.) seedcoat colors produced by the dominant gene R and the dark red kidney gene rkd are very similar, making it difficult for breeders of red bean varieties to know which genotype is in their materials. A protocol employing test crosses with genetic stocks having known genotypes for seedcoat colors was developed to identify genotypes with either of two very similar dark red seedcoat colors: garnet brown controlled by rkd and oxblood controlled by R. Twenty bean varieties and breeding lines were test crossed with genetic tester stocks cu BC3 5-593 and b v BC3 5-593, and four of the varieties were test crossed with [? R] b v BC3 5-593. Analysis of the seedcoat colors and patterns in the F1 progenies from the test crosses demonstrated that unambiguous identification of the genotypes of the two dark red colors could be achieved using the cu BC3 5-593 and b v BC3 5-593 testers. The dark red color (garnet brown) of the Small Red market class materials was demonstrated to be produced by rkd, and the dark red color (oxblood) of `Jacobs Cattle' was demonstrated to be produced by R. A Light Red Kidney market class stock was derived from `Redkloud' and used in two crosses: cu b v rk BC1 5-593 × b v BC3 5-593 and cu b v rk BC1 5-593 × cu BC3 5-593. Classification of the F2 progenies demonstrated that the cu gene does not entirely prevent rk red color from being modified by V. The interactions of rk, rkd, and R with C, cu, G, B, and V are discussed, and previous literature concerning those interactions is critically reviewed.