The red common bean (Phaseolus vulgaris L.) seedcoat colors produced by the dominant gene R and the dark red kidney gene rk(d) 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 rk(d) and oxblood controlled by R, Twenty bean varieties and breeding lines were test crossed with genetic tester stocks c(u) 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 F-1 progenies from the test crosses demonstrated that unambiguous identification of the genotypes of the two dark red colors could be achieved using the c(u) 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 rk(d), 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: c(u) b v rk BC1 5-593 x b v BC3 5-593 and c(u) b v rk BC1 5-593 x c(u) BC3 5-593. Classification of the F-2 progenies demonstrated that the c(u) gene does not entirely prevent rk red color from being modified by V. The interactions of rk, rk(d), and R with C,c(u), G, B, and V are discussed, and previous literature concerning those interactions is critically reviewed.
