Among light red and dark red kidney common bean (Phaseolus vulgaris L.) varieties, pink seedcoat color (light red kidney) is dominant to dark red, but when Red Mexican varieties (with dark red seedcoats) are crossed with dark red kidney varieties, dark red seedcoat is dominant to the pink segregants observed in an F2 population. A genetic investigation of this reversal of dominance was performed by making crosses in all combinations among standard varieties of the four recessive-red market classes—Light Red Kidney `California Early Light Red Kidney', Pink `Sutter Pink', Red Mexican `NW 63', and Dark Red Kidney `Montcalm'—and observing segregation for seedcoat colors in F2 and F3 progenies. The data were consistent with the hypothesis that `NW 63' carries a new allele at Rk, viz., rkcd, where cd stands for convertible dark red kidney. Thus, C rkcd expresses dark red kidney seedcoats and curkcd expresses pink seedcoats. Also, C B rkcd expresses garnet brown seedcoats, whereas C B rkd expresses liver brown seedcoat color. Thus, we propose the gene symbol rkcd for the Rk locus gene in `NW 63'. The rk gene from Light Red Kidney `Redkloud' and `Sutter Pink' was backcrossed (with cub v) into the recurrent parent 5-593, a Florida dry bean breeding line with seedcoat genotype P [C r] J G B V Rk. In the F2 progenies of BC2 to 5-593, the cub v rk segregants from `Redkloud' gave true pink seedcoats, whereas those derived from `Sutter Pink' gave consistently very weak pink color under humid Florida growing conditions. We propose the gene symbol rkp, where p stands for pale pink, for the distinctive rk allele in `Sutter Pink'. The more general implications of the above findings were discussed.
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