Common bean (Phaseolus vulgaris L.) plant introduction 527829 (formerly Lamprecht M0048) has dark seal-brown (DSB) seedcoats and pink flowers. An investigation was conducted to determine the genotype of DSB seedcoat color. M0048 was crossed with Florida breeding line 5-593, which has genotype P [C r] D J G B V Rk. A series of crosses involving M0048, 5-593, and three genetic tester stocks (v BC2 5-593, cu BC2 5-593, and b v BC2 5-593) led to determination of the genotype. Data analysis indicated that M0048 has the genotype P [? R] J G B vlae, where DSB color is produced by the interaction of R with B. Crosses between [? R] and testers with [C r] always produced seedcoat mottling in F1, except where V masks the effect. The cross [? R] B v (DSB) × cu BC2 5-593 (cartridge buff seedcoat) produced marbled seedcoats (black/cartridge buff) with genotype [? R]/[cu?] B V. No way was found to determine whether the mottled or marbled seedcoat patterns were controlled at C or R; hence, the allelic ambiguity is indicated with a question mark. Illustrations are provided showing the difference between seedcoat mottling (a highly variable low-contrast patterning) and seedcoat marbling (a less variable high-contrast patterning, usually with cartridge buff as the background color). The development of a new genetic tester stock, [? R] b v BC3 5-593, was described, where [? R] b v gives unpatterned dominant red seedcoat color.
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