When a white endosperm y1 line is crossed to a Y1 line and the F1 is selfed, it is very common to find a pale yellow kernel phenotype segregating 3:1 pale yellow : white among the y1 class of the F2. The genetics of this phenomenon has not been reported upon. Because the phenotype of the pale yellow kernels is similar to that of Bn1 (Brown aleurone1, accumulation of yellow pigment in the aleurone layer, most easily seen on white endosperm backgrounds), an allelism test was conducted between one of these unknown pale yellow aleurone factors and Bn1. The particular pale yellow aleurone allele chosen for this test, Bn*-PSS, came from a rgd1 y1 stock that had been crossed to our M14/L317 standard lines a few generations previously, followed by several generations of selfing, and was now homozygous for pale yellow aleurone on y1 endosperm. The homozygous y1 Bn*-PSS line was crossed to the Maize COOP's y1 Bn1 line, and the F1 was backcrossed by a homozygous y1 bn1 line. All of the kernels on the backcross ears were pale yellow, indicating either allelism or tight linkage of the two mutants. Since the number of kernels on the ears was rather large (n = 3,799), the mutants are most likely allelic. Bn*-PSS has been redesignated Bn1-PSS.
When working with y1 and other endosperm carotenoid mutants, it is desirable to have a genetic background that is free of factors that obscure the mutant phenotype. The pale yellow aleurone color present in Bn1 mutant kernels can sometimes mask the mutant phenotype of certain carotenoid mutants, such as y9, that are only slightly paler than the nonmutant yellow endosperm phenotype. Thus, the COOP is undertaking a survey of some of its more commonly used inbred lines to determine which ones carry Bn1. The lines under study are A632, A636, B73, B77, B79, H99, M14, Mo17, Oh43, Q66, Q67, W22, and W23. The inbred lines were crossed by y1 Bn1, and the F1's will be crossed by a y1 bn1 and the ears scored for Bn1 segregation vs. Bn1 homozygosity. The results should be ready in time for next year's Maize Newsletter.
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