C.S. Levings and C.W Stuber (Genetics, 1971) showed that browning of cut ends of silks of inbred lines T61 and NC232 is under monogenic control in crosses and backcrosses with Kys and NC236. In MNL 60:50 and 59:40, we suggested the control of silk browning by the P locus, based on the observation that the cob color of P locus and silk browning were not separated by genetic recombination. White cob and browning inbreds that we tested further are the following: K44, K166, Ky228, Mo1W, Mo14W, 79-R1141, 79-R1193, Mo22, and K64. Interestingly, one plant of 15 F2 progeny was nonbrowning, red cobbed from the cross of browning, red cobbed W23 to 79-R1193, one of the white cob and browning inbreds. This indicates the possibility that the phenotypic expressivity of silk browning, mediated by the P locus, could be dependent on genetic background or be labile to physiological conditions. We are conducting further genetic examination of those possibilities.
To further examine whether browning of silks in those white cobbed inbreds results from possible involvement of a duplicate factor separable from the P locus or from allelic relationship, we intercrossed silk browning, white cob inbreds and selfed the progeny.
All but one of the F1 progenies, and all but three of the F2 progenies, showed only browning silks. Since silk browning is a dominant character, 1 nonbrowning plant out of 21 F1 progeny of K44/79-R1141 could be due to seed contamination or to low expressivity resulting from physiological conditions. The same explanations could apply to nonbrowning plants of F2 progeny of K44/79-R1141, 79-R1193/Ky228, and K44/Ky228 (3 out of 36, 2 out of 47, and 1 out of 23, respectively). All F2 progeny of 79-R1141/ Ky228 and 79-R1141/79-R1193 showed silk browning, but F2 data for K44/79-R1193 and Ky228/79-R1141 are not available. These observations favor the conclusion that the determinant of browning of cut ends of silks, which was not separable from the P locus by genetic recombination, is of allelic relationship, even though larger samples are needed for more tests.
Chang-deok Han and Ed Coe
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