Silk browning is related to cob color

Presence vs. absence of the polyphenol:polyphenol oxidase browning reaction of cut silks was found by C. S. Levings and C. W. Stuber (Genetics 49:491, 1971) to involve a dominant vs. recessive factor pair, which they designated Fv (ortho-dihydroxy flavonols present; browning) vs. fv (ortho-dihydroxy flavonols absent; non-browning). In families segregating 1:1 for cob color due to P-WR vs. P-WW in 1984 (grown for study of segregation of the expression of brown vs. white tassel glumes-see MNL 57:33, 58:75), segregation was noted for browning vs. non-browning silks. The browning-silk plants each showed brown color in the tassel glumes, and the non-browning plants none; cob colors in the harvested ears confirm that all plants with browning silks were P-WR (red cob, brown tassel glumes) and that all plants with non-browning silks were P-WW (white cob, white tassel glumes). The red:white ratios were, in families from five separate sources of P-WR backcrossed to A619 (P-WW), 6:10, 8:8, 11:5, 9:7 and 18:23. The inbred lines studied by Levings and Stuber and classified as Fv Fv (browning silks) were CI21, Hy2, L317, NC232, T61, T204 and WF9; all are P-WR, red-cob lines. Those classified as fv fi) were Kys, NC34, NC45 and NC236; the first and fourth are P-WW, white-cob lines; the other two may or may not be white, information being unavailable (the help of C. Stuber in tracking down some of the cob colors for which I had no information is appreciated).

The association of P-WR with silk browning due to ortho-dihydroxy flavones is consistent with the involvement of P-WR, as proposed by E. D. Styles and 0. Ceska (Phytochem. 14:413, 1975), in determining a key, early step in the flavone branch of the flavonoid pathway. All is not settled on the association, however, since it is clear that some white-cob lines have browning silks. Among 40 white-cob inbreds that were checked in 1984, 10 showed browning (yet had white tassel glumes, consistently with their cob color). Among these inbreds is Mo20W, for which a small backcross (P-WR/P-WW x P-WW) segregated red:white cobs (17:27), but all had browning silks. Thus, red cob appears to determine browning silks, while white cob determines non-browning silks only in most sources, not all.

Should browning in white-cob inbreds turn out to be related to the undesirable "smoky" colors in white field corn, browning of silks would be a simple and convenient means by which this tendency could be detected; in any event, if silks do not show browning when cut the indication at this time is that the cob will be white.

E. H. Coe

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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