Segregation of red vs. white color in cob and tassel glumes

E.H. Coe has reported a correspondence between brown tassel glumes and red cob color (MNL 57:33, 58:75, 59:40). Pigmentation in both tissues is apparently controlled by the P locus, which also controls pericarp color. Coe indicates that in most families which are segregating for red vs. white cob color (P-WR vs. P-WW), plants with brown tassel glumes produce red ears, and plants with white tassel glumes produce white ears.

Plants carrying the P-VV allele produce ears with variegated pericarp and cobs, and white tassel glumes. P-VV has been shown by Brink and others to result from the presence of the transposable element Mp (equivalent to Ac) at the P locus. Mutations of P-VV to P-RR arise by excision of Mp to restore P-RR, resulting in red pericarp and cob. It was of interest to examine the segregation of cob and tassel color in the progeny of a plant carrying a P-RR allele derived as a mutation from P-VV. A plant carrying the revertant P-RR allele heterozygous with P-WW was selfed and progeny were scored for colors of tassel glumes and cob. Fourteen plants with brown tassel glumes produced red pericarp, red cob ears; 7 plants with white tassel glumes produced white pericarp, white cob ears. In this case, reversion restored P expression in the tassel glumes as well as pericarp and cob.

The correlation was also tested with another P allele known as P-Quebec36. This allele conditions a faint red pericarp, red ear phenotype. A plant of genotype P-Quebec36 ts2/P-WW + was selfed (ts2, situated 2 map units distal to P, determines a tassel seed phenotype.) Progeny grown from this self comprised 16 with normal tassels, and 5 with the tassel seed character. Of the plants with normal tassels, 10 had brown tassel glumes and produced red cobs, while 2 had white tassel glumes and produced white cobs. No attempt was made to score tassel glume color on the tassel seed plants, but these produced red ears. Ears from the remaining plants were lost.

Thus, in these 2 small F2 families, pigmentation of tassel glumes and cob was always correlated. (This material is based upon work supported by the National Science Foundation under a grant awarded in 1984).

Thomas A. Peterson

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