--Brent Buckner and Philip S. Stinard

The white cap locus (Wc) is a dominant gene which conditions white endosperm in a homozygous recessive y1 background or pale yellow endosperm with a white crown in the presence of Y1. The inbred line A188 also carries a dominant gene for white endosperm which exhibits phenotypically similar epistatic interactions with the y1 locus. We have conducted experiments to determine the allelic constitution of A188 for the y1 locus and also to determine if the dominant white gene in A188 is allelic to Wc.

To determine the allelic constitution of inbred line A188 for the y1 locus, we crossed A188 plants to plants that were homozygous for both the Y1 allele and the recessive wildtype wc allele (Y1/Y1, wc/wc). The progeny kernels from this cross were all pale yellow endosperm with a white crown. The plants derived from these seeds were crossed to plants which were homozygous recessive for the y1 and wc alleles (y1/y1, wc/wc). If A188 was homozygous for y1, the progeny kernels of this cross would be expected to segregate in a 1:2:1 ratio for pale yellow with white crown, white, and yellow endosperm. If, on the other hand, A188 was homozygous for Y1, the progeny kernels of this cross would be expected to segregate in a 1:1 ratio for yellow and pale yellow, white-crowned endosperm. The observed phenotypes and total number of kernels of each phenotype are found in Table 1. The chi-square values indicate that the data do not significantly deviate from a 1:2:1 ratio in six of seven crosses. In the seventh cross, the data deviated significantly at the 5% level. The total counts for all seven ears do not significantly deviate from 1:2:1. We conclude from these data that inbred line A188 is homozygous for the recessive y1 allele.

Table 1. Kernel counts for the testcross [A188 x Y1 Y1 wc wc] x y1 y1 wc wc.
 

	Endosperm Phenotype
Ear number	pale yellow- white crown	white	yellow	Chi-square value
4622-5/5696-6	49	103	54	0.242
4622-2/5724-3	74	106	57	5.076
4622-4/5696-6	61	127	53	1.232
4622-9/5696-6	59	121	60	0.016
4622-3/5622-1	31	56	37	1.742
4622-7/5696-6	17	53	20	2.794
4622-1/5724-3	48	80	64	8.000*
Totals	339	646	345	1.140

*Chi-square significant at p < 0.05.

To determine if the dominant white gene in A188 is allelic to Wc, A188 plants were crossed to plants homozygous for Wc and y1 (Wc/Wc, y1/y1; inbred K55, supplied by Dr. Earl Patterson). The progeny kernels from this cross had white endosperm, which is in support of our finding that A188 is homozygous for y1. (If A188 was homozygous for Y1, this cross would have produced kernels with pale yellow, white-crowned endosperm.) The plants derived from these seeds were reciprocally crossed to plants homozygous for the Y1 and wc alleles. If the dominant white gene of A188 is allelic to Wc all of the kernels produced in this cross are expected to have pale yellow, white-crowned endosperm. If, on the other hand, the dominant white gene of A188 is not allelic and is unlinked to Wc, this cross is expected to produce kernels segregating in a 3:1 ratio for pale yellow, white-crowned to yellow endosperm. We found that all kernels produced from this cross were pale yellow with a white crown, therefore, the dominant white gene of inbred A188 is allelic to Wc.

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