Because yellow vs. white pollen color is determined by the genotype of the sporophyte (presumably of the anther wall), the effect of mutable c2 alleles with whp should be to confer yellow pigmentation on pollen grains within the pollen sac adjacent to C2 wall tissue, resulting in mixed white and yellow pollen. Combinations were derived involving whp with c2-m1 (autonomous, Spm-controlled) and c2-m2 (two-element, Spm-controlled).

Plants homozygous for whp and heterozygous for c2-m1/c2 have been derived; they produce uniformly yellow pollen grains. Anthers on such plants, if they are R-r Pl, show well-defined sectors that include sizable tracts of colorless tissue. For c2-m1, the expectation of mixed white and yellow pollen was not found.

Four plants homozygous for whp and heterozygous for c2-m2/c2 with C1/c1-m5.Spm have been derived; each produced mixed white and yellow pollen. Three plants were R-r Pl Bz, in which purple sectors in the anthers were well-defined. The fourth plant was bz bz, and displayed yellow-fluorescent sectors in the anther walls. Presumably c2-m2 is itself null in function until mutations to C2 occur, while c2-m1 is itself functional at a level sufficient to confer yellow pollen color.

Color (ammonia-enhanced yellow) in pollen samples from individual c2-m2 anthers with large purple sectors showed a general relationship to the size of the sector. Among 6 anthers with 75-100% purple walls, 3 contained mostly or entirely yellow pollen, 2 contained mixed yellow and light yellow or white, and 1 contained white pollen. Among 11 anthers with 30-50% purple walls, 2 contained mostly or entirely yellow pollen, 3 contained mixed yellow or light yellow and white, 2 contained light yellow, and 4 contained white pollen. These observations can be related to the tests performed by Rhoades (Genetics 23:377, 1938) with Dt-induced sectors in anthers, in which a relationship was found between sector size in the anther wall and the percentage of A progeny from that anther. Unfortunately the few single-anther pollinations attempted with the c2-m2 material were unsuccessful. A single bulk pollination from one of the three plants with purple-sectored anthers and mixed yellow and white pollen, in a testcross on c2, gave half mutable and half colorless kernels (i.e., there were no progeny from the C2 sectors that were assumed to be present). The expected ratio is 1/4 mutable and 3/4 colorless. Why the testcross ratio might be 1:1 is unclear.

E. H. Coe, Jr.

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