Mapping effort for locating whp continued. The arm segments remaining (Modena, MNL 56:48) were tested. Candidate hypoploid plants were identified by distinctive morphology and at least 50% pollen abortion for 1S, 2S, and 10L. All shed yellow pollen. The test using TB-10Sc yielded all normal looking plants, but six out of sixty-two were semi-sterile and all shed yellow pollen. Therefore, the above arms are eliminated.

Randomization was indicated in linkage tests with the following markers: Vg, c2, pro, and wx. The 1-centromeric, 4L, 8-centromeric and 8S(?), and 9-centromeric regions are eliminated. A test with Lg3 confirms elimination of the 3-centromeric region.

Another test with a marked 2S chromosome yielded white pollen plants in coordination with multiple, distal homozygosities, confirming elimination of distal 2S. Unpublished data indicate that B and whp randomize, which eliminates the proximal 2S and 2-centromeric region.

Another test with a marked 2S chromosome yielded white pollen plants in coordination with multiple, distal homozygosities, confirming elimination of distal 2S. Unpublished data indicate that B and whp randomize, which eliminates the proximal 2S and 2-centromeric region.

A test with TB-3La-2L7285 appears to have uncovered whp, placing it on 2L. Among 54 plants observed, 16 plants were candidate hypoploids based on both morphology and pollen abortion percentage. Twelve shed white pollen and four shed yellow pollen. Additionally, two plants of normal stature with no pollen abortion, whatsoever, also shed white pollen. In the early stages of convertinq the TB stocks to c2/c2, they were all crossed to a c2 source that had partial K55 lineage. This was before K55 was recognized as the source of the whp allele. Effort will be directed to specific linkage tests on 2L.

But there is more! TB-9Sb-4L6222-generated hypoploids also shed white pollen. The putative hypoploids were semi-sterile and less than two feet tall. Thirteen yielded white pollen and five, yellow pollen. Four different TB pollen parents were involved: 3 yp:2 wp; 2 yp:4 wp; 0 yp:1 wp; 0 yp:6 wp. These have had contact with K55 in their derivation. All available TB arms have been tested and only these two arms have tested positively for white pollen phenotype. whp is not close to su or the TB-4Sa breakpoint (Modena, MNL 56:48). Linkage tests this past summer clearly demonstrated that c2 and whp are randomizing. If whp is distal to c2 on 4L, then it becomes impossible for hypoploid c2, whp plants to ever shed yellow pollen! A non-compound TB for 4L of different origin has been crossed to white pollen plants to clear this point up.

Stephen A. Modena

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