I had assumed that if the homozygote for the inactivated normal allele of a male sterile gene could be established, it could be used as an alternative method of producing "all male sterile progeny" for use in producing hybrid corn (MGNL 50: 82; MGNL 51:54). Although the progeny of male steriles crossed with homozygous inactivated (Ims/Ims) pollen should all be male sterile, the male steriles used for the crosses would occur in segregating cultures. Hence, as pointed out by Phillips and Albertsen (personal communication), this is not an efficient alternative method, since a system for the mass production of ms/Ims progeny (male sterile) would be difficult to develop.
Although the inactivated locus is transmitted through pollen and ovules for two lines for ms and two for ms2, tests in 1977 and earlier years, of the self progeny of heterozygotes (Ims/+), have not identified a single homozygote (Ims/Ims). Tests are in progress using linked genetic markers as an aid in selecting putative homozygotes. For ms, y and pb are being used, and for ms2, ar wx is being used. The crosses were selfed by A. S. Wang in Hawaii and the progeny were grown in 1977.
For ms, 13 cultures segregated male sterility and 15 did not. The latter should be from heterozygous Ims plants. From 6 of them which also had Y y as the marker, 72 plants were segregating Y y and one was Y Y. This Y Y plant is a putative homozygote for the inactivated locus and will be tested
For ms2, 69 cultures segregated male sterility. The 29 which did not should be from heterozygous (Ims/+) plants. From the latter, 397 plants were segregating for waxy, 46 were Wx Wx (11.8% of the total). Although most of the latter are probably not homozygotes for Ims, since wx and ms2 are 8 units apart on the linkage map, the marker still greatly reduces the number of plants to be tested.
Hopefully if the homozygotes can be established, someone may find a use for them.
Charles R. Burnham
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