New chromosome 3S mutant mssi*-DR87A --Trimnell, MR, Fox, TW, Wilkinson, D, Albertsen, MC In 1987, Dan Wilkinson observed male-sterile plants in a Uq c-ruq/Ht1 F2 line that he was growing in Johnston, IA. Dan sib-pollinated the male-sterile plants and gave the seed to us. We planted this seed in our 1988 Johnston summer nursery where the male-sterile plants were again sib-pollinated. We designated this male-sterile as ms*-DR87A. Segregation data for the 1988 nursery are shown:
 
Genotype Fertiles Steriles X2(1:1)
Uq Sib #1 12 Fertiles 12 Steriles 0.00
Uq Sib #2 13 Fertiles  18 Steriles 0.81
Uq Sib #3 10 Fertiles 10 Steriles 0.00
Original F2 Line 13 Fertiles 4 Steriles 0.01 (corrected X2)(3:1)

In 1992 we test-crossed ms*-DR87A with a Uq tester line (receptor @ c1;c-ruq wx). We scored the ears from this test-cross for Uq co-segregation with sterility but did not find consistant co-segregation. While scoring these ears we noticed that there was an unusual number of silks on the male-sterile plants, as well as glume-like structures attached on either side of the kernels. Sometimes these structures are separated from the kernels during the shelling process (using a mechanical sheller), but most of the time they remain joined to the kernel on either side.

During the summer of 1995 in Johnston, we grew the sib-pollinated seed from the 1988 nursery. At that time, male-sterile plants were crossed with A632. The F1 seed was grown in the summer of 1995 and self-pollinated to make F2 ears. The F2 ears were then planted in the 1995 Hawaii winter nursery; their segregation data are shown:
 
Genotype Fertiles Steriles Corrected X2(3:1)
A632 Ear #1 10 Fertiles 7 Steriles 1.59 
A632 Ear #2 11 Fertiles  6 Steriles 0.50

In the Hawaii 1997 winter nursery, ms*-DR87A was planted for chromosome arm mapping. Leaf punches from 24 male-fertile and 15 male-sterile plants were taken for DNA isolations. Roughly 60 SSR markers were used to genotype DNA pools of the male-fertile samples and individual male-sterile samples. Four SSR markers on chromosome 3 (bnlg1035, bnlg1452, phi029, phi053) showed linkage with the male-sterility phenotype. SSR marker bnlg1035 (chromosome 3 Bin 5) gave the closest linkage to the trait with only 2 recombinant alleles found in the male-sterile samples.

Test-crosses were made with ms*-DR87A and the known male-sterile mutants located on chromosome 3 (ms3, ms23, ms37) as well as with the unmapped male-sterile mutants (ms24 and ms27). At least 40 plants were observed for each test-cross, and all test-cross progeny were found to be fertile. We also had test-crossed ms*-DR87A with si1 before we had map data and found that it was not allelic. The si1 mutant is described as having irregular kernel placement, but there is no description of glume-like structures attached to the kernel. The ms-si*-355 allele listed in the back of last year’s MGN is without description.

Other than the si1-mssi allele, none of the other si-type mutants identified by Neuffer are described specifically as also being male sterile. This includes si*-1323 (or si*-N1323) that is mapped to chromosome 3S and that is described as "a selfed colorless flinty semi-sterile ear segregating for tiny defective kernels with excess silks" (MaizeDB). Its male fertility is not addressed. Silky mutant si*-1967(or si*-N1967) is not mapped but is described as being male fertile (MaizeDB). Silky mutant si*-N815A, also unmapped, is described as having silks on tassels and ears (MaizeDB).

None of the previously described silky-type mutants have all the features of ms*-DR87A. Homozygous mutant plants are 1) distinctly male sterile, 2) have glume-like structures attached on either side of the kernel, and 3) have excess silks on the ears. Because of the silky phenotype of this male-sterile, our designation for this mapped mutant is mssi*-DR87A.
 
 


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