We planted an F2 segregating line of ms*-6055 in our 1999 Johnston, IA, nursery to determine the chromosome arm map location of the mutant as part of our standard procedure in working with unmapped male-sterile mutants. We first determine the chromosome arm location. Then we conduct the appropriate allele test-crosses. Leaf punches were taken from 24 male-sterile plants and from 24 male-fertile plants for DNA isolation. 96 SSR markers, dispersed throughout the genome, were used to genotype these samples. Markers phi445613 and phi070, on chromosome 6, were linked to the mutation, with three recombinant alleles out of 20 mutant plants (40 alleles) and four recombinant alleles out of 22 mutant plants, respectively. This linkage indicates that ms*-6055 maps to the long arm of chromosome 6.
After receiving the mapping data, we test-crossed ms*-6055 with
the recessive male-sterile mutants found on chromosome 6 (ms1),
as well as the unmapped male-sterile mutants (ms27, ms31)
and those with questionable mapping data (ms35). We did not test-cross
this with the dominant male-sterile mutant, Ms42, nor could we test-cross
this with the lost male-sterile mutant, Ms21. The resultant progeny
were grown in our 2001 Johnston nursery. At least 40 plants were observed
for each test-cross. All test-cross progeny were found to be fertile, indicating
that ms*-6055 was not allelic to any of the tested mutants. Our
new designation for male-sterile mutant ms*-6055 is ms50.
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