We planted an F2 segregating line of
ms*-6036 in our 1998 Hawaii nursery to determine the chromosome
arm map location of the mutant as part of our standard procedure in working
with previously unlocated male steriles. We first determine the chromosome
arm location, then we conduct the appropriate allelism crosses. Leaf punches
were taken from 24 male-sterile plants and from 24 male-fertile plants
for DNA isolation. SSR markers were used to genotype these samples. Out
of 72 randomly dispersed SSR markers, only one, phi034, showed linkage
to the male sterility trait. This marker maps to bin 7.02 on chromosome
7, and segregates with ms*-6036 as follows:
| Homozygous (A) | Heterozygous (AC) | Homozygous (C) | Failed Rxn�s | |
| Fertile |
|
|
|
|
| Sterile |
|
|
|
|
Although only one marker showed linkage,
we proceeded to test-cross ms*-6036 with the recessive male-sterile
mutants that are located on chromosome 7 (ms7, ms22, ms34),
as well as with an unmapped recessive male-sterile mutant (ms27).
The resultant progeny were grown in our 2000 Johnston, Iowa, nursery. At
least 40 plants were observed for each of the test-crosses. The reciprocal
test-crosses with ms27, ms7 and ms34 produced all
fertile progeny, indicating ms*-6036 was not allelic to them. The
reciprocal test-crosses of ms*-6036 with ms22 gave the following
results, indicating allelism:
| Female | Male |
|
X2 | |
| ms*-6036 Heterozygote | ms22 Het |
|
|
0.79 (3:1) |
| ms22 Homozygote | ms*-6036 Het |
|
|
0.33 (1:1) |
Our new designation for this Ms22
male-sterile allele is ms22-6036.
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