New chromosome 4 male-sterile mutant: ms52

New chromosome 4 male-sterile mutant: ms52

--Trimnell, MR, Fox, TW, Albertsen, MC

During the 1991 Hawaii winter nursery season, George Peverly pointed out to MCA some male-sterile plants segregating in a backcrossing line. We planted remnant seed of this line in our 1992 Johnston, IA, nursery and designated it ms*-PM91A. The planted rows segregated for the male-sterile phenotype, and male-sterile plants were crossed with A632 and B73. These F1 ears were self-pollinated and then grown in our 1994 Johnston nursery. We planted several selfed ears in our nursery, and they segregated as follows:

Genotype	# Fertile Plts	# Sterile Plts	χ²(3:1, P>0.050=3.84)
ms-PM91A*/A632)1	13	3	0.33
ms-PM91A*/A632)2	13	4	0.02
ms-PM91A*/B73)1	17	2	2.12
ms-PM91A*/B73)2	18	6	0.00

In the 2000 Johnston, IA, nursery, we planted an F2 segregating family to determine the chromosome arm map location of the mutant as part of our standard procedure in working with previously unmapped male-sterile mutants. First, we determine the chromosome arm location, and then we conduct the appropriate allele testcrosses. Leaf punches were taken from 24 male-sterile plants and from 24 male-fertile plants for DNA isolation. Ninety-six SSR markers were used to genotype these samples. Shown below are four chromosome 4 markers that show linkage to the mutation.

Marker	Recomb. Alleles	Mutant Plts	% Recombination (based on mutant segregants)
bnlg1265	1	22	2.2
bnlg1755	2	19	5.3
bnlg1189	6	18	16.7
phi438301	10	24	20.8

The ms*-PM91A mutation is close to the centromere, and it appears to be on the short arm of chromosome 4.

After receiving the mapping data, we testcrossed ms*-PM91A with the mapped recessive male-sterile mutants found on chromosome 4 (ms30), as well as the unmapped male-sterile mutants (ms27, ms31). The resultant progeny were grown in our 2002 Johnston, IA, nursery. At least 40 plants were observed for each testcross; all testcross progeny were found to be fertile, indicating that ms*-PM91A was not allelic to ms27, ms30, or ms31. Our new designation for male-sterile mutant ms*-PM91A is ms52-PM91A.