Interval mapping a new dominant male-sterile mutant, Ms42
--M. C. Albertsen, T. W. Fox, M. R. Trimnell and M. G. Neuffer

One of the dominant male-sterile mutations that MGN identified from his EMS pollen mutagenesis research was designated Ms*-2082. This dominant male sterile exhibited extremely poor penetrance in both Mo17 and B73 as there was a shortage of male-sterile plants in crosses that should have segregated 1:1 for fertility vs. sterility. Previous experience with A632 suggested that male-sterile mutants often segregated more as expected in this background. We backcrossed Ms*-2082 into A632 and observed 1:1 segregation ratios after a few backcrosses.

Genetically mapping a dominant male sterile can be tedious. We decided to utilize RFLP interval mapping as a way to determine the chromosome arm location of Ms*-2082. Leaves were collected from 30 male-sterile plants and 30 male-fertile plants, and were bulked according to fertility. DNA was CTAB-extracted; digested with BamHI, EcoRI, and HindIII, and transferred to Duralon-UV. Membranes were probed sequentially with 23 probes from 17 of the 20 chromosome arms. Probe bnl6.25 (chromosome 5S) gave polymorphisms across all three enzymes, with Ms*-2082 exhibiting unique bands as well as bands in common with the bulked fertiles. Probe umc50 (chromosome 5S) also gave polymorphisms with EcoRI and HindIII. It showed a new band in the steriles, as well as bands in common with the fertiles. Although all chromosome arms are not yet covered, the differential probe hybridizations are strongly indicative that the gene is located on the short arm of chromosome 5.

We propose to designate Ms*-2082 as Ms42, as it now segregates as a single dominant gene and we have reasonable mapping information on it. Although Ms44 is currently the highest numbered male-sterile mutant, there are several gaps in the numbering of male-sterile mutations. We decided to fill in these gaps where we are certain that no previous designation exists. There are currently only two other dominant male sterile mutants in maize that are described and that have available seed stocks. These are Ms41 and Ms44. A third dominant male sterile, Ms21, has been lost. All existing dominant male-sterile mutations have been derived from EMS mutagenesis. Ms41 and Ms42 are from EMS pollen mutagenesis, and Ms44 is from EMS seed mutagenesis. 

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