We received remnant seed from an EMS seed-mutagenized W23 plant in 1978 from Dr. R.L. Phillips at the University of Minnesota. This seed was brought to my attention because plants had exhibited male sterility segregation, even after being crossed by normal W23. Subsequent crosses established that the male sterility was the result of a dominant, nuclear mutation at a previously undescribed locus. In 1983 sufficient data had been collected on this mutant to locate it to chromosome arm 4L using the waxy translocation series. We did not publish these results because we had wanted to complete an on-going developmental study of the microsporogenesis of this mutant and to present it with the genetic segregation data. In 1987, Dr. M.G. Neuffer from the University of Missouri presented mapping information on a dominant male sterile he had isolated from his EMS pollen mutagenesis work. He gave this dominant male sterile the designation Ms41 and located it on 4L using the waxy translocation series. When we compared his data to our data, we discovered that our dominant male sterile, which we had designated Ms*-7255, seemed to map very similarly to his Ms41.
These data show independence chi-square values that are highly significant for T4-9b and T4-9g. The value is extremely high for T4-9b, indicating a strong departure from independence and, therefore, indicating linkage. The value for T4-9g is not nearly as high. We do not know whether this represents reality or not because the breakpoint for T4-9g is across the centromere from Ms*-7255 on the short arm of chromosome 4. There are 2 other interchanges that show significance. Although the significant values could indicate factors that impact expression of Ms*-7255 are on these chromosomes, the barely significant values more likely represent problems in sterility classification. Much of the background of this mutant is W23. This inbred has the tendency for fertile plants to appear sterile in certain environments. Unfortunately, it was not possible to use the same source of Ms*-7255 for each cross with the waxy translocation series. Some of the sources were better than others for stable expression of the male-sterile phenotype. We have repeated some of these crosses. Results will be available in 1988.
We do not know whether Ms41 and Ms*-7255 represent the same locus or not. Because Ms41 can shed pollen in some environments, we may be able to make testcrosses with Ms*-7255. If this fails, we will rely either on RFLP's or conventional mapping to determine allelism of these 2 dominant male steriles. It is of interest to note that both of these dominant male steriles apparently resulted from EMS mutagenesis. In one case the EMS treatment was on kernels, and in the other, it was on pollen.
M.C. Albertsen and L.M. Sellner
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