Two selections of Minn A632 in Pr-cytoplasm, A632-Pr-rf, a male fertile selection, and A632-Pr-ms, a male sterile selection, were grown under two temperature treatments. The day length was set at 14 hours and the day temperature at 29 C in both treatments. The night temperature was 18 C in one treatment and 10 C in the other. Two replications were done per treatment.
When grown under warm night temperatures, 16 of 16 A632-Pr-rf plants were fertile, while 15 of 16 plants of the same genotype were fertile under cooler nights (Table 3). No differences in the degree of male fertility were observed between the two treatments. Differences were observed, however, when A632-Pr-ms plants were grown under the two different treatments. Under warm nights only 1 of 16 plants was fertile, however 13 of 16 were fertile under cool nights (Table 3). Those A632 Pr-ms plants which were fertile exserted only 1% of their anthers, under either treatment. They were far less male fertile than the A632 Pr-rf plants, which exserted 75 to 100% of their anthers.
The differences due to temperature and genotypes were found to be highly significant. The genotype by temperature interaction was also highly significant (Table 4).
While it is clear that different night temperature affected the expression of male sterility induced by Pr-cytoplasm Minn A632, it is unclear which parameter does so. The change from male sterility to weak fertility might be induced by the night temperature, the mean temperature, or the day-night temperature difference. However, due to the generation time of Minn A632, identifying the major factor would require a number of growth chambers over a number of years.
W. F. Tracy, H. L. Everett and V. E. Gracen
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