The Analysis of a Case of Cross-Sterility in Maize

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Abstract
A gametophyte factor designated Ga1s was found to be stronger in its effect than Ga1 on chromosome 4. On styles homozygous for Ga1s, ga1 pollen failed to function even in the absence of competing pollen, and on styles heterozygous for Ga1s, ga1 pollen gave a partial seed set. Results from various crosses indicated Ga1 and Ga1s were ailelic. Linkage studies gave recombination values of 25.8% for Ga1s and Su, compared to 27.8% for Ga1 and Su (on the basis of 4% functioning of ga1 pollen ). The discrepancy in these values was detd. by appropriate crosses to be due to the amount of functioning ga1 pollen. Ga1s pollen had a selective advantage in competition with Ga1 pollen on both Ga1 and Ga1s styles. Observations showed that ga1 pollen on Ga1s silks was able to germinate and penetrate the stylar tissue. It is suggested that the cross sterility may be due to failure of the pollen tubes to reach the ovule or to some abnormal reaction within the ovule. The action of Ga1s may account for a number of cases of cross-sterility in maize, particularly among popcorn varieties.
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