Tests to identify plants that are ms1 ms1 but fertile because of an [R] cytoplasm that restores fertility were continued with the line derived from T6-9b. Plants shown to be Ms1 ms1 by test-crosses on ms1 ms1 produced self progenies that had no male sterile progeny. Plants in those progenies were selfed and test-crossed on ms1 ms1 plants, of the 61 plants tested 42 were shown to be Ms Ms and 19 were Ms ms. None were ms1 ms1 but fertile. Progeny from selfs of the Ms ms plants were grown only in small numbers. Larger numbers will be grown in 1986. These should have no male sterile plants if the line being tested has the restorer cytoplasm.

For testing additional stocks for a cytoplasm that restores fertility to a genetic male sterile, an interchange stock (T) with one breakpoint closely linked to the male sterile may be used. The stock to be tested is then crossed with pollen from T/ms. Except for crossovers between ms and the T breakpoint, the fertile progeny will be Ms ms. If these fertile plants are again crossed as female with T/ms, half the fertile progeny should be ms ms. This will provide a test of the ability of the stock to restore fertility. It will also increase the efficiency of identifying plants that are [R] ms ms. The first step was used to a limited extent in this study, but the usefulness of the second step was not realized until late this summer.

Chas. Burnham
 
 

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