Further tests of the derived A188 and the T6-9b sources show that neither is a cytoplasmic restorer of genetic ms1. Crosses made to test the cytoplasm of diploperennis will be grown in 1983.
I am now using the following method for testing. Step 1: The stock to be tested is crossed as the female parent with a known ms heterozygote. Step 2: The resulting F1 plants (5 to 10 plants) are crossed as female parents with the ms heterozygote and also crossed as the pollen parent on ms plants as females. If the stock being tested has the cytoplasmic restorer, none of the progeny in step 2 from the cross of the stock as female with ms heterozygotes will segregate male sterility. To be certain of the results, these progeny can be crossed again with ms heterozygotes. If there is no segregation for male sterility, many of the fertilized plants will be [R] ms ms. These are identified by the crosses on ms plants.
Chas. R. Burnham
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