Inheritance and Control of Obligate Apomixis in Breeding Buffelgrass, Pennisetum ciliare1

Abstract

We studied the inheritance of obligate apomixis, using both selfed and F1 progenies. In both cases, the female parent was a completely sexual plant heterozygous for genes controlling method of reproduction, and the male parents in the crosses were obligate apomicts. Classification of S1 and F1 plants for mode of reproduction was achieved by embryo‐sac analyses, or study of progeny variability, or both. Four hundred and sixty‐nine S1 progeny, involving two populations grown in the years 1962 and 1965, respectively, segregated for sexual to apomictic types at ratios not significantly different from a 13:3. One hundred and forty‐five S1 progeny grown in 1963 gave a sexual to apomictic ratio of 8.66:l. Pooled data for these 614 S1 progeny of the sexual plant fit the 13:3 ratio. Seven hundred and sixty‐six F1 hybrids between the sexual plant and two obligate apomictic ecotypes, blue and common, gave sexual to apomictic ratios not significantly different from a 5:3. Interpretation of the 13:3 S1 and 5:3 F1 sexual to apomictic ratios is as follows. The genetic constitution of the sexual plant is hypothesized to be AaBb, where gene B conditions sexuality, and it is epistatic to gene A, which controls apomixis. The genetic constitution of the apomictic male parents is hypothesized to be Aabb. Results obtained support the hypothesis and suggest that the sexual plant originated by mutation at the b locus. The manipulation and use of obligate apomixis in a buffelgrass breeding program is discussed.