Apomixis in sorghum : mode of reproduction, inheritance, and improvement of apomictic frequency

Vita.Five selected sorghum (Sorghum bicolor (L.) Moench) lines, R473, Polygynaceous line (PGY), White seed mutant (WS), South Dakota line (Experimental 3-58) (SD), and Double haploid of 'Tx403' (DH) were studied for mode of reproduction, inheritance of apomixis, and the effects of sexual suppressants on apomictic frequency. This information was used to assess the potential for use of apomixis in sorghum breeding. Two approaches were used for detecting apomixis, namely, embryo sac analyses (paraffin section method and ovule squash method), and progeny evaluation (test crosses and progeny tests). Advantages and disadvantages of these techniques were discussed. Choice of the technique depends on the materials available and the objectives of the study. Apomixis was observed in the five sorghum lines studied. Sexual reproduction was found along with apomixis in each line. Nucellar activity occurred at various stages of embryo sac development. The mechanism of apomixis in sorghum was a type of facultative apospory. R473 had the highest apomictic frequency (22.8%) as determined by embryo sac analyses. Degeneration of the embryo sac mother cells was noticed in some ovules at the early stages of development. R473 was incompatible; thus no test crosses were obtained. Use of apomixis from this line depends on the success of isolating apomictic lines which are not incompatible.