The cytology and genetics of mode of reproduction in a facultatively apomictic accession of buffelgrass (Cenchrus ciliaris (L.) Link.)

Typescript (photocopy).Twelve plants were chosen from the progeny of a newly-acquired African accession of buffelgrass (accession 409674) for use as parents in a cytological study to characterize mode of reproduction. Using a cleared-carpel technique and light microscopy, three of the plants were classified as obligately sexual, and nine of the plants were classified facultatively apomictic. Sexual megagametogenesis was of the polygonum-type in all parents, and the mechanism of apomixis in the facultatively apomictic parents was apospory and pseudogamy. Each of the facultatively apomictic parents produced ovules containing a single sexual megagametophyte, ovules containing both sexual and aposporic megagametophytes, and ovules containing only aposporic megagametophytes. The facultatively apomictic parents produced very few offtype progeny regardless of the male parent used. Abortion among the sexual megagametophytes of each parent caused by meiotic aberrations was suggested as the primary reason for the lack of sexual reproduction by the facultative apomicts. All self-progeny and hybrid progeny of the three obligately sexual parents were either obligately sexual or facultatively apomictic. A genetic study was conducted using the obligately sexual parents, and mode of reproduction in these plants was found to be genetically controlled. Because of the low fertility of the obligately sexual parents caused by meiotic aberrations, a strong influence of environment on segregation of mode of reproduction among the self-progeny, and inbreeding depression among the self-progeny, no specific models for the genetic control of mode of reproduction could be developed. For these same reasons, the obligately sexual parents have limited potential for use in a breeding program