Meiotic and Population Dynamics in the Indigenous Representatives of the A-genome Complex of the Genus Oryza Linn.

The savanna agroecology of Nigeria was surveyed for the occurrence of wild rice-three species of the A-genome complex (O. barthii, O. glaberrima and O. longistaminata) were found to be endemic. A total of 32 accessions of these species, including O. sativa were studied in situ and ex situ. Chromosome studies revealed regular pairing as 12II in the accessions per se. The O. glaberrimaxO. sativa crosses showed a preponderance of bivalent pairing as 12II, other associations like 24I, 10II + 1IV, precocious movement at Metaphase I and occurrence of two pairs of satellited chromosomes. The crosses were infertile. The O. glaberrimaxO. barthii cross was highly pollen and spikelet-fertile. A modal chromosome association of 12II was recorded. A translocation was seen at pachynema. The O. barthiixO. sativa cross was sterile with only a few shriveled seeds. The chromosomes showed many associations at diakinesis and budding of microspores was experienced during pollen mitosis. Some fertility was restored in the BC1 generation of the O. glaberrimaxO. sativa crosses; more fertility was restored in the BC1 F2. Fertility was not restored in the BC1F2 of the backcrosses involving O. glaberrima. Various meiotic disturbances were monitored in the backcross generations. Rice farming in the savanna agroecology of Nigeria (particularly in Jebba) is a peasant affair in small holdings circumscribed by wild rice. This creates an opportunity for natural hybridization. The population dynamics and phylogeny of the A-genome complex are enunciated based on this fact and the results of the cytogenetic studies carried out.