Genetic characterization and floral development of female sterile and stubby head, two aposporous mutants of pearl millet

 Apomixis has never been reported in natural populations of pearl millet Pennisetum glaucum (L.) R.Br.], although many wild relatives of pearl millet are obligate or facultative aposporous apomicts. Four-nucleate aposporous embryo sacs are formed from somatic cells of the nucellus that do not undergo meiosis. Two mutants of pearl millet, female sterile (fs) and stubby head, have two developmental characteristics in common: a significant reduction in head length compared with the wild-type and the formation of aposporous embryo sacs. Reproductive development in fs and stubby head mutants was examined in depth because of the potential for illuminating basic cellular or developmental factors that may function to alter embryo sac development. Genetic analysis of stubby head showed that this phenotype is conferred by genes at two loci linked in coupling within 29 cM. Crosses between fs and stubby head mutants showed that, despite the similarities in phenotypes, the mutations are at different loci. The mutants differ from wild-type in their inflorescence structure from the time of initiation of spikelet primordia through terminal differentiation of the ovule. Both mutations could be categorized as meristic, since a change in inflorescence branch or organ number was common and gynoecium development varied. We speculate that heterochronic development of the floral meristem and organ initiation/specification programs may be the underlying mechanism for phenotypic changes in these mutants throughout the floral phase. Received: 25 October 1996 / Accepted: 13 March 1997