CYTOTAXONOMY AND EVOLUTIONARY SIGNIFICANCE OF 2 OFFTYPE MILLET PLANTS - DERIVED FROM A PEARL-MILLET X (PEARL-MILLET X PENNISETUM SQUAMULATUM) APOMICTIC HYBRID

Twenty-six pearl millet, Pennisetum americanum L. Leeke .times. (P. americanum .times. Pennisetum squamulatum Fresen) obligate apomictic hybrids were progeny tested and two offtypes were found among the progeny consisting of 780 individuals. The two plants differed morphologically from the maternal and other offspring, and had 2n = 56 chromosomes. Both likely resulted from the fertilization of an unreduced egg from the apomictic BC1 hybrid (2n = 35) by a 21-chromosome gamete possibly produced by a hexaploid interspecific hybrid (2n = 42) involving Pennisetum purpureum Schumach. At metaphase I, chromosomes remained as univalents (.hivin.x = 10.50) paired as bivalents (.hivin.x = 11.97) or associated in multivalents. Both offtypes were partially male fertile with 37 percent and 47 percent of pollen stainability, respectively. Offtype I was obligately apomictic with 98 percent of aposporous embryo sacs, but completely female sterile. Offtype 2 was a facultative apomict with 16 percent and 73 percent of ovules with eight-and four-nucleate mature embryo sacs respectively. Offtype 2 set a mean of 5 open-pollinated seed per head. Eight progeny from offtype 2 each had 2n = 56 chromosomes. Results showed the role of apomixis in producing and maintaining plants with new genome combinations and at a new ploidy level. Apomixis made possible the production and maintenance of the pearl millet A genome at the pentaploid level. Facultative apomixis and partial male and female fertility in one of the 56-chromosome plants allowed for the maintenance of a new cytotype as well as for production of new 56-chromosome genotypes and new cytotypes.