Method of Reproduction in Napiergrass and in the 3X and 6X Alloploid Hybrids with Pearl Millet1

Abstract

Research on napiergrass, Pennisetum purpureum Schumach. (2n = 28), has been emphasized in the United States and in India, Africa, South America and other tropical and subtropical countries. Napiergrass has high yield potential and produces interspecific hybrids with pearl millet, P. americanum (L.) Leeke (2n = 14) that have both high yield potential and high forage quality. There are numerous reports on chromosomal behavior and number in napiergrass and in the pearl millet · napiergrass hybrids but there is only one limited report on embryo sac development in napiergrass and it appears to be inaccurate. The objective of this research was to establish the method of reproduction in napiergrass and in the triploid (3x = 21) and hexaploid (6x = 42) alloploids of crosses of napiergrass with pearl millet. Cytological observations showed that megasporogenesis and embryo sac development were typically sexual in 12 napiergrass accessions and four hexaploid interspecific hybrids. A large number (736) of interspecific hybrids were produced using six different napiergrass accessions as the female parent, which confirmed that napiergrass is a sexually reproducing species. The triploid interspecific hybrids also were sexual, but in over 99% of the ovules, all of the megaspores in the linear tetrad aborted resulting in an ovule without an embryo sac. Since the hexaploids were highly male and female fertile, they should be easy to use in a backcrossing program for the transfer of germplasm between species. The triploids have excellent forage potential but cannot be used in backcrossing because of their high male and female sterility.