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Cytology and Reproduction of Reciprocal Backcrosses Between Pearl Millet and Sexual and Apomictic Hybrids of Pearl Millet x Pennisetum squamulatum¹

Interspecific hybrids (2n = 41) between pearl millet, Pennisetum americanum L. Leeke (2n = 4x = 28), and P. squamulatum Fresen (2n = 6x = 54) were used ~s pollen and maternal parents and backcrossed (BC) to pearl mi}let to determine the potential for germplasm exchange and for transfer of apomixis to pearl millet. Backcrosses to diploid pearl millet (2n = 14) resulted in 12 28- or 27-chromosome male and female-sterile plants from more than 600 pollinated inttorescences. Backcrosses to tetraploid pearl millet (2n = 4x = 28) resulted in 2830 BC₁ progenies (crossability 91%). These BC₁ progenies had somatic chromosome numbers ranging from 2n = 32 to 2n = 39 with a mode of 2n = 35 chromosomes. They were perennial and more closely resembled pearl millet in morphological characteristics than did the original interspecific hybrids. Meiosis was irregular with a mean of 4.88 bivalents. Univalents, trivalents, quadrivalents, and other multivalents were present in all microsporocytes. Eightyfour percent of these plants did not shed pollen and the remaining 16% were semi-sterile with pollen stainability ranging up to 6.6%. Among 177 semi-sterile BC₁ plants resulting from crosses with highly apomictic F₁ hybrids as pollen parents, 55 progenies showed only apomictic t:mbryo sac development. Seed set ranged from 0 to 14 seed per head under open-pollination. Similar chromosome behavior and fertility as above were observed in progeny from reciprocal backcrosses between the sexual interspecific hybrids and diploid or tetraploid pearl millet. The production of partially male-fertile apomictic BC₁ plants should make it possible to continete gene transfer from P. squamulatum to pearl millet in succeeding generations.

Key Words: Germplasm • Chromosome • Embryo sac • Gene • Tertiary gene pool • Gene transfer

² Cooperative research associate and research geneticist, USDA-ARS, and the Univ. of Georgia, College of Agric. Exp. Stns., Coastal Plain Exp. Stn., Agronomy Dep., Tifton, GA 31793.

Received for publication April 2, 1984.