Meiotic and Reproductive Behavior of Facultative Apomictic BC1 Offspring Derived from Pennisetum americanum‐P. orientale Interspecific Hybrids1

Abstract

This study reports on the chromosome numbers, meiotic behavior, method of reproduction and fertility of BC1 progenies from Penniserum americanum L. Leeke, pearl millet ✕ P. orientale L.C. Rich. interspecific hybrids backcrossed to P. americanum. This information would be useful for future studies on transfer of genes controlling apomixis from the tertiary gene pool to P. americanum. Two facultatively apomictic interspecific hybrids between Pennisetum americanum, (A. chromosomes) and P. orientale (O chromosomes), 2n = 25, were pollinated with P. americanum. Sixteen backcross progenies were obtainewhich were of three cytotypes: 32‐(14 A + 18 O), 23‐ (14 A + 9 O)and 27‐(7 A + 20 O) chromosomes. They resulted from fertilization of unreduced gametes or partially reduced gametes by a 7 A chromosome gamete, or by development or unreduced aposporic embryo sacs, respectively. In 23 chromosome plants, the 14 A chromosomes paired mainly as blvalents or remained as univalents while the 9 O chromosomes appeared as univalents, Intergenomal pairing between P. americanum and P. orientale also were observed and could make segmental exchange possible. In the 27 chromosome progeny, the 20 O chromosomes paired, while the 7 A chromosomes remained as univalents. Meiotic behavior in 32‐chromosome plants was regular with 7 A bivalents plus 9 O bivalents. The backcross progenies were male sterile but partially female fertile and produced a few seeds when pollinated with P. americanum pollen. The 23‐chromosome, BC1 progeny were reconstituted in BC2 progenies of 32‐ chromosome plants ✕ pearl millet. All BC1 progenies had some degree of apomictic embryo sac development and the 23‐chromosome plants showed apomictic development even though the O chromosomes on which the genes controlling apomixis are located were in the simplex condition. Both the 23‐and 32‐chromosome plants showed facultative apomictic development whereas the 27‐chromosome plants showed only obligate apomictic development, Intergenome pairing, chromosome instability, female fertility in 32‐chromosome plants, and the expression of apomixis genes in both the simplex and duplex condition indicates that genes controlling apomixis may be transferred from the tertiary gene pool to pearl millet using various gene transfer and recombination techniques.