Inducing Male Fertility in Crosses Between Pearl Millet and Pennisetum orientale Rich

Male sterility in interspecific crosses between cultivated and wild species often interferes with the transfer of exotic germplasm. Our research objective was to investigate various pathways of inducing male fertility in interspecific hybrids of pearl millet (Pennisetum americanum L. Leeke) (2n = 14) ✕ Pennisetum orientale Rich. (2n = 36) and their derivatives. The F₁ interspecific hybrids between pearl millet (A chromosomes) and P. orientate (O chromosomes), 2n = 25 (7A + 18O), were partially female fertile and male sterile regardless of whether they received male-sterility-inducing or male-fertility-inducing cytoplasm from pearl millet. The BC₁ F₁ hybrids from backcrosses to diploid pearl millet as males included 23-chromosome (14A + 9O) and 27-chromosome (7A + 20O) derivatives that were male and female sterile, and 32-chromosome (14A + 18O) plants were partially female and male fertile, provided they received fertility-inducing cytoplasm. Male-fertile 32-chromosome plants also were produced by pollinating male-fertile tetraploid 2n = 4x = 28 pearl millet with P. orientate pollen. The 32-chromosome plants ranged in pollen stainability from 30 to 50%, were highly self-incompatible with only sparse, selfed seed set, and showed 2 to 4% aposporous embryo sac development. Tetraploid pearl millet ✕ 32-chromosome plant crosses produced BC derivatives, with 28 to 30 chromosomes but were male and female sterile. Crosses of 23-chromosome (14A + 9O) derivatives ✕ pearl millet produced 14-chromosome pearl millet progeny by elimination of the P. orientate genome. The 14-chromosome progeny lacked P. orientate characteristics. Because they are partially fertile, the 2n = 32 chromosome plants provided a valuable bridge for germplasm transfer between pearl millet and P. orientate. Germplasm transfer between genomes of the two species probably will require nonconventional methods such as use of radiation to produce small translocations or other genetic engineering methods such as vectors and transposable elements.