Pollen Germination and Pollen Tube Growth of Sorghum when Crossed to Maize and Pearl Millet¹

Because of contradictory reports on the ability of sorghum [ Sorghum bicolor (L.) Moench] pollen to grow in alien gynoecia, sorghum pollen growth was studied on both maize ( Zea mays L.) and pearl millet [ Pennisetum americanum (L.) Leeke]. The study was made in several environments in order to determine the feasibility of hybrid production. Sorghum pollen germinated on and penetrated the stylar tissue in both maize and pearl millet. While the majority of pollen germination occurred on the stigma, germination was observed on all parts of the gynoecium: stigma, style, and ovary, in both genera. Pollen tubes behaved erratically in styles and usually were short. Individual pollen tubes of up to 15 mm long were observed in maize, and up to 6 mm long in pearl millet. In intact maize and pearl millet × sorghum crosses 0.1 to 0.2% of the gynoecia examined had pollen tubes in the ovary with less than half being observed at the micropyle. Such observations, even at low frequency, indicate that delivery of the sorghum male gamete is physically possible after regular pollination in both maize and pearl millet. However results were variable and work continues to assess the factors that affect pollen viability, pollen germination, and pollen tube growth