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Pearl Millet and Sorghum Pollen Tube Growth in Pearl Millet Gynoecia of Different Ages¹

The primary barrier to hybridization of pearl millet [Pennisetum americanum (L.) Leeke] with sorghum [Sorghum bicolor (L.) Moench] is arrest of pollen tube growth within the gynoecium. However, pollen tube growth in this cross is variable. This paper reports the effect of gynoecium age of pearl millet on pearl millet and sorghum pollen tube growth. Pearl millet stigmas were receptive to pollen immediately upon emergence and remained receptive to pollen germination and pollen tube penetration until abscission. Pearl millet pollen tubes grew normally in gynoecia having stigmas emerged for less than 4 days (younger gynoecia) at pollination, and fertilization occurred. Pollination of stigmas emerged for more than 4 days (older gynoecia) resulted in inhibition of pollen tube growth within the gynoecium. In contrast, sorghum pollen tube growth increased significantly in older vs. younger gynoecia. Sorghum pollen tubes in the ovary increased from 4% in younger to 22% in older gynoecia. Apparently the internal environment of pearl millet gynoecia changes with age. These changes appear to alter the pollen tube transmitting tract in the gynoecium making it inhibitory to pearl millet pollen tubes and less inhibitory to sorghum pollen tubes.

Key Words: Pennisetum americanum (L.) Leeke • Pennisetum typhoides (Burn.) Staph et Hubb • Pennisetum glaucum R. Br. • Sorghum bicolor (L.) Moench • Prefertilization barrier • Pollen tube growth • Gynoecium age • Intergenetic hybridization

² Plant physiologist, USDA/ARS, Russell Res. Ctr., Athens, GA 30613; and plant breeder, Centro Int. de Mejoramiento de Maiz y Trigo (CIMMYT), Londres 40, Mexico 6, D.F.

Received for publication August 18, 1982.