Incidence of downy mildew on pearl millet male-sterile lines at Jodhpur, Rajasthan, India

摘要

Since the release of the first series of pearl millet [Pennisetum glaucum (L.) R. Br.] hybrids in India during the late 1960s, downy mildew (DM) [Sclerospora graminicola (Sacc.) J. Schrot] has assumed national standing as a disease of significant economic importance. During the last 3 decades, considerable efforts have been made to manage this disease. The recurrence of DM in 1995, after a gap of 7 years indicated the limitations of exploiting single-cross F_1 hybrids. Single-cross hybrids are genetically uniform, and become susceptible to DM within 3-5 years of their release because strains of the pathogen, specifically adapted to the new hybrid multiply rapidly (Thakur et al. 1999). To successfully cultivate a hybrid for a longer period in a given area it is imperative that the hybrid and both its parents posses resistance to the DM pathotypes existing in that region; failing which it would be risky to introduce a hybrid. To check the rapid multiplication and spread of a virulent pathotype, itis essential to broaden the genetic base of hybrids already in cultivation. This led to efforts to diversify the genetic base of male-sterile (ms) lines by transferring A_1 cytoplasm to other genetic backgrounds, and to develop new ms lines based on different sources of male-sterility-inducing cytoplasm. However, the majority of available pearl millet ms lines are still based on A_1 cytoplasm, because it is easier to obtain restorers for A_1 cytoplasm than from other sources of stable pearl millet cytoplasmic male-sterility.