| An unrecognized sources of inoculum of wheat stern
rust in india Srikant KULKARNI Department of Plant Pathology University of Ariicultural Sciences Dharwad-500 005 (Karnataka State) India. Wheat in India is generally cultivated as a winter crop. In the Plains and South Indian plateau normally sown in late October or November and harvested in March or April. In South India, the crop matures by February end or early March but in the Northern Plains maturity is between last week of March to middle of April. Sometimes the late sown crops are delayed by a week or two. In Nilgiri and Pulney hills of South India two wheat crops are taken. The winter crop is sown in June and harvested in September. In the northern hills sowing is done a bit earlier than in the plains and crop normally matures by May except at high attitudes (7,000-8,000 ft a.s.l) where it matures by June. MEHTA (1952) had regarded Central Nepal and Niligri as "the most dangerous foci of infection". He had identified Nilgiri and Pulney hills as foci of infection of black and brown rusts from South India, and also recorded early appearance of black rust in place like Dharwad in the South. Till recently, it was thought that the primary inoculum of black rust is introduced in the plains from north as well as south. But according to JOSHI et al (1971) early appearance of black rust has been recorded in south or Central India in the month of January and February or at times even in December. It was observed in 1976-77, the stem rust incidence was less in Niligiri and Pulney hills but more in plains of Karnataka. Further more, the incidence of infection was too low throughout southern hills to produce the amount of inoculum required for observed infection. The race distribution determined from collection in Karnataka differed from that found in Southern hills. Hence, an extensive survey was conducted in Karnataka to locate the focus of infection of stem rust of wheat. The off season survey was conducted during 1980, 1981, and 1982 in Karnataka. It was found that, the farmers grow wheat during off season in the plains of Chikmagalur and Chitradurga districts of Karnataka. They sow right from May to September. This off season wheat is found in patches along with Onion and Coriander. It was found that, there was heavy stem rust infection on off season wheat. The races identified were 21 and 117A-1 of stem rust. The winter sowing starts from October onwards. Hence, there is a link between off season and normal season crop. The observations suggested a previously unrecognized source of wheat stem rust inoculum in India. Further field survey will investigate the potential of this area as a source wheat stem rust inoculum. References JOSHI, L.M., E.E. SAARI, & S.D. GERA, 1971. Epidemiological aspect of Puccinia graminis var. tritici in India. Proc. Indian Nat. Sci. Acad. 37B(6) 449=453. MEHTA, K.C. 1952. Further studies on cereal rusts in India Part II. Sci Monogr No. 18, Indian Counc. Agric. Res. pp. 365. |