Epidemiology of Puccinia Triticina in Gangetic Plain and planned containment of crop losses

Leaf or brown rust of wheat incited byPuccinia triticinaEriks. is the most important one. The pathogen spreads across national boundaries, virulences get mixed and the disease severity level reached does affect the crop productivity. The Gangetic Plain (GP) being warmer sowing is done in November and wheat is harvested by mid April. The 18 million hectares under wheat in this area is predominantly irrigated and well fertilized having a cultivar mosaic of at least 30 or more genotypes differing for their leaf rust resistance. The primary inoculum source is the Cental Himalaya (CH) of Central Nepal and here the CIMMYT sponsored activities have promoted varietal diversification. Shift in sowing time and cultivation of several varieties differing in resgene combination over eastern GP has delayed the process of establishment of the primary foci of leaf rust here before January end. Insufficient inoculum multiplication then curtails the spread of urediospores westward beyond Delhi. Build up of disease severity levels to epidemic proportions gets delayed by at least two weeks. As a consequence of this temporal delay, wheat gets harvested before the severity could inflict crop losses. Occasional inter-zone exchange of inoculum before the crop harvest facilitates the injection of new virulences