Spot blotch continues to cause substantial grain yield reductions under resource-limited farming conditions

Spot blotch caused by Cochliobolus sativus, is an important disease of wheat (Triticum aestivum) in the warm areas of South Asia. In the past, efforts have been made to improve spot blotch resistance in susceptible commercial cultivars. It is important to assess how much spot blotch-induced yield loss still occurs under resource-limited farming conditions using a newly released wheat cultivar. The outcome could underline further work needed towards breeding for foliar blight resistance. The present 2-year study was conducted to determine the reduction in grain yield and its components in a newly released Nepali wheat cultivar, Gautam, on resource-poor farms under a rice-wheat cropping sequence. Spot blotch severity went up to 100% and 70% in 2004 and 2005 respectively. The use of the fungicide Opus (epoxiconazole) reduced disease severity to below 10% suggesting its value in controlling spot blotch in the absence of highly spot blotch resistant wheat cultivars. Grain yield loss due to spot blotch ranged from 4% to 38% and 25% to 43% in 2004 and 2005 respectively. Thousand-kernel weight and the number of kernels per spike were reduced respectively by 15% and 10% in 2004 and by 18% and 11% in 2005. The study shows that the level of resistance to spot blotch in the new cultivar Gautam represents a partial accomplishment in breeding for resistance over the past decade. The findings underscore the need for further research support for improving genetic resistance against spot blotch in wheat to increase food security among resource-poor farmers in the eastern Gangetic plains in South Asia and reduce the yield loss caused by this disease.