Host Resistance of Genotypes of Rapeseed and Mustard against Alternaria blight Under the Agro-ecological Conditions of Undulating Red and Lateritic Belt of West Bengal

Alternaria blight caused by Alternaria brassicae (Berk.) Sacc. has been reported to be most wide spread and destructive fungal disease of rapeseed-mustard throughout the world. It has a drastic effect on various yield components of rapeseed and mustard which is reflected in reduction of yield up to the tune of fifty percent. Indiscriminate use of fungicides not only pollute the environment but has an adverse residual effect on soil health and soil fertility. Lack of awareness regarding application of these chemicals, their doses, and timing of spray further aggravated the situation. Experiments were conducted to identify a suitable genotype having enough resistance against the disease under the Undulating Red and Lateritic agro-climatic zone of West Bengal with a view to minimize the use of hazardous chemicals. Nine varieties of rapseed-mustard were grown under natural environmental conditions for evaluating their resistance against Alternaria blight. Genotypes Bhagirathi and Kalyan were found to be ‘Moderately Resistant’ against Alternaria blight with percent disease index of 19.52 and 17.64 percent (for leaves) and 13.53 and 11.89 percent (for pods) in 2011-12 which was collinear in the successive year i.e. 2012-13 with percent disease index of 17.42 and 15.54 percent (for leaves) and 12.05 and 11.53 percent (for pods) respectively for the two germplasms. Genotypes namely Varuna, Panchali, Agrani and B-9 came under the ‘Highly Susceptible’ reaction group with PDI in the range of 58-62% for leaves. Germplasms Seeta and Jhumka were noticed Moderately Susceptible, while, genotype Sarma was reported to be Susceptible in this region. The present study not only validated the resistant sources against Alternaria blight based on different morphological parameters but also provided an elementary idea regarding sowing of resistant genotypes to farmers so that the indiscriminate application of various chemicals can be reduced to a great extent on one hand and an increased yield could be obtained on the other.