Abstract
Evaluation of rapeseed-mustard (Brassica spp.) under natural field conditions has revealed that there exists variation in rapeseed-mustard vars./lines available in Bangladesh towards infection by Alternaria brassicae (Berk) Sacc. and also there is variation in Alternaria blight incidence in different agro- ecological zones. Histopathological studies have established the fact that moderately thickened small sized cells of inner cortex are less affected and xylem vessels are not attacked by the pathogen at all and thus the invasion by A. brassicae is non-systemic. Var. BINA2 possesses those anatomical features. Healthy and less affected stem and siliqua of mustard contain higher amount of ascorbic acid, sugars and phenols which decline with increase in level of infection. Crops sown before November 5 can escape Alternaria blight severity. Incorporation of cowdung and gypsum into soil during land preparation also proved promising in reducing disease severity. Garlic extract completely inhibited mycelial growth of A. brassicae. Trichoderma harzianum and Pseudomonas fluorescens both in pure culture and talc formulation inhibited mycelial growth and spore germination of A. brassicae, increased mustard seed germination from 77 to 99%, increased seedling emergence by 20% and decreased seed infection of A. brassicae by 81%. Apparently healthy seeds when sown could alone decreased infection of A. brassicae by 23% and increase yield by 53%. Weeding, insecticide (Malathion 57 EC @ 0.2%) and fungicide (Rovral 50 wp @ 0.2%) when applied individually brought reduction of Alternaria blight severity by 24.8, 26.5 and 42% and increased yield by 8.00, 23.00 and 46.5% respectively, Plants raised from apparently healthy seeds when received one weeding, 2 sprays of insecticide and 2 sprays of fungicide had reduction in Alternaria blight severity by 21, 47 and 57% respectively. The application of these components increased seed yield by 57- 158%. Integration of the highest level of management i.e. apparently healthy seeds, one weeding, 2 sprays of insecticide and 2 sprays of Rovral 50 wp brought reduction in Alternaria blight severity by 92% and increased seed yield by 276%. Considering the cost involvement, integration of apparently healthy seeds, one weeding, one spray of Malathion 57 EC and one spray of Rovral 50 wp at 55 days age of the crop is recommended to secure an increase of seed yield by 231% through reducing PDI (Per cent Disease Index) by 77% and siliqua infection by 50%. Use of apparently healthy seeds proved to be the best component of the integrated management practices.