Spot blotch disease of wheat – a new thrust area for sustaining productivity

Abstract

Spot blotch caused by Bipolaris sorokiniana is a major disease of wheat in warm and humid regions of the world including South East Asian countries such as India, Nepal and Bangladesh. The fungus has a worldwide distribution but as a pathogen it is the most aggressive under the conditions of high relative humidity and temperature associated with the low fertility of soils in South Asia, South America, Africa, and Australia. The yield loss due to the disease is very significant especially in North Eastern Plains Zone (NEPZ) of India, Nepal Terai and North Western Bangladesh. Early symptoms are characterized by small, dark brown lesions ranging 1 to 2 millimeter long without chlorotic margin. In susceptible genotypes, these lesions extend very quickly in oval to elongated blotches, light brown to dark brown in colour. They may reach several centimeters before coalescing and inducing the death of the leaf. The pathogen has morphological and molecular variations among the isolates. Ideal conditions for spot blotch development on the leaves are relative humidity of near 95 per cent with an average temperature in the coolest month above 17°C and long periods (more than 12 to 18 hours) of leafs wetness caused by rainfall, irrigation, fog or dew. Recently a number of genotypes have been identified as donors for improving host resistance. The best way to control spot blotch is through an integrated approach including varietal replacement, agronomic management and need based application of fungicides. The use of molecular tools in identifying QTLs for spot blotch resistance, pathogenic variability and exercising marker assisted selection has good scope for effective management of this pathogen for ensuring food security in the world.