DEVELOPMENT, ISSUES AND STRATEGIES FOR THE MANAGEMENT OF POTATO LATE BLIGHT

Abstract

Even after more than 150 years of Irish potato famine, potato late blight caused by a fungus like organism, Phytophthora infestans, continues to be the major bottleneck in realizing the desired potato production across the globe. During the last two-decade, P. infestans, population structure and biology has undergone a sea change which has added new dimension to late blight epidemiology and its management. As a result of series of migrations of P. infestans from its center of origin, central Mexico, new pathogen< populations hitherto restricted to central Mexico only were introduced to rest of the world. The new population consists of both A₁ and A₂ mating types, having increased diversity with regard to virulence factors and which is predominantly tolerant to metalaxyl fungicide and it is comparatively more aggressive than the old popualtion and is at the verge of displacing it at several locations. Presence of both A₁ and A₂ mating types have led to sexual reproduction and consequently production of thick- walled oospores which serve as primary source of the disease. The issues and concerns that arise out of the introduction of new population includes breakdown of host resistance, early initiation of disease epidemics, redundance of use of metalaxyl based fungicides in managing the disease, increased chance of infection at sub-optimal temperature in combination with shorter leaf wetness periods and high speed of spread of epidemics arising out of population having shorter latent periods. Consequently, the window of opportunity for action by potato growers has narrowed down. Therefore, new diseases management strategies are called for checking the ‘new blight’ initiated by the new P. infestans population. This would call for development of modern methods of detection of the pathogen during storage and transit, cataloguing and characterization of the pathogen population across the globe, identifying the areas where sexual reproduction is in place and working out its implications on disease epidemics, management of soil borne inoculum in the form of thick-walled oospores, development of site-specific forecasting and Decision Support System (DSS) and development of varieties having high degree of field resistance through marker assisted selection.