Virulence structure of wheat powdery mildew pathogen, Blumeria graminis tritici: a review

Wheat crop is inflicted by a large number of fungal pathogens at its various growth stages leading to huge yield losses, among which powdery mildew (PM) inflicted by Blumeria graminis f. sp. tritici ( Bgt ) is the most important and widely prevalent disease. The disease management can be partially achieved with the application of fungicides. However, the resource starved small and marginal farmers in the developing and under developed countries cannot afford costly spray schedules. Moreover, there is growing awareness regarding the residual toxicity resulting into soil, water and environmental pollution as a result of excessive use of fungicides and appearance of strains resistant to pesticides. The host resistance to PM is an eco- and farmers friendly, cost effective, practically viable and highly preferred alternative for its management. The life cycle of the pathogen compels the fungus to undergo changes in virulence, to enable the infection of resistant cultivars. Understanding the virulence structure and genetic diversity of Bgt is crucial to develop wheat varieties with stable and durable resistance and their proper deployment, but, the information on genes responsible for resistance remains subtle. This present review is an attempt to review and understand the virulence pattern of the Bgt populations in epidemiological important areas of the world. Virulence structure of Bgt is highly complex and diverse and PM resistance in wheat cultivars can easily be overcome by the Bgt populations with new and matching virulences, leading to severe epiphytotics under congenial agro-climatic conditions. The global virulence pattern studies, revealed that Pm resistance genes are defeated. Moreover, a thorough understanding of the PM disease with respect to specific focus on the host–pathogen relationship of Bgt -wheat is the key element in the development of resistant varieties, germplasm and introduction of new donors of wheat with Pm resistance genes which is essential to incorporate diverse and stable resistance genes into wheat breeding material.