Molecular analysis reveals that lack of chasmothecia formation in Erysiphe necator in Maharashtra, India is due to presence of only MAT1-2 mating type idiomorph.

Abstract

The heterothallic, ubiquitous fungus Erysiphe necator causes powdery mildew disease of grapevines and in many countries it is reported to reproduce both asexually and sexually. Sexual reproduction results in the formation of chasmothecia (cleistothecia) on infected surfaces when the colonies of two opposite mating types meet on the infected plant parts and the temperatures are favorable for their development. Chasmothecia are reported from north India, but not from peninsular India, even though powdery mildew is reportedly present in these regions at least since the beginning of the last century. Through systematic survey of ten vineyards in Maharashtra and adjoining Karnataka in peninsular India, we confirmed the absence of chasmothecia under natural conditions. Analysis of temperature data from two locations in Maharashtra showed that the Tmax and Tmin were favourable for chasmothecia initiation (10 °C to 30 °C) and maturation (15 °C to 30 °C) for a sufficient period of time. Multiplex PCR of 120 E. necator field isolates collected from peninsular India showed presence of a single band of 232 bp corresponding to MAT1-2 mating type idiomorph or MAT- phenotype. None of the samples gave band of 408 bp corresponding to MAT1-1 mating type idiomorph. Further, two bands of 408 bp and 232 bp were detected in only one powdery mildew sample collected from Kashmir, in north India while the other nineteen samples gave a single band of 232 bp. Thus, molecular analysis established that E. necator is not sexually reproducing in Maharashtra due to presence of only one mating type idiomorph. The study also brings out that MAT1-1 mating type idiomorph is not as common in nature as MAT1-2 and explains why in many other countries, too, chasmothecia were first observed as late as half to one century after start of grape cultivation.