Natural Incidence and Genetic Variability of Erysiphe pisi, the Causal Agent of Powdery Mildew on Peas in the Nilgiris District, Tamil Nadu, India

Erysiphe pisi, which causes pea powdery mildew, is an obligate biotrophic pathogen that can easily adapt to its host plant. Understanding the natural incidence and genetic variations of the pathogen is essential for disease control and for breeding resistant variety to pea powdery mildew. The incidence was studied in different locations of the Nilgiris district, and the disease recorded from 32.61 to 45.55 and 14.08 to 20.84 per cent in leaves and pods, respectively. A total of 10 isolates of E. pisi were obtained from the diseased samples to study the genetic variability if any, among them using internal transcribed spacer region amplification and inter-simple sequence repeats (ISSRs). PCR amplification of total genomic DNA with ISSR primers generated unique banding patterns depending upon primers and isolates. Twelve oligonucleotide primers were selected for the ISSR assays, which resulted in 742 bands for ten isolates of E. pisi. The number of bands obtained was entered into a PRIMER 7 to understand genetic relationship and Bray-Curtis coefficient for hierarchical cluster analysis. The results showed that the variability among the pathogen isolates was moderate. The above ten isolates were grouped into two major clusters and one single cluster had an average Polymorphic Information Content value (PIC) of 0.883 and Effective Multiplication Ratio (EMR) of 90. Hence, it is inferred that the E. pisi infecting peas in the Nilgiris consists of a single clonal lineage with a moderate level of genetic diversification.