Prevalence of sterility mosaic disease (SMD) and variability in pigeonpea sterility mosaic virus (PPSMV) in southern-India

Sterility mosaic disease (SMD) is a major problem for pigeonpea production in the Indian subcontinent. A comprehensive and systematic survey was carried out to determine the incidence of pigeonpea sterility mosaic disease (SMD) and variability among disease causing agents in Andhra Pradesh, Karnataka, Tamil Nadu and Telangana states of southern India during the 2017 rainy season. The results indicate a huge variation in SMD incidence ranging from 0 to 47.50% among the surveyed states and also within the states. Further, the phylogenetic analysis of the RNA-3 sequence of disease causing two viral agents such as PPSMV-I and PPSMV-II exhibited considerable variability among seven different geographical strains representing four states in southern India. RNA-3 sequence of PPSMV-I of Bengaluru, Tirupathi, Vamban, and Coimbatore isolates clustered together, while Gulbarga isolate distinctly separated out. Similarly, a RNA-3 sequence of PPSMV-II of Vamban isolate was separated out from the rest of the cluster. There is a separate existence of PPSMV-II alone alongside mixed infection of PPSMV-I and PPSMV-II in southern India. The samples from Patancheru location were positive for PPSMV-I and PPSMV-II, whereas one sample from Bengaluru and four samples from Coimbatore location were found positive for PPSMV-II only and the rest of the samples were positive for both the viruses. None of the sample was positive for PPSMV-I alone. Overall our study provides evidence of variability in SMD causing agents which is critical in developing precise diagnostic tools and stable management strategies in pigeonpea.