Genetic diversity, mating type and pathogenicity of two Phytophthora species infecting black pepper in India

Abstract

Phytophthora capsici and P. tropicalis are the two species of Phytophthora associated with foot rot disease of black pepper in India. High genetic diversity amongst the Phytophthora species contributes to its wide host range and variability in the virulence pattern. In the present study, genetic diversity of Phytophthora species infecting black pepper was analysed using RAMS (Random Amplified Microsatellites) and REP (Repetitive Extragenic Palindromic)-PCR fingerprinting. Forty-eight isolates, 24 each of P. capsici and P. tropicalis collected from major black pepper growing states, such as Karnataka, Kerala, Tamil Nadu and Goa, were used in the study. The analyses revealed a total of 160 loci of which 150 (93.75%) were polymorphic. UPGMA cluster and PCoA analysis based on combined RAMS and REP-PCR data clearly grouped the P. capsici and P. tropicalis isolates into two clusters which were further divided into four sub-clusters viz., I & II (P. capsici) and III & IV (P. tropicalis). The study clearly indicated that all the isolates were genetically unique and the entire population was heterogeneous. REP-PCR primers showed more polymorphic loci than RAMS primers. Further, sixteen isolates were selected for morphological and infectivity analyses under in vitro conditions. The isolates exhibited varied colony morphology, sporangial shapes and belonged to A1 mating type. Under in vitro conditions, all the sixteen black pepper Phytophthora isolates could infect nutmeg, tomato, chilli, pumpkin, and cucumber and few of the isolates could infect cardamom. None of the isolates could infect coconut, areca nut and vanilla.