Pathogenic variability in Phytophthora capsici from black pepper (Piper nigrum L.) as revealed by transcriptome analysis

Phytophthora capsici, the causal organism of foot rot disease of black pepper exhibits wide variation in their virulence among the isolates. To understand the underlying mechanisms RNA-Seq analysis was carried out using a highly virulent (05-06) and less virulent (98-49) isolate of P. capsici from black pepper. The isolates were inoculated separately on the black pepper variety “IISR-Subhakara”, susceptible to Phytophthora and the leaf samples collected at 8, 24 and 48 h post inoculation (hpi) were subjected to RNA-Seq analysis. The isolates showed stage specific and infection responsive expression of various effectors and other proteins. The highly virulent isolate, 05-06 was found to be in biotrophic stage at 8 hpi and expressed various apoplastic and cytoplasmic effectors, the expression of which was several folds higher than that in less virulent isolate 98-49. By 24 hpi, the virulent isolate was in necrotrophic stage. The less virulent isolate 98-49, was also in biotrophic stage at 8 hpi and at 24 hpi it was in a stage of transition between biotrophic and necrotrophic phase and was in complete necrotrophic stage at 48 hpi. The over expression of various effector proteins and their tight temporal expression during the process of infection is the cause for the variation in virulence of the P. capsici isolates from black pepper. © 2018, Indian Phytopathological Society.