Differential expression of PR genes in response to Phytophthora capsici inoculation in resistant and susceptible black pepper (Piper nigrum L.) lines

Differential expression of three important genes encoding pathogenesis related proteins (PR proteins) viz. β-1,3-glucanase (PR-2), osmotin (PR-5) and cytosolic ascorbate peroxidase (cAPX, PR-9) were carried out in Phytophthora susceptible (Sreekara) and resistant (04-P24) black pepper lines compared to uninoculated plants using quantitative reverse transcription PCR (qRT-PCR). Upon Phytophthora capsici inoculation, expression of these three genes were either up-regulated or down-regulated. In the susceptible line, all three genes were expressed maximally on 1 day after inoculation (DAI) and thereafter the expression declined. In the resistant line, a steady increase in the expression pattern of genes was noticed during the course of infection. Highest expression levels of cAPX were noticed on 3 DAI and that of β-1, 3-glucanase and osmotin genes were maximum on 5 DAI. Soil inoculation of P. capsici affected the transcriptional activity of these genes in stem tissue also, indicating systemic defense response against the pathogen.