Genotype specific host resistance for Phytophthora in black pepper (Piper nigrum L.)

Phytophthora foot rot is a devastating disease in black pepper which is caused by P. capsici. Using host resistance is a major component in the integrated pest management of this disease. To explore the host resistance pattern, we studied the genotype specific differential expression of important pathogenesis related gene β 1, 3 glucanase and 5 R gene loci from resistant and susceptible varieties of black pepper. The relative expression of β 1, 3 glucanase was up regulated in resistant variety and down regulated in susceptible variety. R gene loci Pn CNBS 5, CNBS 3 and Pn CNBS 2 showed up regulation in susceptible variety in the early hours of infection while resistant genotype recorded its down regulation till 72 h suggesting that the selective down expression of these loci may be attributed to the resistance in the resistant variety. These R genes may be the susceptibility genes (S-genes) in black pepper for Phytophthora. The high relative expression of the R gene locus Pn CNBS 4 and Pn CNBS 1 in resistant genotype at early hours shows their involvement in resistance towards P. capsici. The differential expression of the R gene loci shows the genotype specific functional significance for Phytophthora resistance.