The expression of pathogenicity-related genes in Phytophthora palmivora causing black pod rot disease on cacao (Theobroma cacao L.) in Indonesia

Phytophthora palmivora has a broad range of host plants. The expression of its pathogenicity-related genes in causing black pod rot disease on cacao in Indonesia has not been studied yet. This research was conducted to recognize relative expression of those genes using qPCR analysis. In planta experiment was carried out by inoculating representative three isolates on model plant (Nicotiana benthamiana) at the incubation periods of 24, 48, 72, and 96 h. The expressed genes were reconfirmed using conventional PCR and quantitatively analyzed using qPCR technique. The results showed that among eight target genes, four genes were actively expressed on the inoculated N. benthamiana, including CRN1, Pec1, Pec3, and RXLR5. Furthermore, qPCR analysis revealed that those genes were upregulated on the inoculated plants during incubation periods. In WNO1 and WAT1 isolates, the optimum expression was documented on the first day of incubation time, and then it was decreasing on the following days. However, the delay expression was exhibited by the pathogenicity-related genes in isolate BTG1. We assumed it as the general pathway of pathogenicity mechanisms in P. palmivora, since prior screening pathogenicity assay categorized that isolate BTG1 into moderate pathogenic, isolate WAT1 into high pathogenic, and isolate WNO1 into less pathogenic.