Morphological and molecular identification of Phytophthora and its virulence in vitro on cocoa shoots (Theobroma cacao L.)

Abstract

This study analyzed two strains of Phytophthora (PP8 and PPAGR) isolated from cacao (Theobroma cacao) pods showing characteristic symptoms of black pod disease, collected in the province of Los Ríos, Ecuador. Molecular analysis using primers targeting the ITS1, 5.8S, and ITS2 regions (ITS4 - ITS6), along with sequencing of the amplified product, identified both strains as P. palmivora. Additionally, the virulence of the strains was assessed by inoculating them into shoots of Nacional Fino de Aroma and CCN-51 cacao varieties. A completely randomized factorial design with seven replicates was used, considering each cacao shoot as an experimental unit. The results showed that strain PP8 exhibited 100% incidence and severity in Nacional Fino de Aroma cacao shoots, demonstrating a high susceptibility to Phytophthora. Furthermore, strain PP8 was found to infect only Nacional cacao shoots, whereas CCN-51 cacao shoots remained unaffected by either strain. In conclusion, the impact of Phytophthora depends on both the virulence of the isolate and the cacao variety.