Cross-Infection Analysis of Phytophthora spp. Isolated from Cacao (Theobroma cacao L.) Pods at Nagcarlan, Laguna, Philippines

Despite its high demand, the production of cacao ( Theobroma cacao L.) remains low, which can be attributed to phytopathogens responsible for the destruction of cacao crops. Among these phytopathogens include Phytophthora spp. - pathogenic oomycetes that target plant species through their zoospores and cause black pod rotting. This research studied the ability of Phytophthora spp. to infect fruits commonly intercropped with cacao, such as papaya ( Carica papaya L.) and banana ( Musa spp.). Cacao pods exhibiting black pod rot symptoms were collected to isolate Phytophthora spp. from two cacao farms in Nagcarlan, Laguna, Philippines. Twenty-two isolates were identified as Phytophthora palmivora through their culture morphology, zoospore morphology, and molecular identity through ITS gene sequencing and confirmed through phylogenetic analysis. Five selected isolates were inoculated with their original host, cacao, and cross-infected with banana and papaya, which exhibited varying degrees of black pod rot symptoms. The lesions in cacao exhibited a higher degree of disease progression compared to banana and papaya. However, statistical analysis showed that bananas were more susceptible to the infection than papayas. Quantifying the degree of infection of P. palmivora from its host to commonly intercropped plants provides information on which plants are most vulnerable to infection within intercrop systems.