Distribution and comparative studies of Phytophthora diseases of coconut (Cocos nucifera L.) in the Philippines

Severe cases of coconut bud rot and the eventual death of affected palms particularly on MAWA hybrid plantations created a serious problem in the coconut industry. Epidemic areas were identified in three provinces of Mindanao [Philippines] namely; Camiguin Is., Davao del Sur and Davao del Norte. Likewise, thousands of bud rot cases were reported in two big coconut plantations in Davao del Sur, both planted to MAWA hybrids. Approximately 10,100 palms were destroyed by the disease from 1987 to 1989. Cases of fruit rot infection were also reported and found to be common on red and yellow colored cultivars, also observed of MAWA hybrids causing low coconut production. Symptoms of bud rot is wilting of the youngest leaf accompanied by dry rotting and leaf bases, aggravated by bacterial contamination that results to decay of the growing plant. Affected nuts manifest the typical symptoms characterized by irregular brown patches on the epicarp and husk with undeveloped albumen/copra at advanced stage. The cause of the diseases is tentatively identified to be Phytophthora palmivora due to limited taxonomic characters to describe the exact nature of the species of Phytophthora associated with both diseases. Inoculation of seedlings and detached young nuts using sporangial suspension of P. palmivora culture resulted in the development of the disease symptoms which proved the pathogenicity of the isolates. Comparative studies of the symptoms and etiology of the disease on both seedlings and young nuts revealed differences on the mode of attack and virulence of the P. palmivora isolates, but no clear distinction was established. Results of cross-inoculation test suggest that there exists a specific host-parasite interaction in respective plant part invaded by the pathogen. The methods used to inoculate the seedlings and young nuts used in the study proven to be effective can be used as a tool in the conduct of resistance study to test varietal reaction of different coconut cultivars to fungus infection