Current species of oomycetes associated with foot rot disease of black pepper in Vietnam

Foot rot disease caused by Phytophthora capsici is one of the most destructive diseases of black pepper in Vietnam and worldwide. However, other oomycete species such as P. tropicalis and Pythium deliense reported as serious threats to black pepper in India have also been recorded on this plant. The population of oomycetes occurring in black pepper plantations in Vietnam and their pathogenicity have not been investigated in the last decade. To this end, two hundred fifteen oomycete isolates were collected from the root rots and rhizospheric soil of black pepper in the Central Highlands and the Southeast region of Vietnam. Of these, 23 isolates were representatively chosen based on their origin and morphology for DNA sequence analysis of the internal transcribed spacer region, then 11 isolates were further selected for the translation elongation factor 1-alpha and the beta-tubulin gene analyses. Morphology and molecular analyses indicated that P. capsici, P. cinnamomi, P. heveae, P. nicotianae, P. parvispora, P. tropicalis, Phytopythium vexans, and a new species candidate Phytopythium sp. were identified among oomycete isolates. Of these, P. capsici and P. tropicalis could be the prevalent species in black pepper plantations in studied areas. The inoculation tests demonstrated that P. capsici, P. nicotianae and P. tropicalis were pathogenic on both leaves and roots of black pepper. Phytopythium vexans was pathogenic on root only. Meanwhile, P. cinnamomi, P. heveae, P. parvispora and Phytopythium sp. were non-pathogenic.