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

Abstract

Foot rot disease caused by Phytophthora capsici is one of the most destructive diseases of black pepper in Vietnam and worldwide. However, many other oomycete species have also been recorded on this plant, and P. tropicalis and Pythium deliense were recently reported as serious threats to black pepper in India. On the other hand, 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 andthe 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 (ITS) region, then 11 isolates were further selected for the translation elongation factor 1-alpha (TEF1- α) and the beta-tubulin (TUB) gene analyses. Morphology and molecular analysesindicated that P. capsici, P. tropicalis, P. nicotianae, P. cinnamomi, P. parvispora, P. heveae, Phytopythium vexans, and a novel species of Phytopythium were clearly identified among oomycete isolates. Of these, P. capsiciand P. tropicalis could be the prevalent species in black pepper plantations in studied areas. The inoculation tests demonstrated that all the isolates of P. capsici, P. tropicalis and P. nicotianae were pathogenic on both leaves and roots of black pepper. Phytopythium vexans was pathogenic on root only. Meanwhile, P. cinnamomi, P. parvispora, P. heveae and Phytopythiumsp. were non-pathogenic.