IDENTIFICATION OF PHYTOPHTHORA SPECIES INFECTING CITRUS IN VIETNAM.

In a survey aimed at identifying Phytophthora species infectingfruit crops in Viet Nam, P. citrophthora and P. nicotianae were thespecies most commonly recovered from soil and trees in citrus plantations.P. nicotianae was prevalent in citrus groves in the Ben Treand Tien Giang provinces (southern Viet Nam). Interestingly, bothA1 and A2 mating types of the latter species were found, while inother citrus-growing areas of the world, such as the Mediterraneanregion, South Africa, Australia and the Americas, A1 is the onlymating type occurring in citrus groves, suggesting southern-eastAsia could be a centre of origin of this Phytophthora species. Mixedinfections of three Phytophthora species were detected on the fruitsof pomelo (Citrus grandis) with symptoms of brown rot collected inthe Mekong Delta region (southern Viet Nam). The three specieswere identified as P. colocasie, P. insolita and P. meadii on the basisof morphological characters and DNA analysis. The ITS-rDNA sequenceof three representative isolates obtained from pomelo fruitsshowed 99, 99 and 100% similarity with reference ITS-rDNA sequencesof P. colocasie, P. insolita and P. meadii from GenBank,respectively. Koch’s postulates were fulfilled by pathogenicity testson fruits of pomelo and other citrus species. To our knowledge, thisis the first report of natural infections of these three Phytophthoraspecies on citrus fruits worldwide and the first report of P. insolitain VietNam.