DIVERSITY OF PHYTOPHTHORA SPECIES IN NATURAL FORESTS AND STREAMS AND IN RUBBER PLANTATIONS IN VIETNAM

Many devastating tree declines are driven by non-native Phytophthora species which remain
unnoticed in their native environment and after introduction to other continents became
invasive, threatening a non-coevolved highly susceptible flora. There is an accumulating
body of evidence that many important Phytophthora pathogens with global distribution are
native to Southeast Asia suggesting this region might be one center of origin of the genus
Phytophthora. Therefore, a 5 weeks Phytophthora survey was conducted in spring 2016 in 23
forest stands (tropical rainforests and montane forests) between 12 and 2903 m altitude in 4
National Parks, in 10 natural rivers and streams and in 14 rubber tree plantations across
Vietnam. Using classical and molecular identification, the 793 oomycete isolates obtained
could be assigned to 18 known species and informally designated taxa of Phytophthora, 21
new Phytophthora taxa, a diverse array of known and new taxa of Phytopythium, Pythium
and Elongisporangium including 15 genotypes from the Phytopythium vexans complex, and
a new sister genus of Phytophthora which is informally designated as Nothophytophthora
gen. nov. The results from the Vietnamese survey contribute to clarify the origin of the two
most destructive invasive Phytophthora pathogens of trees and natural ecosystems. Detailed
morphological and physiological studies, sequencing of additional gene regions and
multigene phylogenetic analyses are underway to characterise and officially describe the
new Phytophthora species from Vietnam and the new genus Nothophytophthora. Soil
infestation trials will be performed to test the potential threat posed by new Phytophthora
species from Vietnam to European forests.