In 2016 and 2017, surveys of
Phytophthora diversity were performed in 25 natural and semi-natural forest stands and 16 rivers in temperate and subtropical montane and tropical lowland regions of Vietnam. Using baiting assays from soil samples and rivers and direct isolations from naturally fallen leaves, 13 described species, five informally designated taxa and 21 previously unknown taxa of
Phytophthora were isolated from 58 of the 91 soil samples (63.7%) taken from the rhizosphere of 52 of the 64 woody plant species sampled (81.3%) in 20 forest stands (83.7%), and from all rivers:
P. capensis,
P. citricola VII, VIII, IX, X and XI,
P. sp. botryosa-like 2,
P. sp. meadii-like 1 and 2,
P. sp. tropicalis-like 2 and
P. sp. multivesiculata-like 1 from
Phytophthora major phylogenetic Clade 2;
P. castaneae and
P. heveae from Clade 5;
P. chlamydospora,
P. gregata,
P. sp. bitahaiensis-like and
P. sp. sylvatica-like 1, 2 and 3 from Clade 6;
P. cinnamomi (Pc),
P. parvispora,
P. attenuata,
P. sp. attenuata-like 1, 2 and 3 and
P. ×
heterohybrida from Clade 7;
P. drechsleri,
P. pseudocryptogea,
P. ramorum (Pr) and
P. sp. kelmania from Clade 8,
P. macrochlamydospora,
P. sp. ×insolita-like,
P. sp. ×kunnunara-like,
P. sp. ×virginiana-like s.l. and three new taxa,
P. sp. quininea-like,
P. sp. ×Grenada 3-like and
P. sp. ×Peru 4-like, from Clade 9; and
P. sp. gallica-like 1 and 2 from Clade 10. The A1 and A2 mating types of both
Pc and
Pr co-occurred. The A2 mating type of
Pc was associated with severe dieback of montane forests in northern Vietnam. Most other
Phytophthora species, including
Pr, were not associated with obvious disease symptoms. It is concluded that (1) Vietnam is within the center of origin of most
Phytophthora taxa found including
Pc and
Pr, and (2)
Phytophthora clades 2, 5, 6, 7, 8, 9, and 10 are native to Indochina.
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