Diversity of Phytophthora species in Valdivian rainforests and association with severe dieback symptoms

Abstract

The Valdivian rainforest, one of the global hotspots of biodiversity, is a temperate rainforest originating as a Tertiary relic from the supercontinent Gondwana. In November 2014, a survey of Phytophthora diversity was performed in 13 natural forest stands and 20 forest streams and rivers in two protected areas near Valdivia and in a temperate montane forest in the Concepción area. One planted stand each of the introduced tree species Castanea sativa and Fagus sylvatica were also included. Using baiting assays, eight described species and four previously unknown taxa of Phytophthora were isolated from 86% of the 50 rhizosphere soil samples from seven of the eight tree species sampled in 12 forest stands, and from 20 streams: P. chlamydospora, P. cinnamomi, P. kernoviae, P. lacustris, P. plurivora, P. pseudosyringae, P. ×cambivora, P. ×stagnum, P. valdiviana nom. prov. from Clade 2b, P. madida nom. prov. from Clade 8a, and P. chilensis nom. prov. and P. pseudokernoviae nom. prov. The latter two species are the closest relatives of P. kernoviae from Clade 10. Phytophthora pseudokernoviae nom. prov. was also isolated from necrotic leaves of Drimys winteri. From the Valdivia river, a swarm of three Clade 6 hybrids was recovered. Each hybrid isolate resulted from multiple reticulation events with P. thermophila as maternal and both P. amnicola and P. chlamydospora as paternal parents. In addition, three previously unknown and recently described Nothophytophthora species, N. caduca, N. chlamydospora and N. valdiviana, were isolated from several forest streams. Phytophthora cinnamomi, the most common and widespread species in soils of native forests, was associated with severe dieback of Valdivian rainforest trees, in particular D. winteri, Luma apiculata, Nothofagus dombeyi and the endangered Saxegothaea conspicua. A first pathogenicity test demonstrated high aggressiveness of P. cinnamomi to several native tree species, including N. dombeyi, Blepharocalyx cruckshanksii and Gevuina avellana.

A Survey in Natural Forest Ecosystems of Vietnam Reveals High Diversity of both New and Described Phytophthora Taxa including P. ramorum

“…In recent years, an impressive diversity of both known and previously unknown Phytophthora species has been revealed from stream surveys in several countries, including the eastern and western USA, Chile, Australia, South Africa and Taiwan [10,11,14,17,18,44,61], as discussed previously [10]. By comparison the riparian Phytophthora communities identified here in Vietnam are remarkably rich, with seven described species, five informally designated taxa and 12 previously unknown taxa.…”

“…The ITS sequences of P. sp. meadii-like 2 showed intraspecific variability at positions 11,13,22. Most isolates differed from P. sp.…”

“…For the isolation of Phytophthora spp. from the 16 rivers and streams, an in-situ baiting technique was used [10,11]. Twelve of the 16 riparian baiting sites were located inside or downstream of natural forests (Figure 2c).…”

“…The number of devastating declines of trees and other woody plants driven by introduced invasive Phytophthora species in natural ecosystems in Australia, Europe, and North America has increased exponentially since the 1960s [1][2][3][4][5][6][7][8][9]. Therefore, numerous surveys in natural and semi-natural ecosystems have been performed in the past two decades to assess Phytophthora diversity in these continents and in Africa, Asia, and South America [4,5,[10][11][12][13][14][15][16][17][18][19]. As a result of these surveys and molecular re-evaluations of culture collections and several species complexes, the number of described species and informally designated taxa of Phytophthora has tripled since 1999 [2,18,[20][21][22][23][24][25][26][27][28].…”

Site‐specific distribution of oak rhizosphere‐associated oomycetes revealed by cytochrome c oxidase subunit II metabarcoding

“…The majority of studies designed to detect Oomycetes involved in the decline have used cultivation based techniques and detected a high site variability for targeted pathogens (Duque-Lazo, van Gils, Groen, & Navarro-Cerrillo, 2016;Jung et al, 2018;Linaldeddu, Scanu, Maddau, & Franceschini, 2014;Pérez-Sierra et al, 2013;Romero et al, 2007). For example in south-western Spain and southern Portugal, sometimes the pathogens, P. cinnamomi and Globisporangium spiculum, coexisted, while at other sites, only one pathogen dominated (Romero et al, 2007).…”