Responses of European Forests and Society to Invasive Pathogens

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Worldwide forest surveys reveal forty-three new species in Phytophthora major Clade 2 with fundamental implications for the evolution and biogeography of the genus and global plant biosecurity

Publication . Jung, T.; Milenković, I.; Balci, Y.; Janoušek, J.; Kudláček, T.; Nagy, Z. Á.; Baharuddin, B.; Bakonyi, J.; Broders, K. D.; Cacciola, S. O.; Chang, T.-T.; Chi, N. M.; Corcobado, T.; Cravador, Alfredo; Đorđević, B.; Durán, A.; Ferreira, M.; Fu, C.- H.; Garcia, L.; Hieno, A.; Ho, H.- H.; Hong, C.; Junaid, M.; Kageyama, K.; Kuswinanti, T.; Maia, Cristiana; Májek, T.; Masuya, H.; Magnano di San Lio, G.; Mendieta-Araica, B.; Nasri, N.; Oliveira, L. S. S.; Pane, A.; Pérez-Sierra, A.; Rosmana, A.; Sanfuentes von Stowasser, E.; Scanu, B.; Singh, R.; Stanivuković, Z.; Tarigan, M.; Thu, P. Q.; Tomić, Z.; Tomšovský, M.; Uematsu, S.; Webber, J. F.; Zheng, H.- C.; Zheng, F.- C.; Brasier, C. M.; Horta Jung, M.

During 25 surveys of global Phytophthora diversity, conducted between 1998 and 2020, 43 new species were detected in natural ecosystems and, occasionally, in nurseries and outplantings in Europe, Southeast and East Asia and the Americas. Based on a multigene phylogeny of nine nuclear and four mitochondrial gene regions they were assigned to five of the six known subclades, 2a-c, e and f, of Phytophthora major Clade 2 and the new subclade 2g. The evolutionary history of the Clade appears to have involved the pre-Gondwanan divergence of three extant subclades, 2c, 2e and 2f, all having disjunct natural distributions on separate continents and comprising species with a soilborne and aquatic lifestyle and, in addition, a few partially aerial species in Clade 2c; and the post-Gondwanan evolution of subclades 2a and 2g in Southeast/East Asia and 2b in South America, respectively, from their common ancestor. Species in Clade 2g are soilborne whereas Clade 2b comprises both soil-inhabiting and aerial species. Clade 2a has evolved further towards an aerial lifestyle comprising only species which are predominantly or partially airborne. Based on high nuclear heterozygosity levels ca. 38 % of the taxa in Clades 2a and 2b could be some form of hybrid, and the hybridity may be favoured by an A1/A2 breeding system and an aerial life style. Circumstantial evidence suggests the now 93 described species and informally designated taxa in Clade 2 result from both allopatric non-adaptive and sympatric adaptive radiations. They represent most morphological and physiological characters, breeding systems, lifestyles and forms of host specialism found across the Phytophthora clades as a whole, demonstrating the strong biological cohesiveness of the genus. The finding of 43 previously unknown species from a single Phytophthora clade highlight a critical lack of information on the scale of the unknown pathogen threats to forests and natural ecosystems, underlining the risk of basing plant biosecurity protocols mainly on lists of named organisms. More surveys in natural ecosystems of yet unsurveyed regions in Africa, Asia, Central and South America are needed to unveil the full diversity of the clade and the factors driving diversity, speciation and adaptation in Phytophthora.

2024-03Journal article

Open access

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

Publication . Jung, Thomas; Durán, Alvaro; Stowasser, Eugenio Sanfuentes von; Schena, Leonardo; Mosca, Saveria; Fajardo, Sebastian; González, Mariela; Navarro Ortega, Angella D.; Bakonyi, Jozsef; Seress, Diana; Michal Tomšovský; Cravador, Alfredo; Maia, Cristiana; Marilia Horta Jung; Horta Jung, Marília; Jung, Thomas; Cravador, Alfredo

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.

2018-05Journal article

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