Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands

Abstract

Most members of the oomycete genus Phytophthora are primary plant pathogens. Both soil- and airborne Phytophthora species are able to survive adverse environmental conditions with enduring resting structures, mainly sexual oospores, vegetative chlamydospores and hyphal aggregations. Soilborne Phytophthora species infect fine roots and the bark of suberized roots and the collar region with motile biflagellate zoospores released from sporangia during wet soil conditions. Airborne Phytophthora species infect leaves, shoots, fruits and bark of branches and stems with caducous sporangia produced during humid conditions on infected plant tissues and dispersed by rain and wind splash. During the past six decades, the number of previously unknown Phytophthora declines and diebacks of natural and semi-natural forests and woodlands has increased exponentially, and the vast majority of them are driven by introduced invasive Phytophthora species. Nurseries in Europe, North America and Australia show high infestation rates with a wide range of mostly exotic Phytophthora species. Planting of infested nursery stock has proven to be the main pathway of Phytophthora species between and within continents. This review provides insights into the history, distribution, aetiology, symptomatology, dynamics and impact of the most important canker, decline and dieback diseases caused by soil- and airborne Phytophthora species in forests and natural ecosystems of Europe, Australia and the Americas.

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

“…In South‐East Asia and Papua New Guinea, P. cinnamomi is usually in an equilibrium with the diverse, native forest vegetation or causes local dieback and mortality at most (Arentz, ; Arentz ; Arentz & Simpson, ; Jung, Chang, et al., ; Ko et al., ). In other continents, the situation is entirely different and introduced clonal P. cinnamomi A2 populations become invasive threatening a non‐coevolved flora and often causing dieback of whole ecosystems with high mortality rates (Brasier et al., ; Dos Santos et al., ; Jung, Vettraino, et al., ; Jung, Colquhoun, et al., ; Jung et al, ; McConnell & Balci, ; Shearer & Tippett, ; Vettraino et al., ). The results of the present survey indicate that the Valdivian rainforests are the most recent known entry in a long list of natural ecosystems threatened by P. cinnamomi A2 around the world.…”

“…In the Valdivian region, commercial Pinus radiata plantations have been established on a large scale. As the fine root system of P. radiata is susceptible to infections by P. cinnamomi eventually leading to little leaf disease and mortality (Newhook, ), the findings of P. cinnamomi in Valdivian rainforests could pose an additional threat to the P. radiata plantations which are already suffering from extensive needle infections and defoliations caused by the introduced airborne pathogen P. pinifolia (Durán et al., ; Jung et al, ). Prior to this study, P. cinnamomi has never been found associated with decline and dieback of natural forests in South America.…”

“…pathogenicity test (Arentz, 1983;Cartledge, Shaw, & Stamps, 1975;Weste, 1975). Extensive dieback and mortality of N. dombeyi stands in Patagonia, Argentina was considered to be induced by droughts (Suarez, Ghermandi, & Kitzberger, 2004 to infections by P. cinnamomi eventually leading to little leaf disease and mortality (Newhook, 1959), the findings of P. cinnamomi in Valdivian rainforests could pose an additional threat to the P. radiata plantations which are already suffering from extensive needle infections and defoliations caused by the introduced airborne pathogen P. pinifolia (Durán et al, 2008;Jung et al, 2018). Prior to this study, P. cinnamomi has never been found associated with decline and die- & Besoain, 2017;Rojic & Cancino, 1975).…”

“…In the soil infestation trial, all four tested isolates of P. cinnamomi proved to be highly aggressive to N. dombeyi and G. range plant pathogen, causing epidemic dieback and mortality of more than 3,000 woody species in natural ecosystems, nurseries and planted stands (Erwin & Ribeiro, 1996;Hardham, 2005;Jung et al, 2016Jung et al, , 2018. The global invasion and pandemic is almost exclusively driven by two clonal A2 lineages (Dobrowolski, Tommerup, & Blakeman, 2003), whereas in its supposed centre of origin in South-East Asia, both mating types of P. cinnamomi often co-occur and the genetic diversity of P. cinnamomi populations is high (Chang, Wang, & Wang, 1996;Jung, Chang, et al, 2017;Ko, Chang, & Su, 1978).…”

Investigations into the declining health of alder (Alnus glutinosa) along the river Lagan in Belfast, including the first report ofPhytophthora lacustriscausing disease ofAlnusin Northern Ireland

“…2). Symptoms include thinning foliage composed of small yellowing leaves, and bleeding cankers on the trunk, similar to the symptoms normally caused by other tree infecting Phytophthora species (Jung et al 2018). The aim of this research was to investigate the health status of Alnus along the river Lagan, and to assess if Phytophthora species were impacting on Alnus health.…”