The susceptibility of rare and threatened NSW species to the root-rot pathogen Phytophthora cinnamomi: 1. Initial testing and identification of key research questions

Abstract

In Australia disease caused by Phytophthora cinnamomi can have devastating impacts on native vegetation, especially on plant species with restricted distributions. The identification of susceptible threatened species is a crucial first step in understanding disease aetiology and selecting appropriate management. In a glasshouse trial, plants of 16 rare and threatened New South Wales native species from 10 families were inoculated with the pathogen. Phebalium squamulosum spp. alpinum was included as a susceptible control. We found that three species are highly susceptible to the pathogen (Nematolepis rhytidophylla (Albr. & N.G.Walsh) Paul G.Wilson, Prostanthera marifolia R.Br., Pultenaea sp. ‘Genowlan Point’); four others (Hibbertia spanantha Toelken & A.F.Rob, Phebalium bifidum P.H.Weston & M.J.Turton, Plinthanthesis rodwayi (C.E.Hubb.) S.T.Blake, Pomaderris delicata N.G.Walsh & Coates) are likely to be susceptible based on symptoms. The remaining species had few or no plant deaths and no pathogen recovery from the roots. All of the species regarded as highly susceptible are known from single populations. Following these results, subsequent research will assess the efficacy of prophylactic treatment on highly susceptible threatened species, and test whether glasshouse tests are indicative of field responses. Other threatened species will also be tested for susceptibility.

The susceptibility of rare and threatened NSW species to the root-rot pathogen Phytophthora cinnamomi: 2. The identification of species requiring protection or further research

“…Phebalium squamulosum ssp. alpinum was found to be highly susceptible to P. cinnamomi (and clearly symptomatic when infected) in previous tests under similar glasshouse conditions (Rigg et al 2018;Wan et al 2019), and so was chosen as a positive control.…”

“…Between 2019 and 2022, we tested 32 species listed as threatened under the NSW Biodiversity Conservation Act 2016, and occurring predominantly on the coast and tablelands of eastern NSW, for susceptibility to P. cinnamomi infection (Table 1), Dracophyllum macranthum was listed as vulnerable at the time of testing in 2020, but delisted in 2021. Our intention, as stated in Wan et al (2019), was to give preference to species occurring in one to a few populations, but species selection was largely governed by availability of plant material for propagation. All plants were grown at Australian National Botanic Gardens, Canberra, and the Australian Botanic Gardens, Mount Annan; Banksia conferta, Dillwynia tenuifolia, Dracophyllum macranthum, Isopogon fletcheri and Pultenaea aristata were grown from seed, whereas all other species were grown from cuttings.…”

“…In the first paper in this series (Wan et al 2019), we investigated the susceptibility of 16 New South Wales (NSW) threatened plant species to the pathogen Phytophthora cinnamomi Rands in glasshouse inoculation tests; seven species were found to be infected under the conditions of the tests, three of which developed severe disease leading to mortality. We also outlined the research identified at that time for a better understanding of the threat of the pathogen and how the threat might be mitigated.…”

Soil chemistry and fungal communities are associated with dieback in an Endangered Australian shrub

“…Directly linking observed responses to specific dieback drivers in ecological experiments can be difficult. That is, if the pathosystem is not known, traditional experimental approaches such as susceptibility or manipulation studies may not be feasible as field environments often possess complex disease etiologies (Scarlett et al 2013 ; Wan et al 2019 ). Bioassays involving plants grown under controlled conditions and inoculated with field soils from healthy and dieback-affected individuals are a useful tool to begin to understand plant-dieback interactions.…”

“…"Dieback" is linked to some of these instances, and involves the partial (e.g., roots, shoots) or entire death of a plant over time. Dieback is of growing concern for the conservation of many native plants and the health of the ecosystems they inhabit (Burgess et al 2017;Hultberg et al 2020;Wan et al 2019). However, the mechanisms driving dieback can be complicated and could result from disease (e.g., soil pathogens or pests) (Grünwald et al 2012), disturbances (e.g., pollution, development) (Mueller-Dombois 1988;Scarlett et al 2013), or other abiotic factors (e.g., soil composition, climate warming, drought), many of which often interact in the progression of dieback (Fleischmann et al 2010;Sangüesa-Barreda et al 2015;Sapsford et al 2021).…”