The susceptibility of seven threatened species to Phytophthora gregata and the aetiology of the disease caused by it

Abstract

Collar rot associated with the pathogen Phytophthora gregata T. Jung, M.J.C.Stukely & T.Burgess was recently observed on a subalpine wetland shrub, Pimelea bracteata Threlfall, in Kosciuszko National Park, New South Wales. The symptomatic collars of infected plants in the field may mean that P. gregata infects via the collar rather than through roots, as many other Phytophthora species do. In the glasshouse, we tested the susceptibility of seven threatened wetland species to P. gregata. Flooding and stem wound inoculations were applied as treatments. Based on symptoms and reisolations, we found that Boronia deanei ssp. acutifolia Duretto, Correa baeuerlenii F.Muell, Pultenaea parrisiae J.D.Briggs & Crisp and Pimelea bracteata were susceptible to P. gregata. These species were infected following both flood and stem inoculation, and all but C. baeuerlenii displayed very poor health under both treatments; stem wound inoculated C. baeuerlenii plants tended to be less affected than root inoculated plants. The pathogen could not be reisolated from the roots and collars of inoculated plants of Callistemon purpurascens S.M.Douglas & S.David, Grevillea acanthifolia ssp. paludosa Makinson & Albr., and Pultenaea aristata Sieber ex DC. This is the first test of the susceptibility of eastern Australian native plants to P. gregata and the first to investigate the aetiology of the disease caused by this emerging threat. Given the growing body of evidence of the effects of a range of Phytophthora species on native plants, we suggest that the Key Threatening Process listing be broadened to include all destructive Phytophthora species.