Infection by pathogenic Phytophthora speInfection by pathogenic Phytophthora species

Infection by pathogenic Phytophthora species

Infection with pathogenic Phytophthora species is generally understood to be one of the greatest threats to the Wollemi Pine. Phytophthora is a genus of water mould, spread primarily by contaminated soil, plant material or water and commonly infecting the roots of susceptible plants, causing dieback and death (DoEE 2018). Since initial research showed severe impacts of P. cinnamomi on seedlings under laboratory conditions (Bullock et al. 2000) and the discovery of P. cinnamomi and P. multivora in Stand 1 in 2005 (Salleh 2005) and 2015 (Puno et al. 2015), respectively, significant effort has been invested in preventing the introduction and spread of soil-borne pathogens within and between the wild stands (such as, through the use of the site hygiene policy), and in the treatment of P. cinnamomi at Stand 1. The effects of infection by Phytophthora spp. can vary through time, and among individuals and may vary with climate, as additional stressors may increase the effects of the infection (Davison 2011).

Research has been undertaken on cultivated Wollemi Pine plants to develop treatment methods to mitigate the impacts of pathogenic Phytophthora. Laboratory and greenhouse experiments have found that painting phosphonate onto the bark of mature Wollemi Pines can reduce the impacts of P. cinnamomi (Liew & Phelan, unpubl. data). While these results are promising, they have important limitations: primarily that the experimental work was conducted on only 20 trees, and that these trees, while the largest available in the ex situ collection, were only 22–24 years old. As such they were relatively young and small compared with most trees in the wild population. Results showed that the technique is effective and provides protection to Wollemi Pine up to 55 weeks or more (E. Liew, pers. comm). However, this estimate could be refined for Wollemi Pine of different sizes by further testing.

Since the previous recovery plan was published, another species of pathogenic Phytophthora has been detected in Stand 1: P. multivora (Puno et al. 2015). No pathogenic Phytophthora species have been detected in soil samples from the other stands (E. Liew, pers. comm.); however, new diagnostic developments which allow better detection and differentiation of Phytophthora species are yet to be used on soil samples taken from the wild stands (B. Summerell, pers. comm.).