Screening of Agathis australis endophytes as biological control agents against kauri dieback pathogen Phytophthora agathidicida

Agathis australis (Kauri) is a significant and iconic native tree of Aotearoa, New Zealand. A disease known as kauri-dieback is currently affecting kauri trees. The aetiology of the disease has been associated with Phytophthora agathidicida (PA) which poses severe threat to kauri at individual and population levels. Currently, the only treatment available is the injection of phosphite into the trees. We investigated the potential of fungal endophytes to influence the growth of PA. Seventeen previously isolated endophytic fungi from kauri roots were examined morphologically and the antagonistic effects against the plant pathogen. Five of the 17 fungal endophytes tested demonstrated growth suppression of the pathogen in dual culture. Pezicula sp. partly inhibited the growth of P. agathidicida whilst Coprinellus micaceus and Ilyonectria mors-panacis completely inhibited the growth of the pathogen. Oospores were not observed in the dual culture nor was the P. agathidicida viable when transferred into fresh culture media. This study illustrates that naturally occurring fungal species in kauri roots can suppress the growth of PA. This finding offers a possibility of a biological control for dieback disease in kauri which may contribute to the mitigation of natural disease management and biocontrol of plant diseases without compromising the natural ecosystem.