Inoculating Agathis australis with fungal endophytes to test the viability of a potential biological control agent for Phytophthora agathidicida

Abstract

Phytophthora agathidicida is an oomycete pathogen found in the roots of Agathis australis (kauri) trees and has had a detrimental effect on the kauri population in New Zealand. The pathogen is the causal agent of kauri dieback and attempts to control the spread of P. agathidicida have been difficult. Certain fungal endophytes have been proven to have positive effects on host plants by providing protective secondary metabolites as well as competing for nutrients against pathogens. This study aimed to gather preliminary data on two fungal endophytes from the ICMP (International Collection of Microorganisms from Plants) that were originally isolated from healthy mature kauri roots in the Waitakere Ranges in Auckland, New Zealand. Both endophytes demonstrated an antagonistic relationship with P. agathidicida in-vitro on four separate nutrient media. One endophyte was found to be in the class Sordariomycetes and the other in Leotiomycetes. Tissue culture kauri micro-shoots were inoculated with either the Sordariomycetes or Leotiomycetes endophyte and grown both in a laboratory and nursery setting to measure the impacts of each endophyte on kauri host plants. Two inoculation methods were tested for each endophyte and the 'base block method', where the base of the plant is inserted into an endophyte colonised agar block, was found to be successful. Endophytes were found to inhabit within stem material in-vitro and colonisation increased over time. Colonisation from fungal endophytes did not significantly impact the leaf number or leaf necrosis in individual host plants; however, colonisation did cause stunted height in kauri. Each fungal endophyte had the same impact as each other on kauri micro-shoots. Impacts on kauri growth by fungal endophytes in a nursery environment were inconclusive as many other microorganisms had colonised the kauri plant material over time. The results from this study provide evidence to suggest that both fungal endophytes could be considered as potential biological control agents against P. agathidicida. There are currently challenges to testing this theory in field conditions.