Growth Responses of Kauri (Agathis australis) To Inoculations with Different Mycorrhizae

Abstract

Kauri (Agathis australis) were once an economic commodity, until resources declined. Kauri have been protected since 1973 in NZ legislation. Recently, Phytophthora agathidicida has become a threat to kauri. There is a need to support kauri health and survival. A potential solution is facilitating the use of arbuscular mycorrhizal fungi (AMF) to enhance growth and resilience of kauri to disease. AMF are known to increase nutrient uptake, increase survival and protect against pathogens within host plants. This study attempted to artificially inoculate AMF into the roots of kauri with a range of techniques, most of which have not been attempted before with kauri. There were two trials; (1) A germination trial was carried out with kauri seeds sown into AMF inoculated soils. Germination rate was significantly reduced in kauri duff treatments but not in other treatments including the control. Emerged seedlings had their growth and survival monitored. Duff treatment seedlings had the least growth and were more likely to die within two months of germination. ITS and 18S rRNA genetic sequencing results show only one instance of potential AMF species which was observed in the duff treatment. It is unlikely any benefits of AMF occurred because of high mortality of the duff seedlings. (2) A trial was also carried out attempting to stimulate established kauri seedling growth by inoculating seedlings with mycorrhizae. Kauri duff treatment seedlings were all negatively affected in growth and became moribund during the trial, possibly due to either allelopathy or soil pathogens. Growth of seedlings treated with Mycormax® or in which I attempted to inoculate kauri seedlings from bait plants were not significantly different to the non-AMF control plants. There was high variation within the fungal species communities that colonized the roots of the different treatments. As well, a difference in seedling growth were observed relative to different bait plant types. ITS and 18S rRNA genetic sequencing results showed one potential AMF species in the Mycormax® treatment (Funneliformis mosseae). With non-significant differences in seedling growth, however, it is unlikely any benefits from AMF occurred. Overall, my attempts to inoculate kauri with AMF met with limited success, however insights into the effects of kauri duff and bait plants were made. Future attempts with artificially inoculating kauri with AMF should consider other inoculation techniques, such as; direct spore collection, agar plugs or root deeping.