Effect of Trichoderma atroviride Application on Tea Yield and Its Impact on the Soil Microbiome in a New Zealand Tea Plantation

New Zealand’s only tea (Camellia sinensis) plantation supplies a niche market for organically produced high value tea but faces challenges from climatic conditions and the decision to use only organic production methods. Fungi from the genus Trichoderma have been commercialised in New Zealand and elsewhere as disease-suppressing and plant growth-promoting agents. However, the potential benefits of using Trichoderma as a microbial biostimulant for tea cultivation have not been investigated in New Zealand. The ability of T. atroviride application to stimulate tea plant growth at a tea plantation was investigated over one year of production. The study involved foliar application of the biostimulant either once, twice or three times, one month apart, using 12 g of a commercially formulated spore mixture of four strains of T. atroviride per 5 m2 of experimental plots. Treatment with T. atroviride significantly increased tea yield by between 17% and 28% compared to the control over the harvesting season, but there were no statistically significant yield differences among the number of applications. The foliar applied T. atroviride was not detected in the soil or root samples six months after application, in either a soil metabarcoding analysis or on re-isolation media. This was likely due to the dense tea foliage and ground cover under the tea plants which impeded its movement to the soil. While the specific nature of T. atroviride interaction with perennial crops like tea is not known, in this trial it appeared to have remained on the phyllosphere and provided biostimulation without reaching the soil.