Comparison of application of root endophytic Trichoderma into established kiwifruit orchards

Abstract

The kiwifruit disease Pseudomonas syringae pv. actinidiae (Psa) was first identified in New Zealand in 2010 and currently affects over 85% of the country’s kiwifruit orchard area. Our research focused on root endophytic Trichoderma as a biological control option for Psa, as these fungi can limit the damaging effects of pathogens through antibiotic metabolites, induce systemic resistance and improve plant health. Promising biocontrol isolates were identified by inoculating kiwifruit with Trichoderma under controlled conditions and in the field before exposing them to Psa. The mixture TriMix-1 emerged as one of the best performing treatments consistently lowering disease incidence and increasing kiwifruit seedling longevity. To assess persistence in kiwifruit roots and determine the best method to apply TriMix-1 into existing orchards, endophytic fungi were re-isolated from kiwifruit roots at two organic NZ kiwifruit orchards following four treatments: Trichoderma root application with (N) and without nutrient solution (T); surface application with vermicompost (V); untreated control (C). While similar numbers of Trichoderma were isolated from the two sites, treatment effects were significant and treatments T, V and N increased Trichoderma counts compared to the untreated control. Inoculation of older orchard vines using a suitable application method facilitates the establishment of a strong root endophytic Trichoderma community that can improve plant health.