Use of root endophytic Trichoderma for Psa-V control in New Zealand kiwifruit

Abstract

The kiwifruit disease Pseudomonas syringae pv. actinidiae (Psa-V) was first identified in New Zealand in 2010 and currently affects over 85% of the country’s kiwifruit orchard area. Our research focused on the use of Trichoderma isolates as a biological control option of Psa-V. These root endophytic fungi have the potential to colonise root surfaces and penetrate roots, and to limit the damaging effects of pathogens by releasing metabolic compounds, incl. antibiotics, inducing systemic resistance, and improving general plant health. Root colonisation with Trichoderma can also enhance plant growth, crop productivity, nutrient uptake and resistance to abiotic stresses. To identify promising isolates for the control of Psa-V, root endophytic Trichoderma were isolated from healthy kiwifruit vines and other plant species in areas with high Psa-V incidence and assessed by inoculating young kiwifruit seedlings under environmentally controlled conditions with different isolates as mixtures or single isolates. 8 to 10 weeks after inoculation, seedlings were challenged with Psa-V by stab inoculation and disease progression and seedling survival were assessed over 4 weeks. To assess the effect of Trichoderma inoculation on roots of established plants with an existing microflora Trichoderma were re-isolated from the roots of orchard vines that had or had not received Trichoderma. Several promising mixtures and single isolates were identified as reducing Psa-V symptoms and increasing plant survivability and our results indicate that a single Trichoderma inoculation early during plant development has a significant effect on kiwifruit plant health and survival. Field trials in Psa-V infected kiwifruit orchards using container-grown kiwifruit also confirmed the efficacy of the best treatments alone and in combination with a plant elicitor and other microorganisms to reduce Psa-V symptoms on different kiwifruit cultivars. Re-isolating Trichoderma from orchard vines showed significantly higher numbers of Trichoderma in the roots of the treated compared to the untreated plants. The results suggest that inoculation of older orchard vines facilitates the establishment of a strong root endophytic Trichoderma community that may improve plant health and thus contribute to the control of Psa-V on kiwifruit.