Investigation of Trichoderma species colonization of nursery grapevines for improved management of black foot disease.

Background: Black foot disease (BFD) is one of the main fungal diseases associated with young grapevine decline. Trichoderma holds the potential to be used as biocontrol agent against this disease, though variable success of colonization were found when applied to nursery vines in previous studies. Therefore, field experiments were established to evaluate different methods of application of Trichoderma atroviride, and to evaluate the efficacy of different commercial Trichoderma products on BFD in nursery vines post callusing over two seasons.

Results: Only in one season of the trial evaluating different products did all of the Trichoderma treatments significantly lower the black foot infections in the rootstock bases of the vines (mean black foot pathogen incidence of 1.00 to 2.50% in Trichoderma treated vines versus 6.50% in the untreated control). When comparing tissue parts, the base of the vine and collar roots had significantly higher Trichoderma colonization than the middle and root tip parts. Significantly less BFD pathogens were isolated from the base in comparison to the roots. These colonization trends were found for both field trials over both seasons. The different application methods showed that dipping of basal ends in the dry formulation followed by monthly soil drenches consistently gave higher colonization [mean Trichoderma incidence in the bases were 39.20% (2016/2017) and 28.00% (2017/2018)], while the 1 h soak of the bases of vines was not effective [mean Trichoderma incidence in the bases were 8.80% (2016/2017) and 4.00% (2017/2018)] and did not differ from the untreated control.

Conclusion: Even though Trichoderma spp. were not sufficient to prevent infections by BFD pathogens, a certain degree of protection was obtained in the basal ends, which may contribute to longevity of the vines once planted in the vineyard.