WINETECH Technical Yearbook 2021

VITICULTURE RESEARCH | JULY 2021

Trichoderma as possible biocontrol agent against black foot disease in grapevine nurseries

WYNAND VAN JAARSVELD 1 , FRANCOIS HALLEEN 2 & LIZÉL MOSTERT 1 : 1 Department of Plant Pathology, Stellenbosch University, Stellenbosch; 2 ARC Infruitec-Nietvoorbij, Stellenbosch KEYWORDS: Biological control, grapevine trunk diseases, Trichoderma-based products, methods of application.

THE AIM OF THIS STUDY was to compare different Trichoderma-based products, as well as different methods of application in large scale nursery trials, in order to improve Trichoderma colonisation and control black foot disease infections. BACKGROUND Black foot disease (BFD) is caused by a pathogen complex that occurs in soils as saprophytes or weak plant pathogens and are present in most grapevine nurseries in South Africa. Infected vines that experience stress can develop BFD symptoms. Typical below ground symptoms of the disease include sunken necrotic root lesions and reduction in root biomass that often result in the formation of a second crown of horizontally growing roots on the upper

level of the rootstock, while the rootstock diameter appears to be thinner. Internal symptoms include black discolouration developing from the base and extending upwards in the rootstock, necrotic lesions and congested xylem vessels that spread from the bark to the compacted pith. Vine decline becomes apparent as stunted growth, shortened internodes, sparse foliage and reduced vigour, as well as small leaves with interveinal chlorosis and necrosis. There are no curative control measures available to eradicate BFD in nurseries or vineyards and, therefore, preventative management is of utmost importance. Various studies have investigated the use of chemical fungicides with little success, due to its inability to penetrate phloem and

xylem tissue, fluctuating levels of sensitivity of BFD pathogens and the shortage of registered products. Hot water treatment (HWT) of dormant nursery vines, a process in which rooted vines are heated to 50°C for 30 minutes, have been considered effective to control BFD, though its effect is short- term and may result in subsequent vine failure if not executed properly or if low quality propagation material is used. The use of Trichoderma species as biological control agents (BCA) offers more sustainable and lasting protection against numerous grapevine trunk diseases and, therefore, the question arose as to whether Trichoder- ma-based products would hold potential in nursery application for improved plant health and management of BFD. In previ-

FIGURE 1. Appl ication of dry product formulation to dampened basal ends of callused graftlings before planting.

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