A Guide to Grapevine Abnormalities in South Africa - P.G. GOUSSARD

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VIRUS AND VIRUS-LIKE DISEASES

T he appearance of and adverse effects caused by harmful virus and virus-like diseases in infected vines, are a well-known phenomenon in the SA wine industry – whereby a systematic decrease in the quality and quantity of yield is induced in infected vines nearly without exception, with an associated shortened life expectancy. Against the background that in SA a particularly high premium is placed on plant improvement to ensure that only the best material of high phytosanitary quality is planted, it can be reasoned that the still ongoing incidence of virus-associated diseases can be ascribed to a variety of factors/aspects by which, among others, dectection, transmission, spread and reinfection are controlled/regulated. In this connection leading research was undertaken by die Departments of Genetics and Conservation Ecology & Entomology (Stellenbosch University), as well as by ARC Infruitec- Nietvoorbij (Stellenbosch) and the ARC Research Institute for Plant Protection (Pretoria) with the purpose of unravelling varous overarching aspects involved with the grapevine virus complex. Arising from this research various informative and industry applicable findings have already appeared in publication format over time, in which, among others, specific guidelines regarding the control and management of these diseases could be stipulated (Carstens, 2001; Pietersen, 2004/5, 2010; Addison et al., 2011; Coetzee & Burger, 2011; Goszczynski, 2011 and others). Unlike fungal and bacterial diseases, specific abnormalities representative of virus-associated diseases are not associated with local damage and visually observable lesions in or on related organs or organ surfaces, but in infected vines are externally mostly typical of specific organ malformation/distortion – which especially in the case of leaves occurs in conjunction with irregular and unseasonal colour changes according to specific patterns. Associated with this, infected vines are nearly without exception associated with among others smaller root systems, delayed/irregular bud burst, lower reserve levels, stunted shoot growth, smaller leaves, smaller and malformed bunches as well as delayed and

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