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

Root formation problems (3); withered shoot growth (4); vascular tissue problems (5). VIRUS AND VIRUS-LIKE DISEASES Fleck and enation 4.6

Fleck According to the literature (Bovey et al ., 1980; Marais, 1981; Ferreira & Venter, 1996; Constable & Rodoni, 2011) fleck – also generally known as marbrure – probably occurs throughout the world. Against the background that fleck displays a latent presence in material from scion and most rootstock cultivars, the expression of visually detectable, characteristic traits associated with the disease is inhibited, which obviously impacts negatively on the correct identification procedures. Typical visually detectable abnormalities associated with fleck are best exposed by using Vitis rupestris and specifically du Lot (St. George) as indicator cultivar. In this instance chlorotic, transparent vein interruptions are induced on the finer leaf veins of the third order especially – while leaf edges may also curl upwards and the lamina may become slightly wrinkled (Photo 249). Although fleck is classified as a graft transmissible virus disease, there is surprisingly little in the literature regarding the effect thereof on the general performance of the grapevine and the visual appearance of infected grapevines – especially when it occurs independently. In most instances, however, there is reference to the incidence of delayed bud burst, impaired vigour, stunted growth in young grapevines and the possible occurrence of affinity complications. Although recent research (Santini et al ., 2011) has reported on a change in the pathway of normal anthocyanin synthesis in infected Nebbiolo grapevines, this was in respect of cases where fleck occurred in combination with fanleaf. Taking all of the above into account, one may argue that the world-wide distribution of fleck can probably be ascribed to the latent occurrence thereof in Vitis vinifera cultivars (as well as numerous scion and rootstock hybrids) – thereby paving the way for undisturbed/undetected distribution of associated virus(es) by means of plant material. Enation Just like fleck, enation probably also occurs throughout the world (Winkler et al ., 1974; Marais, 1981) – in which case the occurrence thereof is associated with delayed bud burst and shoot growth, and the incidence of a witche’s broom format in young shoots, as well as in adult grapevines (Photos 250 - 253). In view of the fact that shoot growth usually normalises as the growing season progresses, but especially due to the inconsistent occurrence of characteristic, visually detectable abnormalities from one year to the next on the same grapevines, concrete identification procedures are hugely compromised. Typical of enation (where it occurs on its own) is the appearance of straight or curvy growths – which differ in length – underneath the leaves and parallel to the main veins, while smaller growths may even develop between the veins (Photos 254 & 255). Leaves displaying such growths are usually seriously deformed and may in some instances be

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