Fungi of grapes

Abstract

Grapevine can be attacked by a number of fungi and fungus-like organisms which affect the berries and cause loss of quality and influence the taste of the wine. Due to attack by pathogens, the infected plant tissue is destroyed and necrotization occurs. When large areas of the canopy are affected by grapevine diseases, the assimilation capacity of the vine is reduced, and as a result the berry quality decreases. Aside from leaves, most grapevine pathogens also infect inflorescences, clusters and berries so that the yield can be reduced. Berry infections result in decay of fruit tissue; however specific effects on berry quality depend on the ripening stage at which the infection occurs. Some pathogens directly destroy the fruit tissue enzymatically; others impede ripening, and a number of fungi produce off flavours or mycotoxins. Grapevine diseases can spread rapidly under favourable conditions and cause more or less severe epidemics. To avoid loss of quality and yield, the pathogens have to be controlled by appropriated culture techniques and targeted application of fungicides. Besides the pathogenic fungi causing grapevine diseases, berries are also colonized by ubiquitous epiphytic fungi which use sugar and amino acids leaking out of berries as nutrient source. In general grapevine pathogens can be subdivided into main pathogens of high economical importance which are pre-dominant, like downy mildew (Plasmopara viticola), powdery mildew (Erysiphe necator) and bunch rot (Botrytis cinerea) and those which occur only locally or temporarily. Moreover other important grapevine diseases are caused by wood decaying fungi which pre-dominantly attack the trunk and canes (Fischer and Kassemeyer 2003). In the present chapter such fungi and oomycetes are regarded which colonize grapevine berries and consequently may influence the must and wine. All fungi reported to colonize grapevine berries are listed in Table 4.1; however some of them can be regarded as harmless epiphytes, others actually as antagonists of pathogenic fungi, e.g. Trichoderma and Ulocladium (Schoene and Köhl 1999; Li et al. 2003). Some of the fungi produce mycotoxins (Table 4.2; cf. Chap. 7) which are more or less human toxic, and some may release compounds which are toxic to yeasts. In addition numerous fungi colonizing the berry surface during different stage of berry development and ripening have been identified (Table 4.3).