Manipulating rainfall to study symptom expression of <i>Botrytis cinerea</i> infection in wine grapes
Botrytis cinerea infection of wine grapes can result in a variety of symptoms. The most common symptom is botrytis bunch rot (BBR), where infected berries rot and shrivel, and eventually produce fungal sporulation. Another symptom is slip skin, where the skins of infected ripe berries slide easily from the pulp. It is hypothesised that a reduction in osmotic potential in grape berries due to late-season rainfall leads to slip skin symptom development. Hyphal growth of B. cinerea on osmotically adjusted agar was inhibited at osmotic potentials associated with near-ripe berries. Vine sheltering was used in a research vineyard to manipulate rainfall artificially and to alter berry sugar content in Vitis vinifera Sauvignon blanc vines, with the aim of increasing osmotic potential and altering symptom expression. Both BBR and slip skin symptoms were affected by the various sheltering conditions, with sheltered vines having lower BBR and higher slip skin at harvest.