The effect of grape berry growth stage on germination of Botrytis cinerea in New Zealand

The presence and germination rate of Botrytis cinerea conidia on ‘Sauvignon blanc’ grape berries from Pukekohe, New Zealand, was determined over the 2010–11 and 2011–12 growing seasons by means of inoculated berries. Conidia on the inoculated berries were able to germinate and enter the grape berries at any time during the season, albeit at low rates during the early season. In both years, the proportion of germinated conidia increased with berry age/growth stage. Microscopic examinations revealed that B. cinerea conidia germinated on the grape berry surface and hyphae entered the berries directly either between adjoining cells, by penetrating directly through the cell wall, or via appressoria. Penetration of the grape berry surface was highly variable, with some germ tubes penetrating immediately beneath the conidium and others having extended germ tubes. While most germinated conidia appeared to penetrate the berry, a proportion were seen to germinate to form spermatia (phialomicroconidia). Conidial anastomosis (two conidia connected by a short germ tube) was seen on the surface of some berries.