Pathogenicity of Phaeoacremonium aleophilum and Phaeomoniella chlamydospora on grape berries in California

Injured and non-injured grape berries were inoculated with spore suspension of Phaeomoniella chlamydospora or Phaeoacremonium aleophilum under field (intact berries) and laboratory (detached berries) conditions. In one test, berries were injured by pricking the skin with a syringe needle to a depth of approximately 1.5 mm. Brown to purple lesions appeared 5 to 7 days after inoculation in both the injured intact and detached berries. Lesions on these berries were larger when inoculated earlier in the season indicating that young, immature berries are more susceptible to infection than mature berries. In another test, berries were injured by rubbing the skin with carborundum dust using a cotton-tipped applicator. Esca-like lesions developed in 4 to 5 days after inoculation of detached but not intact berries. Occasional infection of non-injured berries occurred which appeared as small dots to pin-head size lesions around the lenticels. Scanning electron microscopy observations of these lesions showed abundant hyphal growth on the surface with apparent penetration through lenticels; however, fungal structures were not detected with certainty beneath the lenticels or intact cuticle. In both tests, the fungi were re-isolated from the advancing margin of the lesions.