Abstract
Behavior of Zygophiala jamaicensis Mason on grape berries (Vitis vinifera L. cv. ‘Muscut of Alexandria’ and cv. ‘Neo Muscut’) was investigated by optical microscopy. On the surface of berries, a pair of two-celled conidia were usually found to attach to bloom. The evanescence of bloom occurred around ungerminated conidia, being 5-15μm wide. A germ tube usually emerged from each cell of conidium. Bloom along germ tubes and hyphae evanesced probably by a degenerating enzyme(s) secreted from them. The width of bloom-evanescing zone increased with growth of hyphae. The evanescing zone formed by paired conidia fused with that by other neighbouring conidia, forming a visible symptom area. Conidia produced on the bloom-evanescing zone seemed to be detached soon after produced. At a later stage of infection, superficial hyphae on the bloom-evanescing zone formed mycelial networks and a great number of thick, dark-colored hyphae gathered, finally to form a black microsclerotium-like structure on the berry surface. Observation of sections of paraffin-embedded specimens revealed that this structure developed on the cuticular surface and that any fungal structures were not found in fruit tissues including epidermis. These observations suggested that Z. jamaicensis could be an ectoparasite which lives on bloom on grape berries. The visible symptom was perhaps ascribed to action of enzyme(s) secreted by this fungus.
