Abstract
A new symptom of grape (Vitis vinifera L. cv. ‘Muscut of Alexandria’ and cv. ‘Glos Colman’), the evanescence of a bloom which normally covers on the skin of berries, has been prevailing in greenhouses in Okayama Prefecture, Japan, since several years ago. No necrotic lesion nor rot of berries was seen. Similar symptom has been also found on Japanese persimmon and apple fruits in Okayama. The evenescence of the bloom on affected berries is visible to the naked eyes in accordance with the extention of subhyaline, superficial creeping mycelium which tends to form mycelial networks on berries. After a later stage of the symptom development, black microsclerotia-like bodies are produced in abundance, which give to berries typical flyspeck symptom on them. Conidial structures, spiral tubular conidiophores and gourd-shaped conidia, are formed on the creeping mycelium, particularly around the microsclerotia-like bodies. Based on the morphological characteristics of the causal pathogens on grapevine, it was identified as Zygophiala jamaicensis Mason apud Martyn, a hyphomycete fungus. The causal fungus of flyspeck of Japanese persimmon and apple was also found conspecific with this species. On the diseased fruits concerned, however, there was no evidence for Leptothyrium pomi (anamorphic state of Schizothyrium pomi) which was thought to be the causal agent of flyspeck of various kinds of fruits. Two types of clony were segregated on the potato sucrose agar media. One (type A) is of fast growing type which produces both microsclerotia-like bodies and conidial structure in abundance. The other (type B) is of slow growing type which also produces the conidial structures well, but produces few microsclerotia-like bodies. The fungus can grow at a range of temperature at 6-28C and of pH 3-11. The optimum temperature for growth was at 20-25C. Inoculation tests by selected isolates from grapevine, Japanese persimmon and apple on non-injured fruits of grapevines, Japanese persimmons and apples revealed that these isolates are virulent to these fruits.
