We investigated seasonal changes in the discharge of basidiospores, presumed to be the primary inoculum of the causal fungus of Japanese pear dwarf, Fomitiporia sp. From 2008 to 2011, 8 fruit bodies were examined in field conditions. Basidiospores were captured on glass slides coated with glycerin jelly that were placed directly below each fruit body. During these 4 years, basidiospore discharge was intermittent, but started between May 31 and July 7 during the rainy season each year and ended between November 10 and November 21. Ambient temperature at each period was 17.0–24.5°C and 12.1–14.1°C, respectively. In contrast, few basidiospores were captured between December and May. Therefore, we regarded June to November as the discharge period. During this time, the period of discharge was interrupted when there was continuing low rainfall in the summer. In 2011, basidiospore discharge was artificially made consistent by spraying water on fruit bodies at arbitrary intervals during the summer. In laboratory experiments, basidiospores were discharged at temperatures between 20 and 30°C, but not at 10, 15 and 35°C. Under continuous dry conditions, basidiospore discharge was interrupted. Therefore, temperatures and rainfall influence basidiospore formation and subsequent discharge.
In 2007, black spots that appeared on the surface of the rhizomes of ginger (Zingiber officinale Rosc.) during storage caused serious losses in Kochi Prefecture, Japan. Most of the black spots formed at the joints of the rhizomes. A fungus was frequently isolated from the symptomatic rhizomes. The isolate caused the same symptoms on artificially inoculated ginger rhizomes and was reisolated. The fungus formed white stellate colonies with a greenish black spore mass on PDA. Mycelia grew on PDA from 10°C to 35°C with maximum growth at 30°C. Sporangia were fusiform, monocellular, and 7.5–5.0×2.0–3.0 (average 6.4×2.5) µm. The morphology of the fungus agreed with that of Myrothecium verrucaria (Albertini et Schweinitz) Ditmar. The nucleotide sequence of the r-DNA ITS regions agreed well with those of M. verrucaria. In conclusion, the isolate was identified as M. verrucaria. This is the first report of a disease of ginger caused by M. verrucaria, and we propose to designate the disease as myrothecium rhizome spot of ginger.