First report of flower bud rot of hydrangeas caused by <i>Botrytis cinerea</i> in Japan

Severe flower bud rot was observed in hydrangeas (Hydrangea macrophylla) growing in Shimane Prefecture, Japan. This symptom was observed in potted hydrangeas grown under forcing culture in greenhouses during winter. A gray mold pathogen (Botrytis cinerea) was isolated from rotten buds, and the original rot symptom was reproduced via inoculation with the isolates. The identification of the pathogen was confirmed by morphology and molecular phylogeny. This is the first report of hydrangea flower bud rot caused by B. cinerea in Japan.