Occurrence of Gray Mold on Current-year Containerized Sugi (Cryptomeria japonica) Seedlings

Abstract

In mid-July 2020, a gray mold outbreak was confirmed in current-year Sugi (Cryptomeria japonica D. Don) seedlings grown in the open field and in the glass room at the containerized seedling production site in western Shimane Prefecture, Japan. The percentage of diseased seedlings in the open field was only 11％, whereas in the humid glass room, it was as high as 38％. BLAST analysis of the nucleotide sequence of the rDNA internal transcribed spacer region revealed that the isolated strain was 100％ homologous to Botrytis cinerea Pers. The strain was inoculated on the branches and leaves of Sugi current-year-old containerized seedlings in late August and late November under 20 ℃, wet, and dark conditions. After 10 days, the outbreak of the disease was investigated. The percentage of diseased seedlings was as high as 94％ in August, but decreased to 0％ in November. The branches and leaves of the seedlings in August (during the growing season) were softer than those in November (during the resting period). It is therefore inferred that the softer nature of the seedlings during the growing season makes them more susceptible to infection by the pathogen.