The response of sugi ( Cryptomeria japonica D. Don) sapwood to fungal invasion following attack by the sugi bark borer

Abstract

The response of sapwood of the gymnosperm sugi, Cryptomeria japonica, to fungal invasion following attack by the sugi bark borer, Semanotus japonicus, was investigated. Norlignans—agatharesinol, hinokiresinol and sequirin-C—accumulated in the inner intermediate wood which surrounded discoloured sapwood. Hinokiresinol and two unidentified compounds showed inhibitory effects on Fusarium oxysporum, F. solani and Macrophoma sugi, which were isolated from discoloured sapwood, and Cladosporium herbarum. Most of the ray parenchyma cells in the inner intermediate wood were still alive. Spreading of fungal hyphae colonizing discoloured sapwood was inhibited at the boundary of the inner intermediate wood with the discoloured sapwood. Oil droplet-like deposits in tracheid lumina and pits of the inner intermediate wood were found to occlude many tracheids. The deposits contained lipid and phenolic compounds including norlignans such as hinokiresinol. These results suggest that the deposits form a continuous barrier at the margin of discoloured sapwood, in the wood formed prior to the infection, and prevent the fungi from spreading further.