Anatomical and histochemical characteristics of Japanese birch (Tohoku) plantlets infected with the Inonotus obliquus IO-U1 strain

Abstract

Host-pathogen interactions were investigated on a Japanese birch (Betula platyphylla var. japonica, Tohoku) plantlet after infection with a canker-rot fungus, the Inonotus obliquus IO-U1 strain. For a time-course study, intact, wounded, and infected plantlets were collected from 2 h to 30 days after treatment. Notable changes were observed morphologically in the treated portion of wounded and infected plantlets. Phenolics first deposited at the cut margin and subsequently in vessels after 4 h of infection. Their deposition extended to other xylem elements, the cortex, and the pith with an increase in the infection period. Phenolics deposition was extensive at 10 days post-inoculation (dpi), when most of the cells were entirely filled with phenolics. A necrophylactic periderm (NP) was formed at the junction of the original periderm with a layer of 2-4 new phellem cells at 30 dpi. Based on the results obtained, phenolics deposition and NP formation are considered to occur as infection-induced responses in Tohoku birch plantlets infected with I. obliquus IO-U1.