The effect of bagging branches on levels of endophytic fungal infection in Japanese beech leaves

SummaryThe species composition of the endophytic mycobiota in leaves of Japanese beech trees (Fagus crenata) and the sources for leaf infections were studied in a forest reserve situated in central eastern Honshu, Japan. To clarify the mechanism of infection of leaves, half of the branches were covered with polyethylene bags and species composition and levels of endophytic fungal infection were then compared with those of unbagged controls. Isolations were carried out from the leaves, petioles, and current‐year twigs of both, bagged and unbagged branches. Additionally, species composition was detected in overwintered terminal buds of beech trees and in the leaves of potted seedlings that had been placed in the field in different seasons. The species assemblage of the unbagged leaves, petioles, and current‐year twigs was dominated byMycosphaerella buna,Ascochyta fagi,Periconiellasp., andTritirachiumsp. Other frequently recovered species wereXylariasp.,Phomopsissp., andTubakia dryina.Mycosphaerella bunaandA. fagiwere never isolated from leaves on bagged branches.A. fagiwas, however, detected on both bagged and unbagged petioles and current‐year twigs at comparatively low isolation frequencies. The detection ofPericoniellasp. on all occasions in both bagged and unbagged leaves was a characteristic feature that differs from those of the other three dominant endophytic fungi. The fungus was also detected without significant differences in bagged and unbagged petioles and current‐year twigs on most sampling dates. Furthermore,Periconiellasp. was isolated from immature twigs inside the bud scales.Tritirachiumsp. was frequently detected in unbagged leaves and petioles and in both bagged and unbagged current‐year twigs, and rarely in bagged leaves and petioles, but was never recovered from terminal buds. The results of the potted seedling experiments revealed that all four dominant species had airborne inocula. The infection of leaves byM. bunaoccurs exclusively by airborne propagules, i.e. ascospores in spring and conidia in autumn. InPericoniellasp. hyphal growth of the fungus from immature twigs inside the buds into the leaf tissues was suggested in addition to infection by airborne inocula.Tritirachiumsp. hyphae were suggested to grow from previous‐ to current‐year twigs.Ascochyta fagiwas present in the outermost scales of overwintered terminal buds, but no systemic growth of the fungus into the petioles and current‐year twigs was observed. Our technique of covering the branches before new leaves unfolded was effective in preventing infection by airborne inocula of endophytic fungi.