Does Hymenoscyphus fraxineus endophytically colonized Fraxinus mandshurica?

Does Hymenoscyphus fraxineus endophytically colonized Fraxinus mandshurica?

Arisa Shigemori1*, Izumi Okane2, Yutaka Tamai3 and Yuichi Yamaoka2

1Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan

2Institute of Life and Environmental Sciences, University of Tsukuba, Japan

3 Research Faculty of Agriculture, Hokkaido University, Japan

*Email: s2221017@s.tsukuba.ac.jp

Hymenoscyphus fraxineus (Helotiales) is an invasive pathogen causing “ash dieback” in Fraxinus excelsior in Europe. In the East Asia where is considered as the local origin of this fungus, one of the host plants is Fraxinus mandshurica, showing no dieback symptom. H. fraxineus has been known to infect the leaves of this plant and to endophytically colonize the leaves until defoliation. However, mycelial extension into the stem was detected after inoculation to the rachis in our DNA assay. This suggests that further investigation is required to clarify the lifestyle of this fungus. This study aimed to reveal the lifestyle of H. fraxineus in F. mandshurica by pinpointing the habitat of this fungus in the plant tissues. We collected both long and short annual shoot from F. mandshurica growing at Hokkaido University, Sapporo, Japan. To investigate whether this fungus inhabits buds, 69 buds of the long shoot and 206 buds of the short shoot were examined. Total DNA was extracted from these buds, followed by PCR with the specific primers to H. fraxineus. As a result, the fungal DNA was detected in 30.4% of the long shoot’ buds and in 63.6% of the short shoot’ buds. The fungal DNA was also detected from those twigs examined in the fungal DNA detection test for the buds. Consequently, it is suggested that H. fraxineus found in leaves originates from both ascospore infections and mycelia already existing in buds or twigs in the previous year or more years ago.