Virulence of Fungi Isolated from Ambrosia Beetles to Acer amoenum Branches.

In Japan, no association between the ambrosia beetle and their fungal symbionts causing branch dieback or tree mortality on maple, Acer amoenum, has been reported. However, we identified dieback of several branches and numerous holes created by three species of ambrosia beetles, Euwallacea fornicatus, Euwallacea interjectus, and Platypus calamus, on Acer amoenum trees at the University of Tokyo Tanashi Forest, Tokyo Metropolis, Japan, in 2016. The high attack density of the beetles was observed on the weakened trees; however, the contribution of the associated fungi to the branch dieback was still unknown. We isolated fungi carried by these three beetles and inoculated them to Acer amoenum cut main trunks and sapling branches to determine whether the associated fungi caused the branch dieback. Fusarium euwallaceae was isolated from all Euwallacea fornicatus and Euwallacea interjectus, whereas Arthrinium phaeospermum, Raffaelea cyclorhipidia, and Epicoccum nigrum were isolated from P. calamus, with 35, 15, and 5% isolation frequencies, respectively. Inoculation with F. euwallaceae and R. cyclorhipidia induced statistically significantly wider sapwood discoloration (six and four times wider for F. euwallaceae and R. cyclorhipidia, respectively) than the controls, and larger water-conductance loss (2 and 1.7 times larger for F. euwallaceae and R. cyclorhipidia, respectively) than the controls. However, the observed lesions were not large enough to cause discoloration, and symptoms of dieback were not observed, even 13 months after the inoculation. Therefore, we concluded that the virulence of the four investigated fungi to Acer amoenum was very low and that these fungi were likely not the primary cause of the branch dieback.

Quantitative real-time PCR (qPCR)--based tool for detection and quantification of Cordyceps militaris in soil.

A quantitative real-time PCR using a primer pair CM2946F/CM3160R was developed for specific detection and quantification of Cordyceps militaris from soil. Standard curves were obtained for genomic DNA and DNA extracts from autoclaved soil with a certain dose of C. militaris suspension. C. militaris was detected from two forest soil samples out of ten that were collected when fruit bodies of C. militaris were found. This method seemed effective in detection of C. militaris in the soil and useful for rapid and reliable quantification of C. militaris in different ecosystems.