Differential inhibition of bark endophytes and a wood-decay fungus by inner bark of Sorbus commixta.

The endophytic mycoflora of the bark tissue of Sorbus commixta sampled from Hokkaido, Japan was investigated. Bark pieces were surface-sterilized and placed on potato dextrose agar to extract template DNA from the fungi. Twenty-one operational taxonomic units (OTUs) were isolated from whole and outer bark segments, with colonization frequencies of 20% and 43%, respectively. The fungal composition included 20% OTUs of Pezicula sporulosa and Xylaria spp. in the whole bark, 43% OTUs of Phaemoniella spp., and 24% OTUs of Helminthosporium spp. in the outer bark. Endophytic fungi were not detected in the inner bark segments on the agar. In addition, we examined the antifungal activity (AFA) of S. commixta inner bark against Trametes versicolor and endophytic fungi, including P. sporulosa and Diaporthe spp. We found that the inner bark exhibited selective AFA against endophytic fungi; while inhibition was significant for some, it was lower than the complete inhibition observed against T. versicolor. In conclusion, S. commixta provides a habitat for endophytic fungi in the outer bark, but little or no habitat in the inner bark, likely due to the selective pressure of hydrogen cyanide from cyanogenic glycosides in the inner bark.