Plants, fungi, and freeloaders: Examining endophytic species richness changes over the growing season of Arceuthobium americanum

Arceuthobium americanum, or the lodgepole pine dwarf mistletoe, is a tree parasite in northern Canada. The plant has negatively impacted the lumber industry, causing significant financial losses, particularly in the west. Recently, endophytic fungi have been found in this plant, which have been discovered to function in protecting the plant from surface pathogens. The current study aimed to examine the endophytic fungi in more depth, looking for changes in species richness over the plant’s growing season and determining whether these richness changes differed between males and females. This information could yield a new management strategy, which would involve applying a surface pathogen spray at a time when the endophytic fungal diversity is lower and the plant is presumably more susceptible to pathogens. Using pure culture techniques, endophytic fungi were isolated from surface sterilized A. americanum males and females weekly from the end of April to the beginning of September. Isolated fungi were characterized macroscopically to generate a database of morphologically unique forms that corresponded to individual species. Endophytic fungi that appeared consistently throughout the sampling period were sent to be sequenced by MACROGEN™ sequencing in Korea to determine their identities based on ITS rDNA sequences. Throughout the study period, 47 distinct morphological strains of fungi were isolated. Endophytic fungal species abundance was found to increase throughout the growing season in both males and female A. americanum plants. There was no significant difference in the species richness between males and females, and the two groups shared 87.5% species similarity based on Sørensen’s coefficient of similarity. Sequenced endophytes found in this study came from a diverse array of genera, including Trichoderma, Serpula, Alternaria, and Tremella, which may function as mutualistic symbionts within the plant. Endophytic fungal species richness follows the trend shown by all other plants to date: it increases throughout the growing season in new aerial shoots. Future work should aim to further characterize endophytic communities using metagenomic techniques and comparing endophyte communities of A. americanum to those of the host tree to see if there is crossover between the two organisms.