Objective Diplodia tip blight of Mongolian pine is widely distributed in Honghuaerji, Inner Mongolia of northern China, causing severe damage on natural Mongolian pine (Pinus sylvestris var. mongolica). Our study analyzed the diversity and community structure of endophytic fungi in different parts of asymptomatic and symptomatic Mongolian pine infected by Diplodia sapinea, laying a research foundation for the subsequent screening of effective endophytic antagonistic strains and the control of diplodia tip blight.

Method Using culture-based and high-throughput sequencing techniques, the diversity and structure of endophytic fungal communities in different tissues (needles, twigs and phloem) of asymptomatic and symptomatic Mongolian pine were compared and analyzed, and endophytic fungi with significant differences in abundance at twigs were screened.

Result (1) 360 and 233 taxa of endophytic fungi were isolated from symptomatic and asymptomatic Mongolian pine, respectively. D. sapinea was isolated from both asymptomatic and symptomatic Mongolian pine, with the highest isolation rate. In addition, Hormonema sp. had a higher isolation rate on asymptomatic Mongolian pine, but a lower isolation rate on symptomatic Mongolian pine, and it was only isolated from the diseased twigs. (2) The amplicon sequencing results showed that there were no significant differences of α diversity of endophytic fungi between symptomatic and asymptomatic Mongolian pine, but beta diversity, community composition and structure of endophytic fungi were various according to different tissues from symptomatic and asymptomatic Mongolian pine. (3) Linear discriminant analysis effect size (LEfSe) analysis of amplicon revealed that the fungus Diplodia sp. was significantly enriched in the twigs of symptomatic Mongolian pine, while Hormonema sp. was significantly enriched in the twigs of asymptomatic Mongolian pine. (4) Fungal trophic classification confirmed that the relative abundance of saprophytic fungi was highest in all three parts of asymptomatic Mongolian pine, while the relative abundance of plant pathogens in the phloem of symptomatic Mongolian pine was significantly increased.

Conclusion There are no significant differences in the diversity of endophytic fungi between symptomatic and asymptomatic Mongolian pine, but there are significant differences in the community structure of endophytic fungi in different tissues. In the future study, antagonistic experiments will be conducted to evaluate the potential of fungi Hormonema sp. from asymptomatic Mongolian pine as biocontrol agents.