Leaf endophyte community composition and network structures differ between tolerant and susceptible English boxwood

Differential tolerance of English boxwood to boxwood blight has been linked to the ratio of culturable bacterial and fungal dominance in the leaf tissue of representative samples. To further understand how the whole endophyte communities may involve the tolerance of large samples, we extracted DNA from healthy leaf tissue of previously identified 28 tolerant (T), 41 moderately tolerant (M) and 21 susceptible (S) English boxwood plants, then sequenced associated bacterial and fungal amplicons using the Nanopore MinION platform. The endophyte community did not differ in diversity among the T, M, and S plants, but differed in the abundance of bacteria and fungi, particularly between T and S samples. The bacterial genera Brevundimonas and Ammonifex had higher relative abundance in the T and M communities than in the S community which was more dominant by the fungal genera Botrytis, Thermothelomyces and Chaetomiaceae. The same results were obtained when mother and daughter samples in the T community were compared with controls in the S community, suggesting bacteria as a work force in the T community. Co-occurrence network analyses revealed that the T network had more fungal hubs but less complex with more positive connections than the S network, suggesting that the T community was supported by a healthier network. The resistance of English boxwood to blight is likely attributed to bacteria dominance and a synergic community network. This study is foundational to constructing synthetic communities and using whole communities of tolerant plants through vegetative propagation for microbe-modulated immunity.