P-116 - Colonization by the endophytic fungus Phyllosticta fallopiae combined with the element Si promotes the growth of Dendrobium nobile

Endophytic fungi can promote plant growth and development, particularly of Orchidaceae species. Previously, we found that the endophytic fungus Phyllosticta fallopiae DN14 significantly promoted growth of its host plant D. nobile, an important herb in Chinese traditional medicine. Phyllosticta was positively correlated with fresh weight of D. nobile and with Si content of the epiphytic matrix. Here, we co-cultured D. nobile with P. fallopiae DN14 in 1/2 MS medium with and without various concentrations of Si to investigate the effects of DN14 and Si on plant fresh weight, as well as the underlying mechanisms. The combination of DN14 and Si promoted the lignification of D. nobile roots, stems, and leaves and markedly increased the thickening of xylem cell walls. Co-culture with DN14 increased transport of Si from roots to stems and from stems to leaves. The enhancement of D. nobile growth by DN14 and Si may involve upregulation of plant hormone-related genes (AUX/IAA and MYC) and lignin biosynthesis genes (HCT, PAL1, and PAL2). Insoluble Si promoted the growth of DN14, perhaps through downregulation of genes (e.g., FBP, MPI, RPIAD) related to carbohydrate metabolism, and DN14 in turn promoted the transformation of insoluble Si into soluble Si for plant uptake. These findings demonstrate that endophytic fungi and Si can improve the growth of D. nobile and therefore show promise as organic amendments for commercial cultivation.