**Molecular Identification of Endophytic Fungi and Their Pathogenicity Evaluation Against** *Dendrobium nobile* **and** *Dendrobium o*ffi*cinale*

**Surendra Sarsaiya 1,2,**† **, Archana Jain 1,**†**, Qi Jia 2, Xiaokuan Fan 3, Fuxing Shu 2, Zhongwen Chen 2, Qinian Zhou 2, Jingshan Shi 1,\* and Jishuang Chen 1,2,3,\***


Received: 4 November 2019; Accepted: 2 January 2020; Published: 2 January 2020

**Abstract:** *Dendrobium* are tropical orchid plants that host diverse endophytic fungi. The role of these fungi is not currently well understood in *Dendrobium* plants. We morphologically and molecularly identified these fungal endophytes, and created an efficient system for evaluating the pathogenicity and symptoms of endophytic fungi on *Dendrobium nobile* and *Dendrobium o*ffi*cinale* though in vitro co-culturing. ReThe colony morphological traits of *Dendrobium* myco-endophytes (DMEs) were recorded for their identification. Molecular identification revealed the presence of *Colletotrichum tropicicola*, *Fusarium keratoplasticum*, *Fusarium oxysporum*, *Fusarium solani*, and *Trichoderma longibrachiatum*. The pathogenicity results revealed that *T. longibrachiatum* produced the least pathogenic effects against *D. nobile* protocorms. In seedlings, *T. longibrachiatum* showed the least pathogenic effects against *D. o*ffi*cinale* seedlings after seven days. *C. tropicicola* produced highly pathogenic effects against both *Dendrobium* seedlings. The results of histological examination of infected tissues revealed that *F. keratoplasticum* and *T. longibrachiatum* fulfill Koch's postulates for the existence of endophytes inside the living tissues. The DMEs are cross-transmitted inside the host plant cells, playing an important role in plant host development, resistance, and alkaloids stimulation.

**Keywords:** Dendrobium; molecular identification; endophytic fungi; pathogenicity; protocorm; seedling
