Study on the Diversity and Differences of Mycorrhizal Fungi in Dendrobium huoshanense
Dendrobium huoshanense C. Z. Tang et S. J. Cheng, derived from the Orchidaceae genus, is a perennial herbaceous plant that has the effects of enhancing human immunity, antioxidation, repairing liver damage, and preventing the occurrence of cardiovascular diseases. Huoshan Dendrobium not only has great health and medical value, but also has a long history of consumption; In recent years, with more and more people paying attention to health products, their market demand has been continuously increasing. Huoshan Dendrobium is often used as medicine when it is three years old, and the quality of medicinal materials varies among different growth years of Huoshan Dendrobium. The growth form of Dendrobium plants is axial growth. When the main axis reaches a certain stage of growth, it stops growing and begins to produce lateral buds to form a new axis. After reaching a certain stage, lateral buds continue to grow on the new axis and form a new axis, and the plant continues to grow in this cycle. According to the germination time, Dendrobium huoshanense is divided into three-year stems (Ⅲ Y3), two-year stems (Ⅲ Y2), and one-year stems (Ⅲ Y1), corresponding to roots Ⅲ R3, Ⅲ R2, and Ⅲ R1, respectively; Similarly, two-year-old Dendrobium huoshanense can be divided into one-year stems (IIY1) and two-year stems (IIY2), corresponding to roots IIR1 and IIR2, respectively. One year old Dendrobium huoshanense is IY1, corresponding to root IR1. Research has found that the impact of microorganisms on orchids is not only related to seed germination, but also promotes growth, development, and component accumulation.
So far, research on the mycorrhizal fungi of Dendrobium officinale has generally been conducted using traditional culture and isolation methods. The reported genera include Rhizoctonia and Alternaria of Deuteromycota, Chaetomium, Xylaria, Colletotrichum, Fusarium, Tulasnella, Mycena, Sebacina, and Ceramicutes of Ascomycota. Genus Ceratobasidium, etc. Inoculating mycorrhizal fungi onto Dendrobium plants not only promotes plant growth, but also has varying degrees of drought and disease resistance, as well as promoting the accumulation of dendrobine and polysaccharides. Although there have been many studies on endophytic fungi in Dendrobium plants using traditional cultivation and isolation methods in recent years, 99% of microorganisms cannot be isolated due to the high randomness and blindness of microbial cultivation. Currently, research on mycorrhizal fungi in annual Dendrobium huoshanense has not been reported. This article uses high-throughput sequencing technology to study three types of annual mycorrhizal fungi of Dendrobium huoshanense, with the aim of systematically understanding their community diversity, differences, and structural composition, and providing a basis for guiding the rational harvesting and application of Dendrobium huoshanense.

Plant root microbiota can not only promote chemical composition synthesis by regulating gene expression, but also increase the accumulation of secondary metabolites. In recent years, there has been widespread research on the root microbiota of Dendrobium plants, such as the specificity of mycorrhizal fungi in Dendrobium plants and their relationship with host plant phylogenetics. Studies have found that Ascomycota and Basidiomycota fungi are widely distributed in the roots of Dendrobium officinale, a plant in the Dendrobium genus. Due to the limitations of microbial cultivation methods in studying endophytic fungi, this study used high-throughput sequencing technology to discover that the endophytic fungi in the roots of Dendrobium huoshanense are abundant and diverse. Ascomycota and Basidiomycota are the main fungal phyla of endophytic fungi in the roots of Dendrobium huoshanense. Ⅰ R1, Ⅱ R1, and Ⅲ R1 have their own dominant fungi, which is consistent with the dominant position of Ascomycota and Basidiomycota in medicinal plants such as Salvia miltiorrhiza and Dendrobium. Through Alpha diversity analysis, it was found that there were no significant differences in species richness or community diversity among the three groups of samples. However, LEfSe conducted an analysis of the differences in endophytic fungal communities between groups and found that there were significant differences in three families between the IR1 group and the other two groups, with the highest abundance in this group; There are 5 families in Group IIR1 that exhibit significant abundance differences compared to the other two groups; There are four families in Group IIIR1 that exhibit significant abundance differences compared to the other two groups.
Previous studies have shown that the mycorrhizal endophytic true 1898 natural product research and development of traditional Chinese medicine Atractylodes macrocephala in summer has higher fungal diversity than in spring and autumn. This study also investigated the endophytic fungi in the roots of Dendrobium huoshanense in different seasons. It was found that in May, the abundance of Ascomycota was the highest and the abundance of Basidiomycota was the lowest in the roots of Dendrobium huoshanense. In September, the abundance of Basidiomycota was the highest and the abundance of Ascomycota was the lowest, indicating that season may be an important factor affecting the community structure of mycorrhizal fungi in Dendrobium huoshanense. In future research, it is planned to combine the rhizosphere microorganisms of Dendrobium officinale with chemical components, focusing on the influence of root microorganisms on the effective components of Dendrobium huoshanense, in order to provide scientific basis for improving the quality of Dendrobium huoshanense and developing microbial fertilizers.
In summary, this study applied Illumina MiSeq high-throughput sequencing method to sequence the ITS1-2 region of mycorrhizal fungi in Dendrobium huoshanense, obtaining 898663 ITS rRNA sequences and 1928 OTUs. Based on OTU clustering analysis, 9 phyla, 30 classes, 71 orders, 149 families, and 244 genera were identified. Among them, Ascomycota, Basidiomycota, and Mucomycota were the main fungal phyla of endophytic fungi in the roots of Dendrobium huoshanense, with Ascomycota having the highest abundance and Basidiomycota having the lowest abundance in May; LEfSe analysis found that there are 44 distinct taxonomic branches of mycorrhizal fungi in three types of annual Dendrobium huoshanense (a=0.01, LDA score≥2. 0) ; Through Alpha diversity analysis, it was found that in terms of species composition and diversity, the order was IIR1>IIIR1>IIR1. However, the Alpha diversity evaluation boxplot showed no significant differences among the three groups.