Changes in global Orchidaceae disease geographical research trends: recent incidences, distributions, treatment, and challenges

Perspective and challenges of mycorrhizal symbiosis in orchid medicinal plants

The family Orchidaceae is of the most diverse taxon in the plant kingdom, and most of its members are highly valuable herbal medicines. Orchids have a unique mycorrhizal symbiotic relationship with specific fungi for carbohydrate and nutrient supplies in their whole lifecycle. The large-scale cultivation of the medicinal plant Gastodia elata is a successful example of using mycorrhizal symbiotic technology. In this review, we adopted G. elata and Dendrobium officinale as examples to describe the characteristics of orchid mycorrhiza and mycorrhizal benefits for host plants' growth and health (e.g. biotic and abiotic stress and secondary metabolite accumulation). The challenges in applying mycorrhizal technology to the cultivation of orchid medicinal plants in the future were also discussed. This review aims to serve as a theoretical guide for the cultivation of mycorrhizal technology in medicinal orchid plants.

Micropropagation of Guarianthe skinneri (Bateman) Dressler & W. E. Higging in Temporary Immersion Bioreactors

Guarianthe skinneri (Bateman) Dressler & W. E. Higgins is an orchid valued for its ornamental characteristics. However, it is an orchid classified as threatened with extinction due to the illegal extraction from its natural habitat. In addition, its propagation through seed germination is very low, as is the case with most members of the family Orchidaceae. Its asexual propagation through pseudobulb separation is slow and produces a few propagules. For this reason, in vitro propagation techniques are an alternative to increase the number of plants obtained and thus be able to recover this valuable plant genetic resource. Temporary immersion systems (TIS) offer the advantage of mass-propagating plants for different purposes. This chapter describes a large-scale micropropagation protocol for Guarianthe skinneri using temporary immersion bioreactors (TIB).

Screening of endophytic fungi from Cremastra appendiculata and their potential for plant growth promotion and biological control

Biocontrol fungi are widely used to promote plant growth and pest control. Four fungi were isolated from Cremastra appendiculata tubers and screened for plant growth-promoting and antagonistic effects. Based on the morphological characterization and ITS, 18S rRNA and 28S rRNA gene sequencing analysis, the fungi were identified to be related to Colletotrichum gloeosporioides (DJL-6), Trichoderma tomentosum (DJL-9), Colletotrichum godetiae (DJL-10) and Talaromyces amestolkiae (DJL-15). The growth inhibition tests showed that the four isolates had different inhibitory effects on Colletotrichum fructicola, Alternaria alternata and Alternaria longipes, among which DJL-9 showed the highest inhibitory activity. Their culture filtrates (especially that of DJL-15) can also inhibit pathogens. Four isolates were positive for the production of indole-3-acid (IAA) and β-1,3-glucanase and possessed proteolytic activity but were negative for the production of iron siderophore complexes. The four fungi showed strong nitrogen fixation and potassium dissolution abilities. In addition to DJL-9 being able to solubilize phosphate, DJL-10 was able to produce chitinase and cellulase. Pot experiments indicated that the four fungi increased the germination rate of C. appendiculata and soybean seeds and increased soybean radicle growth and plant biomass. Among them, DJL-6 had a better growth-promoting effect. Therefore, we successfully screened the biocontrol potential of endophytes from C. appendiculata, with a focus on preventing fungal diseases and promoting plant growth, and selected strains that could provide nutrients and hormones for plant growth.

Geodorum laxiflorum Griff. (Orchidaceae), a new distribution record for Maharashtra state of India

Geodorum laxiflorum Griff., an endemic orchid of India is collected for the first time in Maharashtra state. Gadchiroli district is a much known district of the state for its rich biodiversity.

Comparative Transcriptome Analysis of Genes Involved in Sesquiterpene Alkaloid Biosynthesis in Trichoderma longibrachiatum MD33 and UN32

Trichoderma longibrachiatum MD33, a sesquiterpene alkaloid-producing endophyte isolated from Dendrobium nobile, shows potential medical and industrial applications. To understand the molecular mechanisms of sesquiterpene alkaloids production, a comparative transcriptome analysis was performed on strain MD33 and its positive mutant UN32, which was created using Ultraviolet (UV) mutagenesis and nitrogen ion (N⁺) implantation. The alkaloid production of UN32 was 2.62 times more than that of MD33. One thousand twenty-four differentially expressed genes (DEGs), including 519 up-regulated and 505 down-regulated genes, were identified. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed 139 GO terms and 87 biosynthesis pathways. Dendrobine, arguably the main sesquiterpene alkaloid the strain MD33 produced, might start synthesis through the mevalonate (MVA) pathway. Several MVA pathway enzyme-coding genes (hydroxy-methylglutaryl-CoA synthase, mevalonate kinase, and farnesyl diphosphate synthase) were found to be differentially expressed, suggesting that physical mutagenesis can disrupt genome integrity and gene expression. Some backbone post-modification enzymes and transcript factors were either discovered, suggesting the sesquiterpene alkaloid metabolism in T. longibrachiatum is a complex genetic network. Our findings help to shed light on the underlying molecular regulatory mechanism of sesquiterpene alkaloids production in T. longibrachiatum.