Variation of resistance response of orchids induced by Rhizoctonia against the infection of Odontoglossum ringspot virus (ORSV) based on percentage of disease development

Orchid is one of the largest groups of flowering plants that are in great demand by society. Besides, the various flowers with a long vase life, the price of orchids is also stable and affordable. Phalaenopsis and Dendrobium are the most popular types of orchids. To anticipate this, orchid cultivation needs to be improved. However, orchid cultivation is not always accompanied by the effort of disease prevention, particularly those caused by viruses. The virus that most infects orchids is the Odontoglossum ringspot virus (ORSV). Symptoms that appear on the leaves are chlorosis, mosaic with a pattern of lines, circles, and necrotic rings/rings. Control of viral infections can utilize organisms that are able to induce resistance, namely mycorrhizae. Mycorrhizae will penetrate into the root cortex tissue and provide nutrients for the orchid. Mycorrhizae that are quite often found are Rhizoctonia and are applied by induction to orchids. Induction was undertaken by planting orchids in Rhizoctonia inoculum until anatomically a peloton structure (solid coils) was formed on the orchid roots. The aim of this study was to study the response of orchid plants in the form of percentage incidence and intensity of the disease and the level of plant resistance to ORSV infection in Phalaenopsis amabilis and Dendrobium discolour which had been induced by Rhizoctonia. This research was conducted at the Laboratory of Botany, Biology, FMIPA, Universitas Lampung, using a factorial completely randomized design (CRD). Factor 1 was the type of orchid and factor 2 was mycorrhizal induction, virus inoculation, and a combination of both with 4 replications. The finding indicated that Phalaenopsis amabilis was more susceptible to ORSV infection than Dendrobium discolour based on a higher incidence and intensity of the disease. Mycorrhizal induction and virus inoculation (MAV) in Dendrobium discolour showed an increase of resistance response compared to Phalaenopsis amabilis.

An ancestral signalling pathway is conserved in plant lineages forming intracellular symbioses

ABSTRACTPlants are the foundation of terrestrial ecosystems and their colonization of land was facilitated by mutualistic associations with arbuscular mycorrhizal fungi. Following that founding event, plant diversification has led to the emergence of a tremendous diversity of mutualistic symbioses with microorganisms, ranging from extracellular associations to the most intimate intracellular associations, where fungal or bacterial symbionts are hosted inside plant cells. Through analysis of 271 transcriptomes and 122 plant genomes, we demonstrate that the common symbiosis signalling pathway controlling the association with arbuscular mycorrhizal fungi and with nitrogen-fixing bacteria specifically co-evolved with intracellular endosymbioses, including ericoid and orchid mycorrhizae in angiosperms and ericoid-like associations of bryophytes. In contrast, species forming exclusively extracellular symbioses like ectomycorrhizae or associations with cyanobacteria have lost this signalling pathway. This work unifies intracellular symbioses, revealing conservation in their evolution across 450 million years of plant diversification.

Main fungal partners and different levels of specificity of orchid mycorrhizae in the tropical mountain forests of Ecuador

Orchids are a main component of the diversity of vascular plants in Ecuador with approximately 4000 species representing about 5.3% of the orchid species described worldwide. More than a third of these species are endemics. As orchids, in contrast to other plants, depend on mycorrhizal fungi already for seed germination and early seedling establishment, availability of appropriate fungi may strongly influence distribution of orchid populations. It is currently debated if green orchids depend on specific mycobionts or may be equally promoted by a broad spectrum of mycorrhizal fungi, discussion mostly based on data from temperate regions. Here we summarize results obtained from broad scale investigations in the tropical mountain rain forest of Ecuador revealing associations with members of Serendipitaceae (Sebacinales), Tulasnellaceae, Ceratobasidiaceae (Cantharellales), and Atractiellales. Recent molecular data show that these worldwide spread fungal groups have broad ecological implications and are specifically suited as mycorrhizal fungi of green orchids. We found that main fungal partners and different levels of specificity among orchids and their mycobionts in the tropical mountain forests correspond to findings in other biomes despite the large ecological differences.

Controlling Rhizoctonia Damping-off of Chinese Mustard by Using Endomycorrhizal Rhizoctonia spp. Isolated from Orchid Mycorrhizae

Inoculation of hypovirulent Rhizoctonia spp. has been recognized as an effective strategy for protecting plants against damping-off caused by pathogenic Rhizoctonia spp. In this study, endomycorrhizal Rhizoctonia spp. isolated from fungal pelotons in orchid plants were used for controlling Rhizoctonia damping-off of Chinese mustard. According to phylogenetic analysis and anastomosis group (AG) determination, the virulence of three isolates of multinucleate Rhizoctonia solani in AG-6; eight isolates of binucleate Rhizoctonia in AG-A, AG-B, AG-G, AG-P, and AG-R; and two isolates of binucleate R. repens were evaluated using test plants. All isolates, except that in AG-R, caused low disease severity in 10-day-old radish (0.10 to 0.61), cucumber (0.28 to 0.54), and Chinese mustard (0.18 to 0.65). By contrast, pathogenic isolates in AG-4 killed almost all test plants with symptoms of collapsed hypocotyl and wilted leaves (0.88 to 0.96). Of the 13 endomycorrhizal Rhizoctonia isolates assessed, AG-P isolates Cno10-3 and CalS1-2 provided 91 and 100% protection, respectively, against R. solani AG-4 in 26-day-old Chinese mustard. This study revealed that endomycorrhizal Rhizoctonia spp. in orchid have the potential to biologically control damping-off of Chinese mustard.

Tropical orchid mycorrhizae: potential applications in orchid conservation, commercialization, and beyond

Orchid mycorrhizae are unique interactions in the plant kingdom involving all the orchids and a variety of fungi including Rhizoctonia. Orchids are one of the most charismatic plant families and include at least 20,000 species widely appreciated by specialist growers and scientists. They also include Vanilla, source of one of the most traded spices worldwide. Most mycorrhizal fungi belong to a group of basidiomycetes widely known for their pathogenic interaction with many crop plants including potatoes, rice, and beans. The main application of orchid mycorrhizal fungi is in the propagation of endangered and commercial orchid species, but we have recently documented an alternative use. The fungal symbionts of orchids have the ability to induce resistance to Rhizoctonia in rice plants, which opens new possibilities of biological control agents never previously imagined.

Mycorrhizae and mycorrhizal fungi of boreal species of Platanthera and Coeloglossum (Orchidaceae)

The seasonal development and mycorrhizal fungi of the mycorrhizae of Platanthera hyperborea, Platanthera obtusata, Platanthera orbiculata, and Coeloglossum viride are described. Fungal endophytes belonging to the following taxa were identified: Leptodontidium orchidicola, Epulorhiza repens, Epulorhiza anaticula comb, nov., and Ceratorhiza goodyerae-repentis. In addition, anamorphic material of a species tentatively identified as Sebacina sp. was found solely in the mycorrhizae of P. orbiculata. A series of isolates bearing distinctive, clamped monilioid cells and belonging to an unidentified species of Sistotrema was found in P. obtusata. This is the first report of a Sistotrema species from orchid mycorrhizae. An isolate from C. viride, with broad hyphae, large globose monilioid cells, and dark brown mycelium, resembles Burgeff's 1936 description of Rhizoctonia anomala nom.inval. This taxon is validated, redescribed, and presented as the new species Moniliopsis anomala.