Orchids - Mycorrhizae

J. Orchid Soc. India, 33: 23-29, 2019 ISSN 0971-5371 ORCHIDS - MYCORRHIZAE C Manoharachary Department of Botany, Osmania University, Hyderabad– 500 007, Telangana, India Abstract The present paper includes data on orchid flora available from Andhra Pradesh, their endemics, and also reviews the orchid-mycorrhizal status along with author’s data on orchidoid mycorrhiza. Introduction plants of Aerides odorata are known to be used in curing tuberculosis (Dash et al., 2008). Leaves and stem of PLANT DIVERSITY is quite amazing in structure, Cleisostoma williamsonii have found place in Ayurveda function and economic value. Orchids are not only for curing bone fractures, while root extract of Calanthe important in medicine but also add beauty and charm triplicata is used in controlling diarrhoea and tooth to the landscape. IUCN report (Anonymous, 1996) has cavities. Tubers of Epipactis latifolia are used to cure recorded 20,000 orchid species in the world. Most of nervous disorders, while tuber extract of E. nuda is the orchids are distributed between 30° North and South said to be useful as a blood purifier. The flowers of of Equator. High rainfall, relative humidity, Dendrobium hookerianum yield dye whereas whole plant temperatures, substratum, latitude and altitude affect of Habenaria clavigera may find place as an anti AIDS distribution of orchid flora. Greater diversity of orchids agent. is found in the tropics. Orchidaceous plants occur as epiphytes, lithophytes, terrestrials and as saprophytes. The orchid flowers with their varied colors, sizes and Charaka Samhita and other ancient books have recorded beauty attract the attention of entrepreneurs, the medicinal value of orchids and awareness of these floriculturists, pharmacists, amateur orchid lovers, and plants dates back to Vedic period. Classical work of others. Nowadays, orchid growing has become a Hortus malabaricus by Van Rheede (1678-1693) commercial project. It is a multi-million dollar business introduced Indian orchids. About 1296 species in Netherlands, California, Thailand, and Singapore. belonging to 155 genera of orchids are recorded from The orchids represent 8-10% of the international market. India (Singh et al., 2019) and constitutes 6% of the At present, India represents 1% of orchid market in the world orchids. Orchids account for nearly 8% of world indicating that orchid industry is still at its angiosperm species diversity (Chase et al., 2015; Willis, embryonic stage. The over exploitation and habitat 2017). The predominantly occurring orchids are destruction made some species of Dendrobium, Bulbophyllum, followed by Dendrobium, Eria, Habenaria, Paphiopedilum, Vanda etc. rare and led to their entry Oberonia and others. The Eastern Himalayas represent into the Red Data Book. Nearly 147 species of orchids 870 species of orchids belonging to 160 genera and in the Indian sub continental region are under threat. 290 species of orchids are known to occur in Western Protection of natural habitats, encouraging biosphere Himalayas. About 380 species are distributed in reserves, multiplication of orchids in botanical gardens, peninsular regions. Andaman and Nicobar Islands orchidaria and other measures will help in conserving represent 115 genera. the orchid flora. Setting of seed/gene banks and multiplication through tissue culture (Anuprabha et al., Orchid genera have become important as commercial 2017; Arora et al., 2016; Decruse and Gangaprasad, product because of their great potential in horticulture. 2018; Kaur et al., 2017; Pathak et al., 2017; Sibin and There are more than one lakh registered hybrids all over Gangaprassad, 2016) will ensure conservation. The the world representing Aerides, Calanthe, Coelogyne, Botanical Survey of India has brought several Cymbidium, Dendrobium, Vanda etc. Orchids are not threatened species of orchids under cultivation at only known for their ornamental value but many of them orchidaria in Howrah, Shillong and Yercaud. Orchids are used in traditional medicine as well (Pathak et al., contribute to the rich plant wealth of India as they have 2010). The leaves of Vanda tessellata and roots of medicinal value, besides being important in floriculture. Acampe praemorsa are used to cure rheumatism Orchid taxa from Andhra Pradesh are represented by (Ahmed et al., 2002 and Kumar et al., 2000). Whole 78 species belonging to 36 genera. These include Received: August 18, 2018; Accepted: February 20, 2019 J. ORCHID SOC. INDIA (DECEMBER 30, Acampe, Aerides, Bulbophyllum, Cymbidium, A number of fungi found in orchid mycorrhizae belong Dendrobium, Eulophia, Habenaria, Liparis, Nervilia, to the anamorphic genus Rhizoctonia. They include Oberonia, Pholidota, and Vanda. Habenaria ramayyana teleomorphic genera Sebacina, Thanatephorus, is an endemic, while Geodorum densiflorum and Vanda Tulasnella. Non-chlorophyllous orchids often seem to tessellata are common orchids of Andhra Pradesh (Raju parasitize basidiomycetes, including members of et al., 2008). Armillaria, Coriolus, Favolaschia, Fomes, Hymenochaete, Marasmius, Thelephora, Tomentella, Orchid Mycorrhizae and Xerotus. Fungi obtain carbohydrates outside of orchid from a variety of other sources. Many of these Orchidoid mycorrhizae are characteristic of fungi are saprophytic, able to break down dead organic approximately 20,000 species in the family matter in the soil. Armillaria mellea, Rhizoctonia solani/ Orchidaceae. Orchids pass through an obligate Thanatephorus cucumeris are better known as plant mycoparasitic stage in the course of normal pathogens while others are ectomycorrhizal in the roots development. Orchid seeds are dust like, having minute of some trees. Orchid taxa vary in their fungal spherical embryo with no endosperm and a thin seed specificity and the embryos of photosynthetic orchids coat. The seed cannot grow until a fungus has infected appear to form mycorrhizal associations with a fewer it. Fungal contact makes the orchid seed to grow into a fungal species than the adults. It is relatively common protocorm. Once the protocorm has grown to a sufficient to find many endophytic fungal species in adult orchids. size, the shoot starts to grow, producing a structure However, fungal isolates from adults have failed to termed the mycorrhizome, this helps in seedling growth. produce mycorrhizal associations with embryos of the Orchids grow in association with a number of fungi: same species. In the non-chlorophyllous orchids, all Armillaria mellea, Epulorrhiza, and Rhizoctonia solani available evidence suggests that the plants are highly (Hajong and Kapoor, 2016; Hossain et al., 2013) which host specific, parasitizing only one or a few fungal are well-known plants pathogens. Lab tests have shown species. Often, these plants are parasitized by that an embryo paired with the non suitable fungus can ectomycorrhizal fungi so that the carbohydrates that be quickly killed by the fungus. Thus, it is not surprising the orchid gains comes from the trees surrounding it. that orchids have specialized cells and structures for Kaushik (1983) reported mycorrhizal association in 53 mycorrhizae. In adult plants, much of the plant body species of the orchids showing fungal pelotons and contains antifungal phytoalexins (Hadley, 1982) and this hyphae in transections in cortical cells of roots with is presumably true of embryos and protocorms as well. photomicrographs and drawings; and elongated cells In orchid embryos, cells near the suspensor end enlarge packed with mycorrhizal pelotons and septate hyphae and undergo nuclear replication repeatedly, and then in photomicrographs of longitudinal sections prepared these cells are infected by the fungus, which forms a by microtomy of roots of Calanthe gracilis. tightly coiled hyphal structure termed as a peloton. As with all endocellular mycorrhizae, the fungus does not The fungal partners are generally able to break down actually penetrate the cell membrane. The dynamic complex organic materials; the orchids that grow with pelotons remain there for a longer time and then get them are able to tap unusual substrates for nutrients digested by the plant. The empty cells might be including the bog peat, highly calcareous soils, and the reinfected or the plant may enlarge new cells, so that dust and debris on tree branches. Indeed, minute and the band of mycorrhizae moves progressively down the highly dispersible orchid seeds and mycotrophic habit plant as it grows. Few orchids are infected seasonally are undoubtedly the features that made them successful and adults may be non-mycorrhizal for some part of as epiphytes. About 70% of the orchid species are the year. Others are continuously infected, but the epiphytic and they comprise perhaps two-thirds of infection is confined to enlarged cells. The roots often epiphytic vascular plant species. become mycorrhizal, and in some species, mycorrhizal root fragments can grow into new plants when they are Vij et al. (2002) have reviewed the status of orchidoid separated from the parent rhizome. There is an mycorrhiza in techniques to investigate them in an in- enormous variation in patterns of organ growth and depth manner. Vij and Sharma (1983, 1988) have studied mycorrhiza across orchid genera and the variation the mycorrhizal association in North Indian orchidaceae across the family is likely to be one of the reasons that and mycorrhizal endophytes. Further, Vij et al. (1985) is why orchids have been able to live in so many have elaborately documented mycorrhizal endophytes different habitats throughout

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