Morpho-molecular characterization of &lt;i&gt;Ceratobasidium&lt;/i&gt; sp.: A mycorrhizal fungi isolated from a rare epiphytic orchid &lt;i&gt;Gastrochilus calceolaris&lt;/i&gt; (J. E. Sm.) D. Don

Mohammad Musharof Hossain

doi:10.3329/bjpt.v26i2.44584

Abstract

A mycorrhizal fungus, Ceratobasidium sp. GC (NCBI Gene Bank Accession no GQ369961) associated with the roots of an epiphytic orchid Gastrochilus calceolaris was investigated by cultural morphology, microscopic features and molecular analysis of Internal Transcribed Spacer (ITS) regions sequences of nuclear ribosomal DNA. The colony appearance of the fungal endophyte was fluffy growth pattern and the colour of the young colony was milky white on both surfaces that turned in to brown at maturity on the upper surface and deep brown on reverse surface. The microscopic features of the fungus i.e. hyphal diameter, multi-nucleate vegetative cells, right angle branching pattern with slight constriction at branching point and a dolipore septum near the branching point were observed. All the characters corroborated the identity with anamorphic Rhizoctonia like fungi. The ITS regions sequences of nrDNA and phylogenetic analysis based on the neighbor-joining method showed clustered with Rhizoctonia like fungi, and the maximum identity (98.28%) with Ceratobasidium RR and Ceratobasidium FPUB isolated from Rhynchostylis retusa and Dactylorrhiza hetagera, respectively. Thus, the ITS of nrDNA sequences validated the morphological data. This is the first report of orchid mycorrhizal fungi from Bangladesh.

Highlights

Mycorrhizal fungi are fundamental in orchid growth and metabolism, and influence the distribution and rarity of these delicate plants
The existence of mycorrhizal associations has been established since long in orchids with certain heterogeneous groups of fungi (Hadley, 1982). It is a biotrophic mutualistic symbiosis prevalent in more 90% of the higher plants in which both partners benefited in terms of nutrients exchange, evolution and fitness
Seed germination in orchids is totally dependent on mycobionts due to lack of sufficient food reserves (Smith and Read, 1997)

Summary

Introduction

Mycorrhizal fungi are fundamental in orchid growth and metabolism, and influence the distribution and rarity of these delicate plants. The existence of mycorrhizal associations has been established since long in orchids with certain heterogeneous groups of fungi (Hadley, 1982). It is a biotrophic mutualistic symbiosis prevalent in more 90% of the higher plants in which both partners benefited in terms of nutrients exchange, evolution and fitness. Orchids are categorized as myco-heterotropic, holomycotropic and mixotropic based on their nutritional dependency on fungal partner (Dearnaley, 2007). The orchids which depend on mycorrhizal fungi during seed germination stages only are referred as mycoheterotropic. The third orchid nutritional mode exists mixotrophy Such orchids are photosynthetic at the adult stage but augment their nutrition requirements specially carbon via mycorrhizal fungi (Dearnaley, 2007).

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