Morphological and ribosomal DNA- based characterization of commercial Cordyceps militaris strains in Thailand

Abstract

Cordyceps militaris, an entomopathogenic fungus, has been extensively utilized for many years as functional food and for medicinal remedies in Thailand. The fungus has numerous strains which are commonly sold in herbal markets and not all have been identified. Seven commercial C. militaris isolates (Cmi1, Cmi2, Cmi3, Cmi4, Cmi5, Cmi6 and Cmi7) were studied using macroscopic studies. The stromatal colour of seven isolates were golden yellow. Of these, six isolates had a cylindrical stipe of stromata (approximately 0.3-0.4 cm wide x 4-6 cm long) with a round cap, except the Cmi4, stroma had the widest stipe (approximately 1.5-2.5 cm wide and 2-4 cm long) with a shape cap. Moreover, the mycelium had the highest mycelial growth rate, but only the Cmi4 had the lowest. To determine the stromatal characteristics using cross section technique and observing under a microscope, the result revealed that all isolates were golden yellow at the edge, and colourless at hyphae. To investigate the spore characteristics using the spore shooting technique, and observing under a microscope, the result revealed that most spores were globular shape. To study the conidial formations and hyphae characteristics using the slide culture and SEM techniques, the result showed that most spores had globose and oval shapes, moreover these germinated and produced long hyphae. The conidia formed mostly single globe heads and rare group globe heads in short chains and subtending conidia. Some conidia had pyriform or cylindrical shapes. Genetic variation among the seven isolates gave 100% nucleotide-sequence homology at the ITS and 28S rDNA regions. These data suggested that the macroscopic method was a highly powerful tool for strain identification of C. militaris.

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