Coconut Water as a Promising Culture Media for Hirsutella thompsonii Fisher, a Pathogen of Coconut Mite

Abstract

Coconut eriophyid mite Aceria guerreronis Keifer has emerged as a major pest of coconut in the country since 1998. Among the various biocontrol agents, Hirsutella thompsonii is a promising fungal pathogen used in field biosuppression of the pest. Influence of various synthetic and laboratory-derived growth media, viz., Potato Dextrose Agar (PDA), Sabouraud Dextrose Agar (SDA), Glucose Yeast Extract Agar (GYA), and Carrot Agar (CA), was compared with a locally available inexpensive substrate, coconut water on growth, and sporulation of H. thompsonii. Fungal growth characters, viz., radial growth, conidial production, and micromorphometry of the fungal mycelium and spore, were recorded. Results indicated comparable growth in coconut water media (1.91 cm/20 days) to that of PDA (1.94 cm/20 days). In solid media, laboratory-derived coconut water agar showed significantly higher spore count (12.9 × 104spores/cm3) followed by laboratory-derived PDA (11.38 × 104spores/cm3). Regarding conidial production in broth culture, maximum spore production of H. thompsonii was observed in Sabouraud Dextrose broth (51.2 × 104spores/cm3). Coconut water showed comparable spore count (18.2 × 104spores/cm3) to that of Potato Dextrose broth (19.6 × 104spores/cm3) and Glucose Yeast Extract broth (18.6 × 104spores/cm3). There was no significant difference in micromorphometric characters among the media tested. The results suggest the potential of using coconut water for mass production of H. thompsonii in the laboratory.