Effects of amendments to agar media on the in vitro growth of the entomopathogenic fungus Ophiocordyceps robertsii (Hook.) G.H. Sung, J.M. Sung, Hywel-Jones & Spatafora (Hypocreales: ophiocordycipitaceae)

Abstract

Two experiments were undertaken to determine the effect of agar amendments on the growth of the asexual (anamorph) stage of the entomopathogenic fungus Ophiocordyceps robertsii (Hook.) G.H. Sung, J.M. Sung, Hywel-Jones & Spatafora (Hypocreales:Ophiocordycipitaceae) in culture. These were part of ongoing research whose aim was to develop methods for augmenting O. robertsii infested ghost moth (Hepialidae) larvae (āwheto) populations in forests, with a view to assisting their potential commercial harvest. The first experiment used full-strength potato-dextrose agar (PDA) with added yeast while the second used a reduced concentration of PDA. Amendments included mycosed host (ghost moth larva) tissue, leaf litter, soil, hinau (Elaeocarpus dentatus (J.R.Forst. et G.Forst.) Vahl var. dentatus) leaves, berries, seeds and roots and combinations of these amendments. The hinau leaf amendment treatment stood out, unexpectedly causing a 53% reduction in fungal growth in the first experiment and a 100% reduction in the second. Several of the other amendments were associated with a small (up to 15%) reduction in fungal growth in both experiments while in the second experiment, with a reduced-agar content, some combinations of amendments that avoided the use of hinau leaves were associated with an increase in fungal growth of 24%–43%. While these experiments did not achieve the original objectives of developing amended media recipes for increasing O. robertsii growth rates, they do indicate that hinau leaves may contain chemicals with anti-fungal properties. The results are discussed in relation to recent discoveries of chemicals with strong anti-fungal properties in the leaves of an Elaeocarpus species in India. More research into the nature of New Zealand endemic Eleaocarpus spp. phytochemistry and its anti-fungal properties is warranted.