Investigating hyperparasites as potential biological control agents of rust pathogens on cereal crops

Rust pathogens cause damage to cereal crops around the world, leading to reduced yield and profit. Current methods of rust control include fungicides, resistant cultivars, and preventative agronomic practices. Some hyperparasites are antagonists of plant pathogens and may provide a potential method of biocontrol against increasingly virulent strains of rust. Very little is known about the mechanism of inhibition of rust growth by hyperparasites, however, isolation of new strains and subsequent characterisation may reveal new treatment strategies for the control of rust. Here we report the isolation of six new fungal hyperparasites and their effects on the development of three Puccinia rust pathogens were examined in vitro, to determine the potential of each as biocontrol agents of rust. Cut-leaf sections of rust-susceptible wheat, barley and oat cultivars were treated with fungal hyperparasite conidia prior to infection with the rust species; Puccinia triticina, P. hordei, and P. coronata f. sp. avenae, respectively. Inhibition of rust spore germination tests were also performed on water agar plates co-inoculated with the isolates. In leaf sections, rust pustule number was significantly (P < 0.01) lower for all six isolates tested: Penicillium brevicompactum, Clonostachys rosea, Simpicillium aogashimaense, Neoascochyta sp., Lecanicillium psalliotae and Epicoccum nigrum. The results of these experiments suggest that the mechanisms underlying the reduction in pustule number could include one or more of the processes of direct parasitism, antagonism by antibiosis, competition, and/or induction of host plant resistance.