Optimising inoculum yield and shelf life of Plectosphaerella cucumerina, a potential bioherbicide for Cirsium arvense

ABSTRACTPlectosphaerella cucumerina was identified as a potential bioherbicide for controlling Cirsium arvense in Canada and New Zealand. The current study evaluated production conditions using two isolates (one from each country) to determine whether the yield and shelf life of inoculum are suitable for mass production. Mycelial growth and sporulation in culture both increased from 15°C to 25°C and declined at higher temperatures with no mycelial growth at 37°C. The Canadian isolate produced fewer conidia than a New Zealand isolate. Potato dextrose-based liquid media with moderate to high concentrations of carbohydrates (25%, 50%, and 100%) maximised conidia production and these base media produced conidia with the highest germination rate (>80%) both at harvest and after 4 weeks stored at 4°C in 2.5% glycerol, 40% milk glycerol or after air drying. However, after 10-week storage, the conidia failed to germinate. Sporulation occurred during growth on all solid substrates tested (rice, rolled barley, and ...