Biological aspects on the cultures of the entomophthoralean fungusPandora delphacis grown on broomcorn millets

Abstract

A novel method was developed to use glutinous broomcorn millets (Panicum miliaceum L.) as solid substrate to make cultures of the entomophthoralean fungusPandora delphacis specifically pathogenic to planthoppers, leafhoppers and aphids. Steamed millets with water content of 45% were inoculated with a liquid culture ofP. delphacis at a ratio of 20% (v/w) and then incubated at 25°C and L:D 12:12. The millets cultured for 3–17 d exhibited high potential for conidial production. The 5-d-old millet culture sporulated most abundantly, discharging up to 17.12 (±1.31) × 104 conidia/ millet. The cultures incubated for 7–11 d also had a satisfactory sporulation capability, yielding 13.00–13.90 × 104 conidia/millet. Compared to 2.32 (±0.34) × 104 conidia discharged from each ofMyzus persicae adults killed byP. delphacis and a ≤60-h duration of sporulation, each of the millets cultured for 5–11 d produced 5.6–7.4 times more conidia with an over doubled duration for conidial discharge (144 h). Among 106M. persicae adults exposed to the shower of conidia discharged from the cultured millets, a total mortality of 69.8% caused byP. delphacis infection was observed within 7 d after exposure, but no death was attributed to the fungal infection in the aphids unexposed. The results indicate that the millet cultures ofP. delphacis are biologically similar to aphid cadavers killed by the same fungus. Due to the superiority of the cultured millets to the cadavers in sporulation potential and duration, the method for making cultures ofP. delphacis on the broomcorn millets is highly recommended for use in study of entomophthoralean fungi for microbial control. This is the first report on the success of the solid culture ofPandora species on cereals.