Factors affecting the sporulation capacity during long-term storage of the aphid-pathogenic fungus Pandora neoaphidis grown on broomcorn millet

Aphid-pathogenic fungus, Pandora neoaphidis, grown on broomcorn millet possesses greater sporulation capacity (Cs) than aphid cadavers. The most sporulating cultures (32.0 × 104 spores millet−1 grain) with water content (Cw) of 48.7% were prepared by incubation at 20 °C for 15 days and used to study the effect of temperature and humidity on Cs during long-term storage. Cultures were sealed with paper to retain ambient humidity, with parafilm for saturated humidity, or kept in 85% and 98% RH chambers. The Cw and Cs were monitored during 200-day storage at 5-20 °C. The paper-sealed cultures at 5 °C, associated with 21-25% of Cw, were best preserved and their 120-day Cs was similar to that of the fresh cadavers. Consistently or variably high RH at 5 °C resulted in significantly higher Cw and lower Cs despite longer viability. The regimes at ⩾10 °C preserved the cultures for ⩽40 days. The observations fit well to the logistic model Cs = 35.28/{1 + exp[−2.36 + (−0.003Cw + 0.001CwT)t]} (r2 = 0.95) for all regimes of temperature (T) or Cs = 35.55/[1 + exp(−2.33 + 0.001Cwt)] (r2 = 0.93) at 5 °C only. The rate of decline of Cs of −0.003Cw + 0.001CwT or 0.001 Cw over days (t) highlights the primary effect of Cw. The daily Cs-decline rates obtained for the best-stored cultures and air-dried cadavers stored at 5 °C were surprisingly identical. The results suggest a possible cheap method for preparing and storing large quantities of P. neoaphiodis inocula.