Quantitative analysis of the lifelong production of conidia released from single colonies of Podosphaera xanthii on melon leaves using electrostatic techniques

Abstract

Using an electrostatic rotational spore collector, we consecutively collected all of the conidia produced from single colonies of melon powdery mildew (Podosphaera xanthii Pollacci KMP-6 N) on leaves of living melon plants throughout the lifetime of the colony in a natural environment, and counted all conidia that were attracted to insulators. The collector consisted of an insulated round plastic container, a conductor (copper) film, an insulator (collector) film, an electrostatic voltage generator and a timer mechanism. Negative charge was supplied from the voltage generator to the conductor film, and the negatively charged conductor film caused dielectric polarization of the insulator film. The insulator film, which creates an attractive force for trapping conidia that enter the field, was placed ca. 2 cm from the apex of the single colony. Released conidia were successfully attracted to the electrostatically activated insulator films. Each collector film was exchanged for a new insulator film at 24 h intervals until KMP-6 N ceased to release conidia from single colonies. During a colony’s lifespan, KMP-6 N released an average of 12.6 × 104 conidia from each of the single colonies at ca. 744 h. Additionally, we found that 1) the number of conidia released from single colonies in daytime was larger than that in night-time, 2) conidia were released from single colonies for ca. 2–4 h longer in spring or summer than in autumn or winter, and 3) release of conidia from KMP-6 N decreased as light intensity declined. Thus, conidial release from conidiophores is affected by day-length and light intensity.