Potato powdery scab is caused by Spongospora subterranea f. sp. subterranea, an obligate parasite and soil-borne pathogen which affects the root system and tubers. It is also a vector of the pomovirus Potato mop-top virus (PMTV). This organism has resistance structures called cystosori which allows it to remain in the soil for years. This study aimed to determine the optimal conditions of temperature, inoculum sources and substrate for zoospore release, for future use in infectivity assays. Three experiments were conducted in which three inoculum sources (soil, roots and tubers), three liquid substrates (water, root extract and nutrient solution) and different temperatures were tested. Observations of mobile zoospores were made in a light microscope equipped with a Neubauer chamber, from 24 until 120 hours after inoculation. Significant differences were found among the different treatments, with the optimal conditions using root extract as inoculum source, temperature between 15 and 20°C, from 24 until 96 hours after inoculation.
Cystosori; inoculum; powdery scab
