Detection of DNA specific sequences of Spongospora subterranea in soil and potato tubers

A test has been developed for early identification of the casual agent for potato powdery scab (Spongospora subterranea fs subterranea). Identification was carried out in seeds and soil where this tuber is grown. A polymerase chain reaction (PCR) was set up for detecting 372, 390 and 391 bp ribosomal DNA internal transcribed spacer sequences (ITS) in the S. subterraneagenome. A method for extracting and purifying DNA from infected plant material (potato root nodes and pustules on the potato) was standardised. Plant tissue was obtained by potato tuber propagation using an inoculum from the pathogen in greenhouse conditions. After the PCR had been optimised and its sensitivity determined, a molecular methodology was validated by examining plant material infected with S. subterranea and soil samples infested with the pathogen obtained from the departments of Cundinamarca and Nariño. The PCR detected S. subterranea DNA from infected material and soil samples (all thirty samples from the experimental area analysed proved PCR positive). These results show that this molecular method was not just useful for the early detection of the pathogen in soil samples but as a tool for detecting or determining the possible presence of this micro-organism in places that have been declared f ree of S. subterranea and an effective form of quality control in producing the certif ied potato seed. Key words: Powdery scab, cystosori, internal transcribed spacer, PCR, plasmodiophorid