A methodology to detect and quantify five pathogens causing potato tuber decay using real-time quantitative polymerase chain reaction

Late blight (Phytophthora infestans), pink rot (Phytophthora erythroseptica), leak (Pythium ultimum), dry rot (Fusarium sambucinum), and soft rot (Erwinia carotovora subsp. carotovora and subsp. atroseptica) are particularly damaging diseases of stored potato tubers worldwide, In this study, we present a methodology to detect and quantify the causal agents of the five aforementioned diseases from whole potato tubers, using real-time quantitative-polymerase chain reaction. Six primer pairs were designed to amplify targets smaller than 150-bp DNA in single copy protein-coding gene targets of each of the pathogens and the potato host. Using a large collection of pure culture DNA samples, all primer pairs specifically detected the DNA target in the intended pathogenic species. Amplification efficiencies over a five-log dilution series ranged between 95 and 100% and were unaffected by the presence of large amounts of host DNA. The detection level of the primers reached 0.5 pg of target DNA. Pathogens were detected in 100 pg of total DNA extracted from 170 to 250 g of tubers, 4 days after inoculation, regardless of the presence of symptoms. The presence of P. etythroseptica, Pythium ultimum, or E. carotovora was also detected in 1 ng of DNA extracted from potato tubers collected from a commercial storage facility. This study provides the first step in a methodology to predict the storability of potato tubers following harvest.