Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2012
Publication Date: 7/1/2012
Citation: Sikdar, P., Okubara, P.A., Mazzola, M., Xiao, C. 2012. PCR assays for diagnosis of postharvest fruit rots and early detection of Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens in apple fruit. Phytopathology. 102:S4.109-110.
Technical Abstract: Speck rot caused by Phacidiopycnis washingtonensis and Sphaeropsis rot caused by Sphaeropsis pyriputrescens are two recently reported postharvest diseases of apple. Infection of fruit by the pathogens occurs in the orchard, but symptoms develop after harvest and are similar to that of gray mold caused by Botrytis cinerea. Accurate diagnosis and detection of these diseases is important to disease inspection, particularly for the fruit destined for overseas. The aim of this study was to develop PCR assays for diagnosis of these diseases and early detection of latent infection in apple caused by P. washingtonensis and S. pyriputrescens. Species-specific primers based on rDNA-ITS region, that amplified only their corresponding target pathogens, but not non-target fungi commonly associated with apple fruit, were developed for PCR assays. Conventional and real-time PCR assays based on the specific primers were developed and validated using decayed fruit resulting from artificial inoculation in comparison with isolation-based assays. For wound-inoculated fruit, pathogens identified using PCR assays were consistent with those used for inoculation. For detection of latent infections, real-time PCR assays were able to detect latent infections in symptomless stem-end and calyx-end tissues of fruit that were inoculated with the pathogens in the orchard during the growing season. The PCR assays provide rapid, accurate methods for diagnosis and early detection of these diseases.