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PCR assays for diagnosis of postharvest fruit rots and early detection of Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens in apple fruit.
P. SIKDAR (1), P. Okubara (2), M. Mazzola (3), C. Xiao (4). (1) Washington State University, Wenatchee, WA, U.S.A.; (2) USDA-ARS, Root Disease and Biological Control Research Unit, Pullman, WA, U.S.A.; (3) USDA-ARS, Wenatchee, WA, U.S.A.; (4) USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA,

Speck rot caused by <i>Phacidiopycnis washingtonensis</i> and Sphaeropsis rot caused by <i>Sphaeropsis pyriputrescens</i> are two recently reported postharvest diseases of apple. Fruit infection by the pathogens occurs in the orchard, but symptoms develop after harvest and are similar to that of gray mold caused by <i>Botrytis cinerea</i>. Accurate diagnosis and detection of these diseases is important to disease inspection, particularly for fruit destined for export. The aim of this study was to develop PCR assays for disease diagnosis and early detection of latent infection in apple caused by <i>P. washingtonensis</i> and <i>S. pyriputrescens</i>. Species-specific primers based on rDNA-ITS region, that amplified only the target pathogens, but not non-target fungi commonly associated with apple fruit, were developed for PCR assays. Conventional and real-time PCR assays 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 as the inoculant. Real-time PCR assays effectively detected 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.<p><p>Keywords: Fungus, Fruits-Nuts, Apple

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