Direct detection of Taphrina deformans on peach trees using molecular methods

The ascomycetous fungus Taphrina deformans is the agent of peach leaf curl, a worldwide disease of peach potentially devastating to both crop yields and tree longevity. Conspicuous leaf curl symptoms result from the invasion of host tissue by the strictly parasitic mycelial phase of the T. deformans dimorphic life-cycle. Successful isolation of the fungus in pure culture is cumbersome and limited to late spring/early summer (time of ascospore discharge from infected leaves) and only rarely has the asymptomatic yeast phase been isolated from buds. Molecular methods, namely those based on the hybridisation of nucleic acids, are advantageous for diagnostic purposes since they do not require isolation of the fungus on culture media. Direct amplification using the polymerase chain reaction (PCR) and fluorescent in situ hybridisation (FISH) were tested for diagnosis of peach leaf curl disease in order to provide a fast and reliable method for disease risk assessment. Specific primers and probes were designed based on available ribosomal DNA sequence data. Positive and specific diagnoses of peach leaf curl were achieved with primer TDITS1, using PCR-detection, and probe TDE634, using FISH, both on infected leaves and in washings of asymptomatic peach buds.