Molecular identification of Venturia asperata from atypical scab-like symptoms on apples in Italy

Similar apple scab symptoms were first observed at the end of July in 2012 in the Northern Italy (Cesena) on fruits of apple cultivar Modì carrying the Rvi6 major resistance gene to Venturia inaequalis. The aim of this work was to identify the causal agent of the atypical scab-like symptoms by molecular techniques. Symptomatic fruits were collected during May in one orchard in 2015. Ten monoconidial isolates were obtained through recovering the conidia from about 10 fruits. Conidial suspension was then streaked on Petri dishes of water agar amended with streptomycin sulfate. After 24 h of incubation at 20°C, single germinated spores were selected under stereomicroscope, then picked up and placed on PDA amended with three antibiotics. The isolates were cultivated at 20°C until molecular characterization together with the reference strain of Venturia asperata. Amplification of ITS fragments was carried out for specifically amplify rDNA of V. asperata, V. inaequalis and Venturia pirina. Approximately 4-5 hyphae were removed from each isolate and transferred without DNA extraction to the PCR tube with the addition of BSA. DNA amplification was obtained for all isolates by primers specific for V. asperata, while no amplification was observed using primers specific for V. inaequalis and V. pirina. These results point out the presence of V. asperata from the atypical scab-like symptoms but further studies are in progress to have a more precise identification of the pathogen.