SEED AND BUD PROPAGATED PLANTLETS CAN BE USED TO DOUBLE CHECK THE PRESENCE OF MIXED VIRAL INFECTIONS AT APPLE

Two apple cultivars, Golden delicious and Starking grown in Devoll, Albania, were analyzed to verify the rate of infection by ApMV (Apple Mosaic Virus), ASGV (Apple Stem Growing Virus), ACLSV (Apple Chlorotic Stem Virus) and ASPV (Apple Stem Pitting Virus) using in vitro propagated plantlets, and results taken from different categories of explants and among collections were compared based in the fact that template concentrations were equal. Samples, in total 450 trees, were buds taken from branches collected in early spring from symptomless trees, and seeds taken from fruits at three collection orchards during consecutive years 2013, 2014, 2015. Total RNA was extracted from plantlets grown in vitro from buds and seeds, which were used as template for One-step RT-PCR detection of the viruses. Results showed that viruses are present in both cultivars from the three collection orchards. Concentrations of amplicons varied among cultivars, explants categories and from collection to collection, which suggested different infection rates. The presence of mixed latent viral infection was discussed in terms of a possible mechanism of cross-protection among viral strains already amplified, and concentration of amplicons considered proportionate to the infection rate, was seen as a tool to monitor the situation in collections even in the absence of field symptoms.