Evaluation of herbal extracts for apple virus eradication compared to chemotherapy and thermotherapy

Native Iranian apples were sampled for apple chlorotic leaf spot virus (ACLSV) and apple stem grooving virus (ASGV) using ELISA and RT-PCR. Two indirect thermotherapy treatments (38º C for periods of 8 and 13 days) and three chemotherapy treatments each at two concentrations (Ribavirin (RBV) 20 and 40 mg/l, extracts of Hypericum perforatum (HPR) and Pelargonium sidoides (PLG) 60 and 120 mg/l) were applied to treat the viral contaminations. Thermotherapy for 13 days eliminated 100% of ASGV in cultivar GolBahar while RBV at 40 mg/l removed 100% of ACLSV. Cultivar ‘Soltani Shabestar’ became ASGV free using RBV at 20 mg/liter. ACLSV and ASGV contaminations were also reduced in cultivars Soltani Shabestar and Sharbati to 20 and 33.5 percent with the HPR treatment, apart from the limited number of remaining samples and the uncertain result, which were found simultaneously free of the two viruses. Both extracts damaged the explants at high concentrations, but at lower concentrations a limited number of explants of GolBahar could survive, though with no virus removal. There was complete concordance between the results of all positive samples detected by ELISA and RT-PCR. The use of herbal extracts in place of chemical compounds may be a promising method to eradicate plant viruses in fruit trees including apples. No trace of ASPV and APMV was detected in the explants under exam.