Elimination effect of electrotherapy and cold therapy combined with chemotherapy on apple scar skin viroid on in vitro apple plants

Abstract

Apple scar skin viroid (ASSVd) and other apple viruses [apple chlorotic leaf spot virus (ACLSV), apple stem-pitting virus (ASPV), and apple stem grooving virus (ASGV)] can cause significant economic losses to the apple industry. We used ASSVd- and ASGV-infected Malus pumila ‘Spy 227’ and ACLSV-, ASPV-, and ASGV-infected Malus ‘Gala’ apple plants as the plant materials for virus elimination experiments. We evaluated the viral elimination effectiveness of electrotherapy at different electric current intensities and treatment durations on in vitro plants of the two apple cultivars. Furthermore, the effect of cold therapy (4°C) combined with ribavirin (25 µg/mL) at different treatment durations on Spy 227 plants was investigated. All shoot tips of the two cultivars sterilized with 75% alcohol or 0.1% mercury bichloride grew normally after treatment with an electric current. Spy 227 plants treated with cold therapy combined with ribavirin started to die after 50 days of treatment, and the death rate increased with the extension of treatment time. Quantitative reverse-transcription PCR (qRT-PCR) and RT-PCR were used to detect the viroid and viruses in regenerated plants. The results showed that electrotherapy did not inhibit ASSVd, ACLSV, ASGV, or ASPV. Moreover, cold therapy combined with ribavirin had no eliminating effect on ASSVd, but the elimination rate of ASGV under treatment periods of 80 d and 95 d was 60.4% and 60.1%, respectively. Considering the impact of ASSVd on apple plant health, additional methods are necessary to effectively remove this viroid.