Analysis of virus structure variants in before- and after-thermotherapy-treated apple plants

Pre-thermotherapy apple plants and their homologous regenerated virus-infected apple plants were used to analyze the effect of high temperature on the structure of plant virus variants. The target bands of apple chlorotic leaf spot virus (ACLSV), apple stem grooving virus (ASGV), and apple mosaic virus (ApMV) in the plants of the two populations were purified and cloned, and 16 positive clones of each sample were randomly selected for single-strand conformation polymorphism (SSCP) analysis. The results showed that a predominant haplotype could be found in the two populations. The main variant was the same both in the regenerated and homologous treated plants, but the percentages in regenerated plants could be lower than, the same as, or higher than that in pre-thermotherapy plants. Two types could be divided depending on the percentage of the predominant haplotype in the treated plants, diversity (less 70%) and simple (more 80%), respectively. The clones of different haplotype in each isolates were sent to sequence, and the alignment results in accordance with that of the SSCP analysis. All the results indicated that thermotherapy could not affect the predominant variants of virus in treated plants, just change its percentage.