Detection, Identification, and Characterization of Phytoplasmas Infecting Apple and Pear Trees in Belarus

In Samochvalovichi, Belarus, apple and pear tree root samples were examined for the presence of phytoplasmas using a universal 16S rDNA-based PCR assay. Out of 27 tested apple trees, 23 were found to be infected by 'Candidatus Phytoplasma mali' and 46 out of 58 pear trees were positive for the presence of 'Ca. P. pyri.' Species were identified by sequence analysis of the 16S rDNA amplicons. The molecular diversity of the phytoplasma isolates was examined by analysis of an hflB gene using single-strand conformation polymorphism (SSCP) and sequence analysis. Therefore hflB gene amplicons from 'Ca. P. mali' and 'Ca. P. pyri' accessions were cloned after amplification. Screening of 640 cloned hflB fragments by SSCP analysis revealed the presence of eight different profiles for 'Ca. P. mali' and 12 different profiles for 'Ca. P. pyri.' The variants were sequenced and compared in multiple alignments. The nucleic acid homology among the hflB gene fragments ranged between 95.4 and 100.0% and 81.3 to 100.0% for 'Ca. P. mali' and 'Ca. P. pyri,' respectively, indicating a high genetic variability within the species. This is the first report on the occurrence of 'Ca. P. mali' and 'Ca. P. pyri' in Belarusian apple and pear trees and their molecular diversity.