Genetic diversity of ‘<em>Candidatus</em> Phytoplasma mali’ strains in Poland

Abstract

During 2010-2013, samples from 267 apple trees growing in six regions of Poland were tested for phytoplasma presence. ‘Candidatus Phytoplasma mali’ was detected in 17 samples from phloem tissue of apple shoots showing typical apple proliferation symptoms. Molecular characterization of these strains was conducted using PCR-RFLP and sequence analyses of three regions: ribosomal DNA, ribosomal protein and non-ribosomal DNA fragment including nitroreductase and rhodanese-like protein genes. Fragments of 16S rDNA plus 16S-23S spacer region from the ‘Ca. P. mali’ strains showed two restriction profiles: P-I and P-II when digested with HpaII enzyme. Moreover, based on results of nitroreductase and rhodanese-like protein genes, these phytoplasmas were grouped into two subtypes: AP-15 and AT-1. The majority of the ‘Ca. P. mali’ strains was classified to the AP-15 subtype. Two strains were grouped to the AT-1 subtype and another showed both AP-15 and AT-1 profiles. Based on results of analysis of rpl22 and rps3 ribosomal protein genes, most of the ‘Ca. P. mali’ strains were identified as belonging to rpX-A. Only one strain was affiliated to rpX-B subgroup.