Molecular detection and multilocus sequence analysis of Candidatus Phytoplasma solani-related strains infecting potato and sugar beet plants in Southern Germany
Abstract
Syndrome ‘basses richesses’ (SBR) disease in sugar beet caused by two phloem-limited pathogens, 'Candidatus Arsenophonus phytopathogenicus' and 'Candidatus Phytoplasma solani' is a fastspreading disease in Central Europe. The planthopper vector, Pentastiridius leporinus (Cixiidae), has recently expanded its host range to potato in Germany. However, the genetic diversity of 'Ca P. solani' in potato and possible association to SBR phytoplasma is unknown. In this study we charachterized ‘Ca. P. solani’ infecting sugar beet and potato plants in close distance fields in Southern Germany. Initially, the pathogen was detected in the potato tubers (18.7%) and sugar beet roots (60%) using TaqMan Real-Time PCR. Then, the sequences of 16S rRNA and other informative genes (stamp, vmp1, tuf and secY) were analysed in a number of infected potato and sugar beet plants. The phytoplasma strain infecting sugar beet in Southern Germany was classified into 16SrXII-P subgroup, a novel subgroup recently reported from sugar beet in Eastern Germany. While, the potato related strains were close to 16SrXII-A, which is a common subgroup for potato stolbur reported in Europe. The multilocus sequence analysis (MLSA) of non-ribosomal genes of the phytoplasma strains showed that the potato strain is clearly different from the sugar beet associated strain in this region. The presence and prevalence of 16SrXII-P in sugar beet in Southern and Eastern Germany suggests that this subgroup is dominant in sugar beet in Germany. In addition, this study elucidates for the first time, the genetic diversity of ‘Ca. P. solani’ strains in potato in Germany with a possible different source rather than sugar beet. Further investigation is required to investigate genetic variation of ‘Ca. P. solani’ in all sugar beet and potato-growing regions including weeds host in Central Europe to better understand the epidemiology of both sugar beet SBR and potato stolbur disease.