Shoaei, Zahra

ABSTRACT Phytoplasmas were detected in potato tubers and sugar beet roots in neighbouring fields in Southern Germany using quantitative PCR. Infected potato plants showed phytoplasma‐associated symptoms including yellowing, upward leaf rolling, aerial tubers and early senescence. Sugar beet plants showed similar symptoms to those of syndrome ‘basses richesses’ (SBR) disease, including proliferation, yellowing and necrosis of older leaves. The genetic diversity of the phytoplasmas in the symptomatic potato and sugar beet plants was investigated through sequence analysis of 16S rRNA and stamp , vmp1 , tuf and secY genes. The RFLP profiles and sequences of 16S rRNA were identical among all the sugar beet‐positive samples and aligned with subgroup 16SrXII‐P, whereas the potato phytoplasma strains were identified as belonging to subgroup 16SrXII‐A. Sequence analysis of the non‐ribosomal genes showed that the potato strains belonged to the b1 group of the tuf gene, the V4 and V17 groups of the vmp1 gene and the secY3 and secY4 groups of the secY gene. However, the sugar beet strain was clearly distinct from the potato strains. Together with strain 916/22 from sugar beet in eastern Germany, they formed a new group of tuf , secY , vmp and stamp genes. RFLP assays and multilocus sequence analysis of non‐ribosomal genes of the phytoplasma strains confirmed that the potato phytoplasma strains were molecularly different from the sugar beet phytoplasma strains. In addition, this is the first report on the multilocus sequence analysis of ‘ Candidatus Phytoplasma solani’ strains in potato plants in Germany, suggesting differences in source plants other than sugar beet or interactions with insect vectors specific to each crop.

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.