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.