First occurence of Candidatus Phytoplasma solani associated with seed potato in Belgium

Potato phytoplasmas are serious phloem-limited disease agents reported in South Eastern Europe, Russia and the Mediterranean region. Since 2006, several outbreaks have also been recorded in Western Europe. These insect-transmitted pathogens reduce tuber quality and cause considerable yield losses. Symptoms on potato plants infected by phytoplasmas include upward rolling of the upper leaves with reddish or purplish discoloration, bud proliferation, shortened internodes, swollen nodes, aerial tubers, wilting and early senescence. Little is known on the epidemiology of potato phytoplasma in Europe, let stand in Belgium.

The objective of the present study was to conduct a survey and identify phytoplasmas associated with seed potato in Belgian fields. Different seed potato varieties from different origins in Flanders (Belgium) were planted on a post control field established at ILVO. During summer 2012, symptomless and symptomatic potato plants, showing leaf purpling and curling, leaf yellowing and aerial tubers, were observed, collected and tested for phytoplasmas.

Total DNA was extracted from leaf veins and tubers by using the CTAB method and kept at -70°C. PCR assays using phytoplasma universal primer pair P1⁄P7 followed by primer pairs R16F2n⁄R16R2 and fU5⁄rU3 were used for detection. Nested PCR assay using primer pairs for tuf gene and 16S rDNA according to the QBank molecular decision scheme for EU regulated phytoplasma was used for identification and sequencing analysis.

PCR amplicons at the expected size were produced among all symptomatic potato samples. No amplification products were obtained from non-symptomatic samples. Sequence analyze of the tuf gene indicated that Stolbur was the only phytoplasma detected in seed potato lots in Flanders.

In this study, we demonstrated that observed aforementioned symptoms on potato were definitely caused by phytoplasma. The genotyping analysis allowed placement of the causal organism within the Candidatus Phytoplasma solani, specifically group 16SrXII-A. More research concerning potato phytoplasma epidemicity, identification of their culprit insect vectors and weed ecological reservoirs is actually ongoing at ILVO. To our knowledge, this is the first documented report of stolbur phytoplasma associated with potato in Belgium.