False positive Ralstonia solanacearum real‐time PCR results in routine potato tuber samples caused by Advenella species: adaptations to avoid these cross‐reactions

Several real‐time PCR tests for the detection of Ralstonia solanacearum have been developed in recent years. Only the RS primer‐probe system, developed by Weller et al., detects all phylotypes of R. solanacearum in one test. The Saxon State Company for Environment and Agriculture (BfUL) has been using this real‐time PCR test since 2012 for routine testing of potato samples for R. solanacearum. Since the introduction of this test in the laboratory, samples were analysed which were suspected to be false positives [as they gave negative results in other standard tests of the European Union (EU) Commission Directive 2006/63/EC]. Advenella kashmirensis was identified as the cause of selected false positive samples. Inclusion of the three other known Advenella species revealed that this genus could be responsible for false positive results. Because of the rising number of these cases over the last years, two different modifications of the original test from Weller et al. were evaluated independently. It was possible to reduce false positive events, caused by Advenella species by 95% in retested potato tuber samples by using a shortened RS‐primer set in the first adaption of the RS primer‐probe system of Weller et al. The combination of the original RS primer‐set, published by Weller et al., with the RSP‐55T MGB‐probe, published recently in Vreeburg et al., in a second adaption, eliminated false positive events completely.