Fastidious, phloem-limited bacteria, pathogens of sugar beet

Sugar beet, Europe’s sole sugar source, faces significant threats from two phloem-limited pathogens: ‘Candidatus Arsenophonus phytopathogenicus’ and ‘Candidatus Phytoplasma solani’. These are associated with syndrome “basses richesses” and rubbery taproot disease (RTD), respectively. Surveys across Central Europe revealed a predominance of ‘Ca. P. solani’, including a novel 16SrXII-P subgroup strain in eastern Germany, while ‘Ca. A. phytopathogenicus’ dominated in Western Europe. Genetic analysis showed minimal pathogen diversity within the Pannonian Plain but higher variability in other regions. The cixiid Reptalus quinquecostatuswas confirmed as the vector of the epidemic ‘Ca. P. solani’ strain (tuf-D) detected in the RTD outbreaks, which also increased susceptibility to Macrophomina phaseolina. These findings underscore the need for improved monitoring and management of sugar beet pathogens across Europe.