First detection of Arsenophonus in potato crop in Switzerland: a threat for the processing industry?

The phloem-restricted phytopathogenic bacterium Candidatus Arsenophonus phytopathogenicus (Ap) causes the “syndrome basses richesses” (SBR), which has recently emerged as a major burden for sugar beets in several countries of Western Europe. Here, we report the first identification of Ap and its planthopper vector Pentastiridius leporinus in potato fields in Switzerland in 2023. The bacterium was detected in potato plants and tubers exhibiting phytoplasma-like symptoms and collected from cantons currently experiencing SBR outbreaks. Although our analyses indicate the absence of the Stolbur phytoplasma, the pathogenicity of Ap in potato remains unclear, a fortiori in the context of the poor phytosanitary status of crops in Switzerland in 2023. In infected tubers, we show that Ap can be detected after dormancy from the stem end to the emerging sprouts with decreasing titers. Importantly, Ap might induce threadlike sprouts and the browning of the flesh upon frying, raising strong concerns for varieties marketed for chips production. Altogether, our results align with recent studies performed in Germany, highlighting the host shift of Ap and its vector from sugar beet to potato crops. Our data should raise awareness in other European countries where the presence of the bacterium has been recently described.