Exploring resistance to Ca. Phytoplasma solani and Ca. Liberibacter solanacearum in potato

Potato (Solanum tuberosum) faces emerging threats from the bacterial vector-borne diseases Zebra Chip and Stolbur, caused by the invasive Candidatus Liberibacter solanacearum and Candidatus Phytoplasma solani, respectively. Identifying resistance sources against these phloem-limited pathogens is particularly challenging, because these bacteria are not culturable, quarantine regulations heavily restrict disease testing, and in potentially resistant plants, it is often unclear whether the defense response targets the bacteria or the insect vector. To address these challenges, we take one puzzle piece at the time. First, we apply an effectoromics approach in wild Solanum genotypes. Subsequently, genotypes that respond to effectors are tested for bacterial resistance by grafting. Ultimately, genotypes that exhibit resistance in the grafting assays undergo disease testing with their insect vectors. So far, we have identified various Solanum genotypes that mount defense responses to effectors of Liberibacter and Phytoplasma. We have successfully established grafting experiments with Phytoplasma in wild Solanum accessions, and screening efforts are ongoing. Our goal is to identify immune receptors against these bacteria that can be introduced into potato cultivars to enhance the resistance against this emerging disease.