Resistance to Candidatus Liberibacter Solanacearum (Lso) in the Wild Potato Solanum microdontum

Zebra chip is an increasingly serious disease in commercial potato production globally. Resistance can be pursued by control of the insect vector, the tomato-potato psyllid, Bactericera cockerelli or the bacterial causal agent, Candidatus Liberibacter solanacearum (Lso). Some Lso-infected plants of the wild potato species S. microdontum (mcd) had been observed to have low symptom expression. Thus, we evaluated a representative core collection of 86 individuals from 50 mcd populations in the US Potato Genebank (USPG). Real-time quantitative PCR on tissue from infected leaves was used as a proxy for bacterial titer of Lso. Russet Burbank control had 56% of the MLT of the most susceptible mcd individual. The average for all mcd was 67%, and the lowest, most resistant six mcd individuals were 0%. Repeated testing of those six individuals identified two as most reliably resistant: mcd15B2 from PI 265575 and mcd62B1 from PI 498126. All of these mcd individuals are available from USPG. They should be useful for research and breeding aimed at better understanding and controlling Zebra chip disease.