Laboratory Assays Used to Rank Potato Cultivar Tolerance to Blackleg Showed That Tuber Vacuum Infiltration Results Correlate With Field Observations.

Seed potato certification data collected in Colorado from 2012 to 2016 was used to rank potato cultivar tolerance to blackleg. Five cultivars with different tolerance levels to blackleg ('Chipeta' ≈ 'Alegria' ≈ 'Lamoka' < 'Classic Russet' < 'Yukon Gem') were tested to determine whether we could validate field data with laboratory assays. A strain isolated from Colorado, Pectobacterium atrosepticum CW1-4, and the P. atrosepticum type strain, 33260, were used to inoculate plants through vacuum infiltration of tubers or stem inoculation. Disease was assessed with time-lapse video and by measuring lesion length and disease incidence. After vacuum infiltration of tubers with P. atrosepticum CW1-4 and 33260, cultivars varied in tolerance to soft rot ('Lamoka' < 'Classic Russet' < 'Alegria' ≈ 'Yukon Gem' < 'Chipeta'). Blackleg tolerance of the five cultivars also varied after vacuum infiltration ('Lamoka' < 'Alegria' ≈ 'Chipeta' < 'Classic Russet' ≈ 'Yukon Gem'). All cultivars were susceptible after stem inoculation with either strain. In this assay, 'Chipeta' had the longest lesions, and 'Lamoka' had the smallest lesions. Time-lapse video was used to assess 'Classic Russet' and 'Yukon Gem.' 'Yukon Gem' developed disease symptoms faster than 'Classic Russet,' but the difference was not significant. These results indicate that relative susceptibility of the five cultivars to P. atrosepticum depends on the assay used and that laboratory and greenhouse results differed from field observations.