Colorado Seed Potato Certification Data Analysis Shows Mosaic and Blackleg are Major Diseases of Seed Potato and Identifies Tolerant Potato Varieties

Seed potato certification programs aim to limit disease incidence in planting material to levels below a threshold that causes significant losses to seed potato buyers. Records maintained for seed potato certification can be analyzed for trends in seed potato varietal mixture and disease incidences over time. We used logistic regression models to determine effects of year, potato variety, and their interaction on the incidences of potato diseases and disorders based on seed potato certification data collected in Colorado from 2012 to 2016. The effect of seed generation of important varieties on the incidence of common potato diseases was also quantified. Among the documented diseases, mosaic, caused primarily by Potato virus Y, is a persistent problem leading to high percentage of seed lot rejections in both summer and winter inspections, while blackleg, caused by Dickeya spp. and Pectobacterium spp., was a common disease causing summer rejections. The model demonstrated year, potato variety, and their interaction were key factors contributing to incidence of varietal mixture, or one or more potato diseases and disorders. For summer inspections, our models identified 53, 42, and six varieties sensitive to mosaic, blackleg, and leafroll, respectively. There were 17, 15, and six varieties that were tolerant to mosaic, blackleg, and leafroll regardless of pathogen pressures in the environment. For winter inspections, 51 varieties were sensitive to mosaic and three to leafroll, whereas 45 and one were relatively tolerant to mosaic and leafroll. The pattern of seed generation effects of selected potato varieties on mosaic and blackleg incidence was inconsistent across inspection years. In addition, we observed a significant negative correlation between the relative abundance of the green peach aphid, Myzus persicae, and mosaic in winter inspections. Mosaic incidences in summer and leafroll incidences were not influenced by common aphid species captured or total aphids in the valley. These results identify mosaic and blackleg as major causes of seed potato rejections and downgrades, sensitive and tolerant varieties, and provide suggestions for improving integrated crop management practices in Colorado.