Common scab trials of potato varieties and advanced selections at three U.S. locations

Common scab (CS), caused by Streptomyces spp., is a soil-borne bacterial disease of potato tubers which may cause superficial, raised, or pitted lesions. The results of screening potato germplasm for severity of CS can be variable, necessitating testing over multiple environments. The purposes of this study were to evaluate advanced germplasm from public potato breeding programs in different regions of the United States for their reaction to CS, estimate broad-sense heritability for resistance, and identify clones with stable resistance. Seventeen to 23 clones per year were evaluated at each of three locations (ID, ME, MN) from 2002 to 2007. After harvest, each tuber was scored for the percent of surface area covered with lesions and the type of lesion. These scores were converted to an area index (AI) and a lesion index (LI). AI, LI, and the arcsine √ proportion scabby tubers (PS) were analyzed as normally distributed responses. There were significant differences among clones for AI in 2 years, LI in 5 years, and PS in 3 years. There were significant clone x location interactions for AI and PS all 6 years, and LI in 5 years. Broad-sense heritability for AI, LI, and PS ranged from 0 to 0.78, 0.49 to 0.90, and 0.30 to 0.80, respectively. Evaluation at multiple sites remains important for characterizing the reaction of potato germplasm to CS.