Cultivar differences in susceptibility to early blight in starch potato

Potato early blight is a fungal disease mainly caused by the pathogen Alternaria solani, leading to yield losses in starch potato production. Chemical control with synthetic pesticides is the most used method of controlling early blight in Sweden. To reduce fungicide applications as a strategy following Integrated Pest Management (IPM) principles, evaluating the disease severity in different cultivars is important. Currently, there are no early blight resistant potato cultivars or identified resistance genes. The resistance to early blight in potato cultivars is thought to be linked with the maturity rate, and late-maturing cultivars have lower infection rates. This study aimed to evaluate cultivar differences in susceptibility to early blight. Two separate field trials, each ranging over three growth seasons, were performed in southern Sweden. The early blight disease severity rate, tuber and starch yield, leaf fungal biomass (A. solani), and leaf nutrient analysis were evaluated for eight starch potato cultivars presently grown by the Swedish starch potato industry. The results suggest that there are differences in susceptibility among the cultivars, which are not only maturity dependent but also linked to underlying genetic resistance. Cultivar differences in resistance and fertilization must be communicated to the growers to create specific treatment guidelines and reduce pesticide usage and risk of yield loss.