Evaluation of foliar late blight resistance of potato cultivars in northern Baltic conditions

The aim of this study was to evaluate foliar late blight resistance and yield of selected foreign and Estonian potato cultivars, to determine the most promising cultivars for the northern Baltic region. We hypothesized that local cultivars have higher potato late blight (Phytophthora infestans) resistance and yield due to higher blight resistance. Potato late blight observation field trials were carried out in 2012 and 2013 in Einola Farm, Tartu County, Estonia. In both growing seasons, twelve potato cultivars were compared: nine from the Dutch breeding company Agrico and three from the Estonian Crop Research Institute (ECRI). They comprised four early cultivars 'Ranomi', `Esmee', 'Romie' and `Maree, four medium early cultivars 'Toluca', 'Mariska', 'Madeleine' and 'Teele', and four medium late / late cultivars 'Excellency', 'Bellefleur', `Manitou' and 'Anti'. Of these, only two, 'Anti' and 'Toluca', qualified as highly foliar late blight resistant. This research clearly indicates that, despite unfavourable conditions for the pathogen, late blight is able to destroy potato foliage in most of these cultivars before the end of the growing season in northern Baltic conditions. This reflects local genetic heterogeneity of populations of P. infestans, probably associated with the presence of strains adapted to a wide range of humidity conditions. In 2012 that had late blight favourable weather, the cultivar 'Toluca' showed high foliar blight resistance, as it reached the maximum yield compared to other cultivars, which were susceptible or very susceptible to late blight and had drastically reduced yield. However, although the late blight infection was not recorded in the growing season 2013, the cultivar 'Toluca' did not tolerate the dry weather well and its tuber yield remained significantly lower than that in all other cultivars. Additionally, in 2013, a potato early blight (Alternaria solani) outbreak was recorded with the two most susceptible cultivars being the local cultivar 'Teele' and the Dutch cultivar 'Excellency'.