Superior resistance to Phytophthora infestans in new pre-breeding potato clones under different nitrogen fertilisation regimes used in organic agriculture

Late blight caused by Phytophthora infestans is the most devastating disease for cultivated potatoes, causing considerable financial loss annually due to loss of yield and costs of fungicide applications. For organic farming especially, the strict limitations on the use of fungicides makes research necessary to investigate factors that influence disease severity. Therefore, effects of nitrogen fertiliser rates on leaf and tuber blight in organically grown potato cultivars and pre-breeding clones were evaluated in the present study. It was found that the foliage of the pre-breeding clones was little, or not at all, affected by P. infestans, irrespectively of the nitrogen application rate, while the cultivars reacted differently with mild to strong late blight symptoms. Only some of the clones and cultivars showed increased infection of tubers at the higher nitrogen application rates, whilst most showed no significant differences between the N rates. Overall, the present study showed that the use of new resistant cultivars could be a suitable approach to reduce late blight in organic farming, where soil nitrogen levels may vary due to the use of different forms of nutrient inputs with varying mineralisation rates.