Integrating cultivar resistance into the TOMCAST model to control early blight of potato, caused by Alternaria solani

Field experiments were carried out in 2016 and 2017 to integrate cultivar resistance into the TOMCAST model to control early blight on potato crops. Four potato cultivars (cvs. Agata, Sava, Oleva and Kuras), which varied for their level of resistance to early blight were used for the experiments. Fungicide (fungicide schedule) was applied as follows: an untreated; a standard treatment, in which fungicide application started at 50% row closure; and three different TOMCAST (tomato forecaster) treatments, in which fungicide application started at 330 physiological days (P-days) and subsequent sprayings were done at either 15, 20 or 25 TOMCAST threshold according to temperature and leaf wetness. The relative area under the disease progress curve (rAUDPC), rate of infection and final severity of early blight were used to quantify the intensity of early blight on the potato crops. Moreover, disease progress curves (DPCs) were constructed to compare the development of early blight on the cultivars. Analysis of the DPCs, rAUDPC, rate of infection and final severity of early blight showed that both fungicide application and cultivar resistance were important in suppressing the development of early blight. Fungicide application significantly reduced the rAUDPC, rate of infection and final severity of early blight on the potato crops in the treated plots compared to the untreated plots. TOMCAST-15 was the most effective TOMCAST threshold for controlling early blight on all the tested cultivars. For cv. Kuras, with a high level of resistance, the control of early blight by the TOMCAST thresholds was very good and comparable to the standard treatment. Therefore, we concluded that lower TOMCAST thresholds should be used for susceptible cultivars. However, for cultivars with a good level of resistance, a higher TOMCAST threshold could be used to control early blight effectively.