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Simulating potato late blight in the highland tropics

Abstract:

A potato (Solanum tuberosum L.) late blight (LB) simulation model was validated near Quito, Ecuador, at three sites and over two growing seasons. Two varieties differing in resistance to Phytophthora infestans (Mont.) de Bary, the causal agent of LB, were grown at each site. Data taken from each site included hourly temperature and relative humidity and daily rainfall. Using weather data from each site, the model simulated disease severity for each variety. Resistance parameters for the model were taken from measurements made on the Peruvian varieties Amarilis-INIA (resistant) and Tomasa Tito Condemayta (susceptible). At each site, the model simulated realistic differences between susceptible and resistant varieties. However, for the experiments conducted where average daily temperatures were low (less than 14 C), the model underestimated disease severity. These temperatures are characteristic of the principal potato growing area of Ecuador. The most accurate simulation occurred at the Tola site in both seasons, where average daily temperatures are above 14 C. Overall, temperature was inversely related to the predictive capability of the model. Late blight is a major constraint to potato production worldwide. The disease is especially damaging in the tropical highlands of Latin America, Asia, and Africa, where it can be controlled only by routine applications of fungicides, sometimes in conjunction with moderate levels of host plant resistance (Forbes and Jarvis, 1994; Haverkort, 1990). For many poor farmers, however, the disease is not controlled, losses are heavy, and crop abandonment is not uncommon.