CHARACTERIZATION OF THE VIRUS X TEMPERATURE INTERACTION IN SECONDARILY INFECTED POTATO PLANTS USING EPIVIT

The model EPIVIT, designed for contact- and aphid-transmitted viruses of tuber crops, simulates the percentage of infected tubers harvested from a potato field. It includes a module for tuber infection of plant s with a tuberborne (secondary) infection (efficiency of autoinfection ). This module postulates a monomolecular function for the relation be tween the efficiency of autoinfection and developmental heat, providin g a theoretical basis for understanding how an infectious, systemic vi rus and the environment, represented by temperature, are interacting. The module was calibrated with temperature and autoinfection data obta ined with the modern potato cultivar Yungay (Solanum tuberosum ssp, tu berosum X S. tuberosum ssp. andigena) in five contrasting environments in Peru. Model estimates for potato X potexvirus (PVX), Andean potato mottle comovirus (APMV), potato Y potyvirus (PVY), or potato leafroll luteovirus (PLRV) were obtained. They were more accurate when tempera ture-sensitive growth rates were used for heat accumulation than with constant accumulation rates. The bell-shaped relationships obtained be tween heat accumulation rates and apparent temperature differed for ea ch virus, with optimum heat accumulation rates at 28 degrees C for PVY , and between 18 and 28 degrees C, 20 and 25 degrees C, and 23 and 28 degrees C for PLRV, PVX, and APMV, respectively. With PLRV and PVY dat a, high precision levels (P < 0.05) were only obtained when the parame ter trigger developmental heat was included. This parameter represents a threshold amount of developmental heat accumulated any time tempera ture fluctuates into the range between developmental cardinal temperat ures, before heat becomes effective for the efficiency of autoinfectio n. This calibration supports EPIVIT's assumptions regarding the influe nce of temperature on virus behavior in the host plant. With complete verification of this model component, validation is still needed for f inal confirmation of the model, as well as an elucidation of the biolo gical mechanisms that underlie efficiency of autoinfection and virus b ehavior at different temperatures by analytical research.