TOWARDS A MECHANISTIC MODEL FOR THE VERTICILLIUM-DAHLIAE POTATO SYSTEM

Development of Verticillium dahliae in potato was modelled by coupling a Verticillium subroutine to an existing potato crop growth model, us ing mainly biologically meaningful and measurable parameters. The mode l, written in FORTRAN77, describes disease development in single plant s. Stem base infection is modelled as a stochastic process. The averag e effect on the crop is calculated by taking the average of model reru ns. The parameters of the potato crop growth model were calibrated in advance of those of the Verticillium subroutine. By doing so, correcti ons can be made for lack of fit in the potato growth model. Calibratio n of the Verticillium subroutine was performed using experimental fiel d data of two years at two microsclerotial density levels. The results of the calibration procedure of the Verticillium subroutine improved strongly when the results of runs of both microsclerotial densities we re expressed in one combined goodness of fit value. Simulation of root infection and incidence of stem colonization by V. dahliae were in li ne with experimental data. However, deviances from data from the liter ature at inoculum densities which were not used in the calibration pro cedure indicate that calibration has to be performed using more field data and also incorporating more parameters like those describing fung al dynamics. Optimal runs were obtained at pathozones of c. 30 mum, wh ich may indicate that infections occur only when a microsclerotium is very close to the root.