Model analysis of the effect of initial inoculum density on potato late blight epidemics and potato yield: Implications for modeling atmospheric transport

A spatiotemporal/integro-difference equation model of the potato late blight pathosystem was developed and utilized to investigate acceptable margins of error in predictions of the dispersal of Phytophthora infestans spores. This was achieved through a study of the yield response of potato cultivars to initial inoculum densities that varied six orders of magnitude, where initial inoculum densities were considered to be predictions of spore fluxes arriving at a target crop. The impact of initial inoculum density on yield was investigated for 4 hypothetical cultivars under 4 fungicide regimes, making a total of 16 scenarios. Ten years of historical weather data were used to provide a realistic range of conditions for crop growth and potato late blight development. The results of the simulation experiments facilitated a classification of the 16 scenarios into 3 groups: high, intermediate and low level of protection against potato late blight. The magnitude of the yield response to changes in initial inoculum density within each group clearly portrayed that accuracy in the predictions of a spore dispersal model is critical only in some situations. In the group where the level of protection was relatively high, the yield response to changes in initial inoculum densities was minimal. In contrast, where the level of protection was relatively low, crops were so vulnerable that major yield losses resulted from very low inoculum densities, implying that an unrealistic level of accuracy would be required of a dispersal model. Where the level of protection was intermediate, yield decreases caused by a change in inoculum density of one order of magnitude varied between 1.6 and 2.8 ton (DM) ha super(-1). This suggests that the future role of dispersal modeling in potato late blight control lies in the use of state-of-the-art dispersal models from meteorological sciences, focused on situations where the level of protection can be considered as intermediate; here, there is potential to reduce the fungicide input of potato late blight control through a more accurate quantification of infection pressure. The calculation of dynamic, as opposed to fixed, risk-zones around target crops is proposed as one potential use of such models.