Abstract from: Andrade-Piedra, J. L. 2005. Potato late blight: Modification, validation and qualification of the LATEBLIGHT model. Ph. D. thesis. Cornell University, Ithaca, NY. Three publications in peer-review journals about this topic will be available in 2005.

LATEBLIGHT, a mathematical model that simulates the effect of host, environment, and fungicide use on asexual development of Phytophthora infestans on potato foliage was modified, validated, and qualified so that it could be used in the Andes and, eventually, worldwide. The modifications included (i) use of experimentally-measured parameters of lesion growth rate (LGR), sporulation rate (SR), and latent period (LP) of specific potato cultivars and pathogen lineages; (ii) incorporation of improved equations for the effect of temperature on LGR and SR; and (iii) incorporation of temperature-dependent LP. Parameterization of the model was done by measuring LGR, SR, and LP for three Peruvian potato cultivars infected with isolates of a new clonal lineage of P. infestans.

For validation, observed data were from field trials with three potato cultivars in three Peruvian locations in 1999 and 2000 for a total of 12 epidemics. Observed and simulated epidemics were graphically compared using disease progress curves and numerically using the area under the disease progress curve in a confidence interval test, an equivalence test, and an envelope of acceptance test. The level of agreement between observed and simulated epidemics was high and the model was found to be valid according to subjective and objective performance criteria.

Qualification was done by testing the model in a wide range of environments. Observed epidemics from Ecuador, Mexico, Israel, and the USA involving 13 potato cultivars (32 epidemics in total) were compared with model predictions using graphical and statistical tests. The host resistance level for each cultivar was assigned based on general categories reported by local investigators. For eight cultivars, the model predictions were similar to the observed data. For four cultivars, the model predictions overestimated the disease, likely due to inaccurate estimates of host resistance. Model predictions were inconsistent for one cultivar and for one location.

We concluded that LATEBLIGHT can be used in the domain of applicability defined by the range of conditions observed in the field experiments of this study as a research and educational tool. Fungicide treatments were not considered.