Use of Crop Growth-Models to Predict the Effects of Disease

Abstract

The ultimate goals of the agricultural plant sciences are to increase the yield and improve the quality of domesticated crops as well as the economic efficiency of farming. To achieve these goals plant scientists must first identify the factors that limit yield and lower quality and then quantitate the magnitude of their effects. Crop cultivars rarely or never produce to their full genetic potential since conditions are rarely or never perfectly ideal for plant growth. The yield-limiting factors include physical environmental variables, chemical variables, and biological variables, especially pests. This review is particularly concerned with the role of plant diseases in limiting crop yield and quality. Determining the role that a specific pathogen plays in limiting yield requires quantitative knowledge of the interaction between host and pathogen. It is also necessary to understand how the host-pathogen interaction itself is influenced by abiotic and other biotic factors, some of which may also limit crop growth directly. The objective of this chapter is to review models that have been developed to quantify the interaction between host crop and pathogen. My thesis is that crop growth-based epidemic and yield-loss models are superior to models that do not explicitly model crop growth. Specifically, a crop growth-based model is required to realistically quantify disease progression, as opposed to the progression of signs or symptoms of disease. This is important in understand­ ing yield loss if the relationship between visible disease and the degree of abnormal plant function induced by the pathogen is nonlinear. Such quantita­ tion is also important if the diseased plant, because of abnormal function,