Interrelations of Root Growth Dynamics to Epidemiology of Root-Invading Fungi

The field of epidemiology of both airborne and soilborne diseases has ad­ vanced rapidly over the past few decades. A large body of experimental data and their theoretical interpretation has been accumulated for the influence of a large number of environmental/biological variables on disease develop­ ment (68, 8 1). Among this body of data and theory, disease progress curves for foliar diseases are well represented (68, 8 1). As has been amply demon­ strated with foliar diseases, an understanding of variables that drive a disease progress curve is very useful in conceptualizing the process of disease development in populations and in developing predictive models helpful in making disease management decisions (4, 33, 34, 68, 8 1). With the diseases induced by soilborne pathogens, disease progress curves have received only limited attention and theoretical interpretations or predic­ tions have been derived primarily from theory developed for foliar diseases (68, 8 1). The much-reduced need, from a disease management point of view, for day-to-day prediction of disease progress with diseases induced by soil­ borne pathogens may be largely responsible for this deficiency. Root growth is an important component in the progress of diseases induced by soilborne pathogens. This concept has long been recognized (35) and would be disputed by few, if any, pathologists. Yet little work has been done to quantitate and refine this concept beyond its recognition level. I intend to address this topic, presenting its current status and some theoreti-