VIEW ARTICLE

Ecology and Epidemiology

Studies in Focus Development: An Optimum for the Dual Dispersal of Plant Pathogens. M. W. Zawolek, Institute for Plant Breeding and Acclimatization, Cereals Department, Zawila 4a, 30-423 Cracow, Poland, and Department of Phytopathology, P.O. Box 8025, 6700 EE Wageningen, The Netherlands, Present address: CIBA-GEIGY, SPHINX Project Office, 37 Kasr El Nil Str., P.O. Box 30 Mohamed Farid, Cairo, Egypt; J. C. Zadoks, Institute for Plant Breeding and Acclimatization, Cereals Department, Zawila 4a, 30-423 Cracow, Poland, and Department of Phytopathology, P.O. Box 8025, 6700 EE Wageningen, The Netherlands. Phytopathology 82:1288-1297. Accepted for publication 25 June 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1288.

Many pests and diseases have two or more dispersal mechanisms, differing in dispersal parameters and relative frequencies. However, published studies all refer to models with a single dispersal mechanism. A new numerical method, based on diffusion theory, allowed simultaneous determination of two dispersal mechanisms. The model was parametrized with data from focus-forming Uredinales and Peronosporales. A form of sensitivity analysis allowed us to study not only the effects of input parameters on output parameters but also the effects of their interactions. These output parameters are the total number of lesions in a finite field and the velocity of focus expansion. Some general rules about the dual dispersal mechanism are ventured. The most important finding is the existence of an optimum value for the partition coefficient, F, the proportion of spores attributed to the short-distance dispersal mechanism, for both output parameters.