Analysis of Epidemiological Components in Yield Loss Assessment

Abstract

Plant disease epidemics are multicomponent systems resulting from the dynamic interaction between pathogen populations, host populations, and the physical environment, often influenced by man’s activities (Kranz 1974). Epidemics, like most ecosystem phenomena, possess a hierarchical property which reflects the many levels of complexity in biological organization. Plant disease epidemics have commonly been analyzed from a “top-down” approach using the disease progress curve as a starting level, or a “bottom-up” approach using monocyclic processes as the starting level (Teng 1985 a). Regardless of the approach used, it is generally accepted that the dynamics of epidemics can only be understood by the use of quantitative techniques, foremost of which is modeling. Many models have been published which describe the disease progress curve or alternatively, simulate the effect of environment on pathogen-host interactions. The top-down or bottom-up approaches for studying epidemics are also reflected in studies of disease effects on host plants, in particular, the disease effects which result in yield loss. Assessment of yield/crop losses would be impossible without a means to realistically quantify the dynamics of epidemics.