Methods for epidemiological research on bacterial blight of rice.
1989
Alvarez A.M. | Teng P.S. | Benedict A.A.
Modern epidemiology relies heavily on quantifying biological phenomena and their relationship with the environment and other factors. Most research to date on rice bacterial blight (BB) caused by Xanthomonas campestris pv. oryzae has been descriptive and ecological. Quantitative analysis of BB epidemics may be done using a "bottom-up" approach through studies on components of infection cycles or by using a "top-down" approach with analysis of disease progress curves (DPCs). The components of the BB infection cycle are primary inoculum source, colonization on host surface, entry into host, symptom development, dissemination, survival in air, deposition, and survival on plant surface, weeds, and nonliving media. BB pathogen populations are measured either as number of cells per unit area or volume, or as number of groups of cells that function collectively to cause infection. Bacterial populations may be characterized by standard bacteriological tests, phage and serological reactivity patterns, fatty acid composition, and isoenzyme analysis. The effects of specific environmental variables on components of the infection cycle are quantified into functional relationships, which collectively constitute a system model and which may be used to explain epidemics in different environments. Many mathematical models are available for quantifying the DPCs of BB. However, fundamental knowledge of how to assess blight symptoms and of the spatial distribution of the pathogen and diseased rice plants is required for accurately interpreting DPCs. Much of this knowledge does not currently exist. Neither does knowledge of the quantitative effects of BB on rice yield.
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