PATH COEFFICIENT ANALYSIS OF THE EFFECT OF RAINFALL VARIABLES ON THE EPIDEMIOLOGY OF PHYTOPHTHORA BLIGHT OF PEPPER CAUSED BY PHYTOPHTHORA-CAPSICI

Field plots were established in Delray Beach, FL, in the spring and fall of 1984, the spring of 1985, and the fall of 1986 to quantify disease progress and the effect of rainfall and temperature variables on Phytophthora blight of pepper caused by Phytophthora capsici. From point sources of inoculum (diseased plants), the incidence of disease was observed to spread outward over time from the central, primary foci. Disease progress was observed to be influenced by rainfall and the movement of water over the soil and plastic mulch. Path coefficient analysis was conducted to determine which rainfall variables had relatively large, direct, or indirect effects on the incidence and the rate of disease progress without the confounding influences of multicollinearity. The cumulative amount of rainfall had the largest, absolute direct effect on disease progress and was a large component of the indirect effects of the other variables in three of the trials. A cumulative rain intensity index had the largest, absolute direct effect in one trial. The cumulative number of days with rainfall, the cumulative daily average temperature, and chronological time had far lesser effects, indicating their lack of influence on disease progress. The amount of rainfall also had the largest, direct effect on the rate of disease progress when calculated between disease assessment dates and was the largest component of the indirect effects of the other variables in all four trials. The other rainfall and temperature variables had relatively less influence on the rate of disease progress. The average rates of symptom expression were 0.14, 0.14, 0.20, and 0.27 per unit per centimeter of rainfall for the four trials.