A MODEL BASED ON TEMPERATURE AND LEAF WETNESS DURATION FOR ESTABLISHMENT OF ALTERNARIA LEAF-BLIGHT OF MUSKMELON

We inoculated muskmelon leaves with a conidial suspension of Alternaria cucumerina and subjected the leaves to various controlled environments to determine the influence of temperature and leaf witness duration on disease establishment. Disease severity, as measured by a "number of lesion area equivalents" method, increased with increasing wetness duration (2-24 h) at all temperatures tested (12-30 C). The optimum temperature was 18 C, and at least 8 h of leaf wetness were required for significant disease establishment at temperatures of 15-21 C. Analysis of variance with orthogonal polynomial contrasts and also regression analysis were used to determine the functional relationship between disease severity and temperature and leaf wetness duration. The resulting polynomial response surface provided a close fit to the observed data.