DISEASE ASSESSMENT OF EARLY BLIGHT IN POTATOES IN SEMIARID ZONES

Five methods of assessing early blight (Alternaria solani) on potatoes were examined using field trials in Israel in 1986 and 1987. One method (Mean Days) was unrepeatable and therefore unsatisfactory; four others were repeatable and discriminated between the 16 cultivars examined. However, when relationships with natural senescence were examined, two of the methods (Best Score and Mean Percent) were highly correlated with it. Of the two methods that reflected the rate of increase in disease symptoms, the maximum increase in percentage cover observed in a 14 day period (Delta) was found to be more effective than the linear regression coefficient for the relationship between percentage disease cover and number of days from planting (Slope).