Author : Sopialena

Summary : The epidemiology of leaf spot of maize caused by Bipolaris maydis Nisik. and Miy. was studied. Weather factors from all over Indonesia and regions in East Kalimantan were correlated to disease prevalence, whose development was significantly influenced by temperature, relative humidity, and rainfall. The effect of host resistance was studied in Part II. Resistant cultivars had a longer incubation period, smaller lesion size and lower disease severity. Disease development and hence infection rate was higher in susceptible cultivars: that of Pioneer 3012 was twice that of the Composite 5 and thrice that of Hibrida CP I-2. An experimental study of leaf spot development in Lempake and Purwajaya in East Kalimantan showed significant differences, with infection rate and average disease severity significantly higher in national compared to local cultivars. The effect of aggressiveness on disease development was studied under laboratory and field conditions using isolates collected from around East Kalimantan. The Malinau isolate was the most aggressive, that from Tarakan the least aggressive. There was a high correlation between disease severity and yield loss. the area-under-the disease-progress-curve model explained the relationship between disease and yield loss with the regression model Y=8.885 + 0.675 X (R2 = 0.827).