Epidemiological Studies of Northern Corn Leaf Blight on Corn Inbreds: Loss Assessment and Disease Modeling

Abstract

Inbred lines of maize (Zea mays L.) generally have lower tolerance to stress (e.g. disease) and yield less than hybrids. Inbreds are grown to produce hybrid seed and are intensively managed because of the need to control pollen and fungicidal control of disease on inbreds is economically feasible. Little is known, however, of the exact quantitative relationship between yields of inbreds in seed production and disease, or the possible interaction between defoliation due to detasseling and disease. Northern corn left blight (NCLB), caused by Exserohilum turcicum, an important disease of maize, has provided a model system for evaluating the relationships between disease and components of yields of inbreds. The effects on yields of two detasseling methods and the efficacy of a new fungicide, propiconazole, for NCLB control were also investigated. Data from these studies were used to develop a simulation model to help students conceptualize disease effects on corn yields and management effects on disease and yields. In three inbreds studied, total yields were inversely proportional to areas under the disease progress curves. NCLB also was found to decrease number of kernels per ear and 200-kernel weights in a highly susceptible inbred. Higher disease levels also decreased kernel size, though had no effect on seed germinability. Yields were reduced an average of 9.6% with cutting and 1.0% with pulling tassels from female plants. Numbers of ears per plant, numbers of kernels per ear, and 200-kernel weight tended to be least from plants that had been detasseled by cutting. The effects of detasseling on yields were additive to effects of NCLB on yields. Propiconazole was observed to slow E. turcicum mycelial growth in vitro and NCLB lesion expansion in vivo, but had no effect on germination of conidia or lesion establishment. Data collected in these studies were used to develop a simulation model of disease development, which was incorporated into a corn growth model. The resulting simulation, CORN-Ill, allows exploration of the effects of crop resistance, pathogen fitness, and fungicide application on epidemics and crop yields.