Image Analysis and Visual Estimates for Evaluating Disease Reactions of Corn to Fusarium Stalk Rot. LAURA R. TODD, Department of Plant Pathology, University of Minnesota, St. Paul 55108. THOR KOMMEDAHL, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 78:876-878. Accepted for publication 13 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0876.

Two field-grown hybrids were evaluated in three tests (1987-1989) for reaction to the stalk rot fungi Fusarium moniliforme, F. graminearum, and F. proliferatum, using a visual rating scale (0-4) and image analysis (0 100%). Both rating methods indicated that hybrid W153R ? A619 had more stalk discoloration than A632 x A619 when inoculated with any of the three Fusarium species. The difference between hybrids was greater when an image analyzer was used. Significant differences (P = 0.05) between the disease reactions caused by the three pathogens were found among ratings made with the image analyzer in all 3 yr of testing. F. moniliforme, compared with the other Fusarium spp., caused significantly more (P = 0.05) stalk discoloration in the 1987 and 1988 tests when measured by the image analyzer. Significant differences among discoloration caused by Fusarium species were found only in the 1988 test using the visual rating scale. The image analyzer provides a more precise means of evaluating corn for susceptibility to Fusarium stalk rot as compared to visual ratings.