CD-ROM Image Analysis Used in Determining Disease Severity in Dogwoods under Physiological Stress

Abstract

CD-ROM technology, scanners, and image capture software have enabled an alternate approach to determining disease severity. When estimating disease damage, information on disease severity may be as important as information on disease incidence. Disease incidence is the proportion of leaves infected on each tree; disease severity is the number of lesions or amount of tissue damage per tree. The Mielke and Langdon scale was used to determine the incidence of dogwood anthracnose on dogwoods under physiological stress; the CD-ROM system was used to determine the severity of the disease. Dogwood seedlings were exposed to four shade and three water levels for 12 weeks. Leaf images were stored on a photo-CD for image analysis. Water availability at 100% water-holding capacity significantly increased disease severity on dogwood leaves inoculated in vitro. The system allowed detection of a significant effect of water availability on susceptibility of the leaf to dogwood anthracnose that was not detected when incidence of infection was evaluated on a whole-plant basis