Effects of light intensity, leaf temperature, and tree aspect on Discula lesion enlargement rates and acervuli production

Field studies were conducted at Lookout Mountain and Knoxville, Tennessee in 1990-91 to determine the effects of light intensity, leaf temperature, and tree aspect on Discula destructiva acervuli production, and lesion enlargement rates. Higher leaf temperatures were associated with higher light intensities in both sun and shade. Leaves on the east side of trees had higher leaf temperatures and light intensities in the morning. The diameter of the anthracnose lesions increased faster in the spring for both the sunny and shady plots. Most lesions on foliage in the sun had purple-rims whereas necrotic lesions were more prevalent on foliage in the shady plots. Necrotic lesions were more likely than purple-rimmed lesions to contain acervuli and have D. destructiva conidia present when the fungus was allowed to sporulate in moist chambers. The rates of lesion enlargement in shady compared to sunny plots at Lookout Mountain in the second experiment were significantly influenced by light intensity and leaf temperature as determined by covariate analysis.