Geographic Variation in Disease Susceptibility of American Sycamore

Leaf scorch, top dieback, and lethal bole cankers were found in two progeny tests of sycamore in Mississippi. Both tests indicated that southern seed sources are more disease resistant than northern seed sources and that some progenies within seed source have even greater resistance. Although eight organisms associated with one or more of the disease symptoms were identified, determination of the primary organism causing lethal cankers will require further research. American sycamore (Platanus occidentalis L.) has generally had few lethal disease problems. Anthracnose, caused by Gnomonia veneta (Sacc. and Speg.) Kleb., has been reported (Waterman 1924, Himelick 1961, Neely and Himelick 1963), as have canker diseases (Mook 1940, Walter 1946, Thompson 1951, McAlpine 1961, Filer 1969) and top dieback (Thompson 1951, Filer 1969), but losses have been minor. In recent years, however, a potentially serious disease of sycamore involving leaf scorch, dead branches, top dieback, long, narrow lethal cankers extending from the die back area to the base of the tree, orange discoloration of the inner bark, water sprout formation on the lower trunk, and death of the tree after one to ten years, has occurred in Illinois and adjacent states and has been attributed to attacks by various organisms on environmentally stressed trees (Ricketts 1975). In the South, where extensive plantations of sycamore have now been established, a 1973 survey of 26 sycamore plantations in Tennessee, Mississippi, Louisiana, and Alabama revealed trees with symptoms of leaf scorch, top dieback, and lethal bole cankers in four bottomland plantations (Filer et al. 1975). We are reporting variation in the incidence of an array of disease symptoms in two progeny tests in Mississippi. Both tests involve openpollinated progeny of random trees from natural stands of sycamore. The symptoms appeared to be identical to those in the Midwest described SOUTHERN JOURNAL OF APPLIED FORESTRY by Ricketts (1975). However, disease development was much more rapid.