ASSOCIATION OF XYLELLA FASTIDIOSA, CERATOCYSTIS FIMBRIATA f. PLATANI AND BOTRYOSPHAERIA RHODINA WITH DECLINING SYCAMORE PLANTATIONS IN THE SOUTH-EASTERN USA
KO BRITTONl , T LEININGER2, CJ CHANG3,
and TC HARRINGTON4
1USDA Forest Service, Athens, GA 30602, 2USDA Forest Service, Stoneville MS 38776, 3 Univ. Of Georgia Agric. Expt. Sta., Griff in, GA 30223-1797, 4 Dept. Of Plant Pathology, Iowa State Univ., Ames, IA 50011, USA
Background and objectives
Hardwood fiber is needed for the production of certain paper products. Predicted shortages have led to renewed interest in hardwood plantations as a sustainable system for fiber production. American sycamore (Platanus occidentalis) is a desirable species because of its rapid growth rate and pulping qualities. However, sycamore plantations have for many years been plagued with a mixture of diseases that led to sycamore's disfavor as a plantation species. To determine the cause of sycamore dieback (or decline), we compared the frequency of occurrence of various pathogens in 11 plantations in the southeastern US.
Materials and methods
Declining sycamore plantations age 5-20 were sampled in a wide variety of sites in Aug-Sep, 1997. Symptoms consisted of thin crowns, dieback, and epicormic branching. Scorching of leaf margins was evident in some trees in all locations. In some locations, purple stem lesions extended from the dying crown into the main bole of affected trees. Vascular discoloration was observed beneath these lesions. In other locations, discrete cankers with callus margins were present on trunks and main branches. Leaf petioles were sampled from trees with leaf scorch and from symptomiess trees, and processed for ELISA testing using an AgDia ELISA kit. lsolations for Xylella fastidiosa were performed on a subset of petiole samples, using PW, PD2, or CS20 media, following the method developed by Chang et al. .
Wood chip samples were taken from discolored xylem around cankers, and from branches with dieback. Wood samples were subdivided, for isolation of fungal pathogens. Half were plated on acidified potato dextrose agar, and incubated under fluorescent lights for two weeks. The other half were sandwiched between two carrot slices, wrapped with masking tape, and placed in plastic bags for 10 days. This method was recommended for isolation of Ceratocystis fimbriata f. platani. All wood samples were incubated at about 24°C.
Results and conclusions
Several pathogens were detected in most of the plantations. Positive ELISA tests for X. fastidiosa were obtained from ten of the eleven plantations. lsolations of X. fastidiosa on selective media were conclusive in eight plantations. C. fimbriata was isolated from all four plantations sampled in coastal North Carolina, but not from any of the other plantations. Three of these were coppice plantations. No Botryosphaeria rhodina was isolated from these four sites. However, B. rhodina was isolated from all seven other plantations. The most severely affected plantations were those located in southern Alabama. These had exhibited initial dieback at age 3, and were severely affected when we sampled them, at age 5. Both X. fastidiosa and B. rhodina were isolated from these plantations. Phomopsis sp. and Cephalosporium sp. were isolated in low frequency from four and two plantations, respectively.
These data suggest a complex of organisms are associated with sycamore dieback or decline in the southeastern United States. Further research is needed to determine whether these pathogens act alone or in concert, and which are most important in the disease etiology.
1. Chang, CJ, Robacker, CD, and Lane, RP. 1 990. Can. J. Pl. Pathol. 12, 405-408.