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Response of Fusarium solani to Constant and Fluctuating Temperatures and Its Relationship to Fusarium Canker of Sugar Maple. T. Craig Weidensaul, Formerly Research Assistant, Department of Plant Pathology, currently Head, Laboratory for Environmental Studies and Associate Professor of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; Francis A. Wood, Formerly Research Associate, Center for Air Environment Studies, and Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, currently Professor and Head, Department of Plant Pathology, University of Minnesota, St. Paul 55121. Phytopathology 64:1018-1024. Accepted for publication 23 February 1974. DOI: 10.1094/Phyto-64-1018.

Fusarium solani, a cause of an annual canker of sugar maple, develops during the dormant season. Studies of the temp response of the organism indicated that the threshold for linear growth was about 6 C, and that an average of 100 effective day-degrees was necessary for 20 mm of linear mycelial growth in a fluctuating temp regime similar to that observed in nature. Growth was greater in a fluctuating temp regime than at the constant median about which temp fluctuated. During the spring and fall of 1968, temp beneath the bark of sugar maples was recorded at three heights on four tree faces. Approximately 600 effective day-degrees were available for fungus growth during this period. Although there were differences in temp among faces and heights, there were no differences in total effective day-degrees during this period. When the rate of mycelial growth in vitro was extrapolated for 600 day-degrees, the amount of linear growth approximated the average length of cankers observed in nature. Canker incidence has been reported to be greater on some tree faces than on others and to vary inversely with height. While the results indicate temp is limiting, it is not the only factor responsible for distribution of cankers on tree stems.