Field Resistance of American Sycamore ‘Davis’ to Canker Pathogens

Abstract American sycamores ( Platanus occidentalis L.) are found in many ecosystems and planted in urban landscapes worldwide. The trees are highly susceptible to anthracnose and canker pathogens, causing leaf blight and branch dieback. On The Ohio State University campus in Columbus, Ohio, an American sycamore was observed to thrive among many symptomatic sycamores. The healthy tree, subsequently protected as cultivar ‘Davis,’ was vegetatively propagated and tested for field resistance to natural infection of canker pathogens compared to the wildtype. Incidence and severity of leaf necrosis, incidence of dieback, and tree death were evaluated for 2 consecutive seasons. The incidence of leaf necrosis was disconnected from the incidence of dieback and tree mortality, as little to no leaves were produced on the wildtype trees. By the end of the second season, 7 out of 12 wildtype trees were dead, while all 12 ‘Davis’ trees were alive. Several canker pathogens were recovered from both ‘Davis’ and the wildtype, including Apiognomonia platani and Diaporthe eres . The latter had not been previously reported on American sycamore. Pathogenicity tests confirmed that D. eres is indeed pathogenic on sycamores and also that ‘Davis’ is significantly more resistant than wildtype to canker development and should be preferred over the wildtype in the urban landscape.