©2023 International Society of Arboriculture 170 Farinas Simmt et al: Field Resistance of American Sycamore ‘Davis’ to Canker Pathogens Arboriculture & Urban Forestry 2023. 49(4):170–178 https://doi.org/10.48044/jauf.2023.013 anthracnose include slow leaf development in the spring, leaf blight with characteristic angular-shaped necrotic lesions along the veins, stem, and twig can- kers (twig blight), and irregular branching patterns due to terminal bud death (bud blight). Despite the impact that the disease has on sycamores, studying the pathogen-host system has proven challenging. Various authors have reported having diffi culties infecting London planes reliably with conidia and ascospores of A. platani (Milne and Hudson 1987). In their experiment, Milne and Hudson (1987) report that only 10% of young and wounded leaves devel- oped symptoms. To overcome this challenge, other studies relied on natural infection and achieved up to 80% infection rate (Milne and Hudson 1987). In addition to anthracnose, several causal agents of leaf spot and canker diseases, such as Diaporthe eres Nitschke, D. medusina (Fr.) Sacc, and Diaporthe scabra Nitschke, have also been reported on London planes (Wehmeyer 1933; Grasso et al. 2012). How- ever, Gomes et al. (2013) report that D. scabra iso- lated from London plane was misidentifi ed and INTRODUCTION Platanus occidentalis L., American sycamore, is an endemic, deciduous tree species with primary distri- bution in Eastern North America. The trees play an important ecological role as dominant riparian spe- cies but are also a valuable timber resource (Sullivan 1994). Thanks to the striking white bark that develops higher on the bole as they age, they are also exten- sively used as ornamental trees in landscapes world- wide. However, this tree species is highly susceptible to disfi guration by anthracnose, leaf spot, and canker diseases. Thus, any American sycamore resistance to these ailments is highly valuable. The causal agent of sycamore anthracnose, the ascomycete Apiognomonia platani (Lév.) L. Lom- bard comb. nov. (2021)[syn. Apiognomonia veneta, Discula platani] was fi rst described on P. occidentalis in 1976 (Milne and Hudson 1987). Other species, such as Platanus hybrida Brot. or London plane (Pla- tanus × acerifolia), are mostly planted in urban areas and are highly susceptible to anthracnose as well (Milne and Hudson 1987). The main symptoms of Field Resistance of American Sycamore ‘Davis’ to Canker Pathogens By Dr. Coralie Farinas Simmt, Dr. Davis Sydnor, Elizabeth L. White, Alexis Wooten, Dr. Francesca Peduto Hand, and Dr. Pierluigi (Enrico) Bonello 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 pro- tected as cultivar ‘Davis,’ was vegetatively propagated and tested for fi eld 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 confi rmed that D. eres is indeed pathogenic on sycamores and also that ‘Davis’ is signifi cantly more resistant than wildtype to canker development and should be preferred over the wildtype in the urban landscape. Keywords. Anthracnose; Apiognomia platani; Canker; Diaporthe eres; Disease Resistance; Sycamore. Scientifi c Journal of the International Society of Arboriculture
July 2023
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