Archivio Journal of Plant Pathology

Abstract:

In June 2008, a basal stem failure of a sycamore maple tree (Acer pseudoplatanus) occurred in Turin (Italy). The failed tree did not show any external signs of fungal disease. However, the wood at the point of stem breakage was decayed and permeated by black lines. Isolations from decayed wood samples, performed on potato dextrose agar (PDA), yielded white fungal colonies that later turned greyish-brown producing hyaline, smooth and ovate conidia (5.5-7×2.5-3.5 μm) on tufts of sparsely branched conidiophores. Using a multiplex PCR assay (Nicolotti et al., 2009), the fungal cultures were identified as Kretzschmaria deusta. The features of the decayed wood and the morphological traits of pure cultures were also consistent with this diagnosis. After this finding, 77 maple trees, comprising those adjacent to the failed tree, were surveyed and sampled using the drilling method by Guglielmo et al. (2010). Although no overt signs of K. deusta in- fection were observed, multiplex PCR identified this fungus in five trees, comprising four sycamore maples and a Norway maple (Acer platanoides). Three of these infected trees were very close to the failed one, thus suggesting a clustering of infection. Inci- dence of K. deusta was higher than that of other wood decay fun- gi detected by multiplex PCR. Although K. deusta is known as a threat for the stability of different broadleaf trees in the urban context of northern and central Europe, to our knowledge this is the first report of this pathogen in urban maple trees in Italy.