Alternaria Leaf Spot Caused by Species: An Emerging Problem on Ornamental Plants in Italy.

Serious outbreaks of Alternaria leaf spot and plant decay have recently been recorded on several ornamental plants in the Biella Province (Northern Italy). Twenty-two fungal isolates were obtained from infected plant tissues from 13 ornamental hosts. All the isolates were identified morphologically as small-spored species. Multilocus sequence typing, carried out by means of ITS, , , , , and OPA10-2, assigned 19 isolates as , two isolates as belonging to the species complex, and one isolate as an unknown sp. Haplotype analyses of ornamental and reference isolates from 12 countries identified 14 OPA10-2 and 11 haplotypes showing a relatively high haplotype diversity. A lack of host specialization or geographic distribution was observed. The host range of the studied isolates expanded in cross-pathogenicity assays, and more aggressiveness was frequently observed on the experimental plants than on the host plants from which the fungal isolates were originally isolated. High disease severity, population expansion, intraspecies diversity, and increased range of experimental hosts were seen in the emergence of Alternaria disease on ornamentals. More epidemiological and molecular studies should be performed to better understand these diseases, taking into consideration factors such as seed transmission and ongoing climate changes.