Identification and Pathogenicity of Botryosphaeriaceae, Colletotrichum, and Phytophthora Species Associated with Avocado Diseases in Italy

With the rapid expansion of avocado cultivation in southern Italy, growers have had to deal with the emergence of new diseases often caused by invasive and polyphagous pathogens responsible for leaf spot, branch cankers, dieback and fruit and root rot. Given the severity of these emerging diseases, a study was conducted in the main avocado growing areas in Sardinia and Sicily (Italy) to isolate and characterize the causal agents. Specifically, a total of 430 symptomatic leaf, fruit, branch, stem and root samples were collected and examined. Isolations performed on both non-selective and selective growth media yielded 22 species (fungi and oomycetes) belonging to the genera Botryosphaeria, Colletotrichum, Diplodia, Dothiorella, Macrophomina, Neofusicoccum and Phytophthora, including 14 new host–pathogen records in Italy. Notably, Neofusicoccum australe, Phytophthora cinnamomi and Phytophthora palmivora emerged as the main pathogens involved in the emerging avocado diseases. The identified pathogens were often isolated simultaneously from the same plants, which exhibited a complex of symptoms. Pathogenicity bioassays have helped to clarify the differences in aggressiveness among the different species and their specificity towards the different plant organs. The results achieved suggest that avocado orchards’ productivity and profitability is threatened by a plethora of unrelated pathogens whose control represents a major challenge for the success of this crop in Italy.