Re-Evaluating the Etiology of Citrus "Dothiorella Gummosis" in Italy

Citrus is one of the most important crops in Italy, especially in the southern regions. Field surveys conducted in the main production areas of southern Italy, regulated by the EU geographical indications system, revealed the presence of symptomatic citrus trees (lemon, mandarin, sweet orange, bergamot, and grapefruit) showing severe trunk and branch canker and gummosis. This disease, formerly known as "Dothiorella gummosis," has been reinvestigated in light of the new advances of fungal taxonomy. A total of 120 fungal isolates were characterized, and representative ones were tested for their pathogenicity. Multilocus phylogenetic analyses revealed the presence of different species including Boeremia exigua, Diaporthe foeniculina, Didymella nigricans, Dothiorella viticola, Fusarium caatingaense, F. citricola, F. falsibabinda, F. juglandicola, F. salinense, F. sarcochroum, Lasiodiplodia mediterranea, Neocosmospora metavorans, Neofusicoccum parvum, and Neoscytalidium dimidiatum. Pathogenicity tests were conducted by inoculating mycelial plugs on healthy potted citrus plants. Symptoms were evaluated 30 days after the inoculation. Results showed that the following species were pathogenic: B. exigua, D. foeniculina, D. viticola, L. mediterranea, N. metavorans, N. parvum, and N. dimidiatum. Among the fungal species identified in this study, N. parvum proved to be the most widespread across all the surveyed areas, and B. exigua, N. metavorans, and N. parvum were the most aggressive. This study represents a new update on the diversified etiology of citrus trunk and branch canker and gummosis in Italy.