Alessandro Vitale

The main pathogens affecting the carob (Ceratonia siliqua) tree in the Mediterranean basin are described in this overview. The most widespread diseases periodically occurring in carob orchards are powdery mildew (Pseudoidium ceratoniae) and cercospora leaf spot (Pseudocercospora ceratoniae). The causal agents of “black leaf spots” (e.g., Pestalotiopsis, Phyllosticta and Septoria spp.) are responsible for symptoms similar to those previously mentioned for foliar diseases, but are reported in carob orchards at a negligible frequency. Likewise, canker and branch diebacks caused by fungal species belonging to Botryosphaeriaceae are almost never recorded. Among the rots of wood tissues that may compromise old carob specimens, “brown cubical rot” caused by Laetiporus sulphureus is the most widespread and recurrent issue; this pathogen is also well-known for producing edible fruit bodies that are appreciated for pharmaceutical and industrial purposes. On the other hand, “white rots” caused by Fomes and Ganoderma species are less common and reported for the first time in this review. Gall-like protuberances on twigs of uncertain aetiology or tumors on branches associated with Rhizobium radiobacter are described, although these symptoms are seldom detected, as they are also observed for necrotic leaf spots caused by Pseudomonas syringae pv. ciccaronei. A worldwide list of pathogens not yet recorded but at high risk of potential introduction in Italian carob-producing areas is also provided. Finally, concerns related to new phytopathogenic fungi vectored by the invasive Xylosandrus compactus ambrosia beetle are addressed. All the described pathogens could become limiting factors for carob production in the near future, because they could be favored by high-density orchards, the increasing global network of trade exchanges, and the high frequency at which extreme events related to climate change occur globally. Thus, symptoms and signs, causal agents, epidemiology, and, whenever applicable, recommendations for disease prevention and management are provided in this review.

Mal secco, caused by Plenodomus tracheiphilus, is an economically important fungal vascular disease in citrus-growing countries of the Mediterranean basin. Preventing fungal infections usually requires a high number of copper treatments but European legislation imposes the minimization of their accumulation in soil. In our study, biological control agents (BCAs) and a plant resistance inducer (PRI), tested in four different experiments on citrus seedlings under controlled conditions, have resulted in promising strategies to control mal secco disease. Foliar (Experiment I) and soil (Experiment II) applications of two formulations of Bacillus amyloliquefaciens strain D747 (Amylo-X® LC and Amylo-X® WG) provided similar performances in reducing the disease amount (incidence and symptoms severity) over time compared to the untreated control, whereas copper hydroxide (Kocide Opti®) used as standard was the most effective treatment over time. In the third experiment, Pythium oligandrum strain M1 (Polyversum®) and Trichoderma asperellum strain ICC012 + Trichoderma gamsii strain ICC080 (Remedier®) were able to reduce disease incidence and symptoms severity compared to the untreated control. Remedier® provided the best performances in reducing the disease amount, whereas the Polyversum® application was the least effective treatment over time. The effectiveness of the Trichoderma spp. formulation in reducing P. tracheiphilus infections did not significantly differ from the standard copper compound (Kocide Opti®). Comprehensively, in the last experiment (IV), acibenzolar-S-methyl (ASM) alone and in mixture with metalaxyl-M proved as effective as B. amyloliquefaciens strain FZB24, with no dose–response relationships observed. These findings provide important insight for the integrated management of mal secco disease.