Cross-infection and asymptomatic colonization by Botryosphaeriaceae fungi on lignified stems of apple and olive, and dormant cuttings of grapevine

Botryosphaeriaceae pathogens have broad host ranges and can move between hosts, particularly those with overlapping geographic distributions. Cross-infection potential and virulence were assessed for 40 isolates of Botryosphaeria, Diplodia, and Neofusicoccum (11 species), originally isolated from apple, olive, or grapevine crops. Progression of asymptomatic colonization beyond visible necrotic lesions was also assessed, to determine minimum pruning distances required for effective pathogen removal. The assays were conducted using detached lignified stems of apple and olive, and dormant cuttings of grapevine. All the isolates cross-infected and colonized stems or cuttings of the three potential hosts, confirming host-independence of these pathogens. Most of the Neofusicoccum isolates consistently caused the largest lesions across the three inoculated hosts. Asymptomatic colonization was not detected at distances of 20 or 30 cm beyond visible lesions. However, at 10 cm, one isolate of N. parvum colonized the three hosts, and one isolate of D. seriata colonized olive host. These results highlight the challenges for managing these pathogens in fruit crops growing in close proximity, and emphasize the urgency of revising the minimum pruning distances required for successful pathogen removal.