Olive knot damages in ten olive cultivars after late-winter frost in central Italy

Olive knot is among the most relevant diseases affecting olive cultivation. Pseudomonas savastanoi pv. savastanoi (Pss) is recognized as the causative agent of this disease. Its penetration in the plant occurs through wounds in all the aerial plant tissues. Frost, or hailstorm damages to the bark of shoots, branches and trunk might expose plants to higher risks of infection. In the coldest regions where freezing events may occur regularly, an employment of tolerant varieties to cold, or to Pss infection represents a valuable approach for limiting tree damages. However, the relationship between the tolerance to different frost types and the susceptibility to Pss disease in different organs (trunk, branches of different age) might be not univocal and rather change among olive tree varieties. In the Marche region of central Italy, the damages occurring during late winter frosts (end of February) and caused by olive knot disease were investigated. Our work considered 10 locally, nationally and internationally known cultivars that were studied under field conditions in 6 different groves in Marche region. In all the groves, olive knot incidence and severity were positively correlated with frost damaged organs. All the varieties were damaged by the late winter frost and showed olive knot disease symptoms after 6 months. 'Piantone di Mogliano', 'FS-17' and 'Frantoio' were the most affected cultivars. 'Carboncella', 'Maurino' and 'Arbequina' showed an intermediate susceptibility, whereas 'Ascolana Tenera' 'Leccino', 'Piantone di Falerone', 'Rosciola Colli Esini' resulted tolerant to this peculiar late frost and olive knot infection. The > 3-year-old branches were generally more damaged in comparison to younger branches.