Gotta Infect 'Em All: Evidence for an Expanded Host Range of Spilocaea oleagina in Wild Olive Taxa

Olive scab, caused by Spilocaea oleagina, is one of the most widespread foliar diseases of cultivated olive, yet its host range within wild Olea europaea taxa remains poorly documented. In this study, the susceptibility of a panel of wild olive taxa (oleaster, O. europaea subsp. maroccana, subsp. laperrinei, subsp. africana, and an africana×europaea hybrid) was evaluated under artificial inoculation and natural infection conditions, using the cultivars Picual and Frantoio as susceptible and resistant reference cultivars, respectively. Disease incidence and severity were assessed weekly for 10 weeks, and disease intensity was summarized as the relative area under the disease progress curve (rAUDPC) of the disease index. All taxa developed symptoms under both inoculation method and natural infection. Specifically, natural infection of tree canopy resulted in significantly higher disease levels than artificial inoculation and produced a more gradual disease progression, consistent with prolonged exposure to inoculum. Taxon-specific differences were detected across inoculation methods, with the hexaploidy subsp. marrocana being highly resistant to the pathogen. These results provide experimental evidence that susceptibility to S. oleagina extends across multiple wild Olea europaea taxa and an inter-subspecific hybrid, highlighting the epidemiological relevance of wild olives at cultivated-wild interfaces as sources of inoculum and their potential value as resistance sources for breeding programs.