Fusarium euwallaceae, symbiont of the paninvasive polyphagous shot hole borer, is pathogenic to cultivated but not wild olive trees in South Africa

Fusarium euwallaceae, vectored by the paninvasive polyphagous shot hole borer beetle (Euwallacea fornicatus), is an emerging threat to trees globally. Proven pathogenic to cultivated deciduous fruits in South Africa, it recently has been isolated from cultivated European (Olea europaea subsp. europaea) and native African (Olea europaea subsp. cuspidata) olive. This potentially threatens both commercial production and native species conservation. However, pathogenicity to these trees is unknown. Three isolates were used in pathogenicity trials of F. euwallaceae towards cultivated European and African olives. Fusarium euwallaceae caused significantly longer lesions than the controls in vascular tissues of inoculated European olive trees, whereas no difference was observed for African olive. We therefore report for the first time that F. euwallaceae is pathogenic to cultivated European olive but not to African olive. As this fungus occludes affected xylem tissues, and thus water flow, olive fruit and oil production might be hampered during droughts, which are predicted to increase in severity and frequency in the main region olives are planted in in South Africa.