Researchers Identify Three Olive Varieties Resistant to Pervasive Fungus

Researchers in Spain have dis­cov­ered three olive vari­eties with genetic resis­tance to Verticillium dahlia, a soil-borne fun­gal pathogen deadly for olive trees.

The vari­eties were iden­ti­fied by researchers at the University of Jaén, the University of Córdoba and the Institute of Agricultural and Fisheries Research and Training (Ifapa) from genetic mate­r­ial obtained from the World Olive Germplasm Bank in Córdoba.

Verticillium dahlia pen­e­trates the roots of the olive tree. It causes the dis­ease Verticillium wilt, for which there is no effec­tive treat­ment, mak­ing resis­tant vari­eties a vital tool for olive grow­ers in regions highly sus­cep­ti­ble to the fun­gus.

Verticillium wilt causes the dete­ri­o­ra­tion of olive trees’ vas­cu­lar sys­tem with severe con­se­quences such as fruit and leaf drops. Over time, the fun­gus kills the infected trees.

Andalusia is the world’s largest olive oil-pro­duc­ing region, respon­si­ble for over half of Spanish olive oil pro­duc­tion. The region’s most prof­itable and com­monly grown olive vari­eties – Picual, Arbequina, Hojiblanca and Cornicabra – have all proven sus­cep­ti­ble to infec­tion from the fun­gus.

According to the autonomous community’s phy­tosan­i­tary infor­ma­tion and alert net­work, about 2.9 per­cent of olive trees in Córdoba and 88.9 per­cent of trees in Huelva, Andalusia’s sec­ond and sev­enth-largest olive oil-pro­duc­ing provinces, respec­tively, were infected by the dis­ease in 2022.

As a result, the researchers set about iden­ti­fy­ing olive vari­eties with nat­ural resis­tance to the fun­gal pathogen, eval­u­at­ing 31 dif­fer­ent vari­eties from the germplasm bank, three vari­eties known to be resis­tant to the deadly olive tree bac­terium Xylella fas­tidiosa and six vari­eties from Ifapa’s breed­ing cen­ter.

Previously, the researchers iden­ti­fied sev­eral genes that pro­tect trees against the fun­gus.

The cur­rent research aimed to iden­tify vari­eties that could main­tain the qual­ity and pro­duc­tion lev­els of the most pro­lific Spanish vari­eties, espe­cially those planted in high-den­sity and super-high-den­sity while pos­sess­ing nat­ural resis­tance to Verticillium dahlia.

After 12 months of cul­ti­va­tion, each of the 40 vari­eties was inoc­u­lated with the fun­gus, and their evo­lu­tion was mon­i­tored. Researchers planted 16 indi­vid­u­als of each vari­ety in four blocks. Three were infected with the fun­gus, and the last one, used as a con­trol, was not.

The three vari­eties that stood out in meet­ing all of the researchers’ cri­te­ria were cross­breeds of Frantoio and Koroneiki olives, both of which are resis­tant to the fun­gus, with Arbosana, a Spanish vari­ety fre­quently planted in high-den­sity and super-high-den­sity groves. The result­ing vari­eties were named ​‘FrxAr_5′, ​‘FrxAr_6′ and ​‘KorOp_48.’

The three vari­eties were cre­ated fol­low­ing stan­dard olive cross-breed­ing prac­tices; the researchers col­lected pollen from one vari­ety and pol­li­nated the sec­ond vari­ety, pro­duc­ing seeds with inher­ited char­ac­ter­is­tics from both par­ent vari­eties.

“The selected geno­types have shown that they inherit tol­er­ance and resis­tance to V. dahliae, which shows that they are ideal can­di­dates to develop new crosses between them and achieve more resis­tant and pro­duc­tive crops,” said Alicia Serrano, the lead author of the study and a researcher at the University of Jaén.

Encouraged by the ini­tial results of their study, the researchers said the next step was to plant these three vari­eties at a com­mer­cial scale in actual olive farms to observe how they fared against the dis­ease and other nat­ural stres­sors in real grow­ing con­di­tions.

• Scientia Horticulturae
• Discover Foundation