Researchers Identify Compounds to Stem the Spread of Verticillium Wilt

A new study pub­lished in Frontiers in Plant Science by researchers from the University of Córdoba’s agron­omy depart­ment has iden­ti­fied a poten­tial strat­egy to stem the spread of Verticillium wilt.

Considered the most dis­rup­tive olive tree dis­ease due to its high lev­els of mor­tal­ity and the reduc­tion of fruit pro­duc­tion that takes place dur­ing the infec­tion, Verticillium wilt can sur­vive for up to 14 years in the soil.

As a result, find­ing a mit­i­ga­tion strat­egy has been a top pri­or­ity for researchers in olive oil-soaked Andalusia.

After more than a decade of inves­ti­gat­ing more than 20 dif­fer­ent com­pounds, researchers iden­ti­fied two ben­e­fi­cial microor­gan­isms – Aureobasidium pul­lu­lans and Bacillus amy­loliq­ue­fa­ciens – and a cop­per phos­phite fer­til­izer that may help con­trol the dis­ease.

Initially, the researchers tested the two microor­gan­isms and one com­pound in vitro but found they had no direct impact on the dis­ease.

However, when applied to the trees as a pre­ven­ta­tive mea­sure, the researchers dis­cov­ered that they improved the trees’ nat­ural defenses against the dis­ease before they became infected.

“We selected these three com­pounds because, applied via irri­ga­tion, in olive seedlings inoc­u­lated with V. dahliae [the fun­gus that spreads the dis­ease], they reduced the devel­op­ment of the dis­ease by up to 70 per­cent,” said Ana López-Moral, a researcher at the uni­ver­sity.

The researchers later dis­cov­ered that the microor­gan­isms and com­pounds could also effec­tively be applied through the leaves of the trees, mean­ing the treat­ment could also be applied in non-irri­gated groves too.

López-Moral added that each microor­gan­ism and com­pound pro­motes the resis­tance of the olive trees through dif­fer­ent mech­a­nisms, which par­tially explains the robust effec­tive­ness of the treat­ment in the study.

“The most strik­ing thing was that the induc­tion of resis­tance caused by the two microor­gan­isms used is reg­u­lated by dif­fer­ent meta­bolic path­ways,” she said. ​“While B. amy­loliq­ue­fa­ciens trig­gers the acti­va­tion of defenses through the sal­i­cylic acid path­way, when we apply A. pul­lu­lans, we detect that the path­way involved cor­re­sponds to that reg­u­lated by jas­monic acid.”

Along with pro­vid­ing resis­tance to Verticillium wilt, the researchers believe the com­pounds may also be effec­tive against other pathogens but stressed fur­ther research would be required to test this hypoth­e­sis.

For now, they are focus­ing on the next stage of this exper­i­ment, which involves field tests in olive groves grow­ing in var­i­ous cli­mates and soil types to deter­mine how effec­tive the treat­ment would be in prac­tice.

• Frontiers in Plant Science
• University of Córdoba