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Research Reveals How Deadly Pathogen Infects Olive Trees

Researchers from the University of Córdoba studied how fluid emitted by olive tree roots facilitates the germination of the fungus responsible for Verticillium wilt.
Verticillium
By Simon Roots
Feb. 6, 2023 15:10 UTC

Using a new method of in vitro analy­sis, researchers from the University of Córdoba’s agron­omy depart­ment have proven how fluid emit­ted from olive tree roots allows the ger­mi­na­tion of the fun­gus that causes Verticillium wilt.

The researchers hope the find­ings, pub­lished in Plant and Soil, will pave the way to more effec­tive con­trol mea­sures for the soil-borne fun­gal dis­ease that affects a wide range of plants, includ­ing olive trees.

The best way to estab­lish con­trol mea­sures in a ratio­nal way against crop pathogens is to know in depth the mech­a­nisms involved,” said Antonio Trapero-Casas, a pro­fes­sor of plant pro­duc­tion at the uni­ver­sity. This study is an attempt to get to know these mech­a­nisms involved,” he added.

See Also:Understanding Relationship Between Fungus and Climate May Curb Costly Olive Tree Pathogen

Verticillium wilt is cur­rently one of the biggest threats to olive groves world­wide because there is no known method of con­trol­ling it effec­tively.

Though there are resis­tant olive cul­ti­vars, they are less pro­duc­tive and still vul­ner­a­ble. Picual, the most com­mon com­mer­cial cul­ti­var, is also the most sus­cep­ti­ble to the pathogen.

In 2021, the University of Córdoba’s agron­omy depart­ment said its four-year efforts at com­bat­ing Verticillium wilt by graft­ing Andalusian olive trees with resis­tant vari­eties, the most promis­ing strat­egy to date, had failed to pro­duce results in the field.

Once Verticillium dahliae, the fun­gus that causes the wilt, has infected a host, it becomes vul­ner­a­ble to sev­eral other types of fungi, bac­te­ria and pro­to­zoa.

Opportunistic microbes also come into play, such as nema­todes and amoe­bae, which, although not ini­tially involved in the infec­tion, feed on the sub­stances gen­er­ated by the olive tree’s nat­ural defense mech­a­nisms.

A major obsta­cle to con­trol­ling the pathogen is its abil­ity to sur­vive in the soil for up to 14 years until it encoun­ters the roots of its host plants, which, dur­ing growth, secrete sub­stances called exu­dates that influ­ence sur­round­ing microor­gan­isms.

To study the role of these exu­dates, the researchers extracted sam­ples from three olive cul­ti­vars: Frantoio, the most resis­tant; Arbequina, a cul­ti­var with medium resis­tance; and Picual, the most sus­cep­ti­ble.

They found that exu­dates from Frantoio did not sig­nif­i­cantly result in the ger­mi­na­tion of Verticillium microscle­ro­tia, while exu­dates from the sus­cep­ti­ble vari­eties did.

Verticillium microscle­ro­tia

Verticillium microscle­ro­tia are small, hard struc­tures pro­duced by the Verticillium wilt fun­gus that can sur­vive in soil for sev­eral years. They serve as the pri­mary source of infec­tion for new plant hosts and are the means by which the fun­gus per­sists in the soil from one sea­son to the next.

The researchers then ana­lyzed how the bio­log­i­cal con­trol agents applied to the dif­fer­ent olive vari­eties could alter the func­tion of the exu­dates.

This analy­sis showed that in Frantoio, exu­dates from treated plants nei­ther induced nor sig­nif­i­cantly reduced the ger­mi­na­tion of pathogen resis­tance struc­tures. In con­trast, exu­dates from treated Picual or Arbequina plants sig­nif­i­cantly reduced the via­bil­ity of these struc­tures.

Researchers said this result is sig­nif­i­cant because it sug­gests that bio­con­trol agents can mod­u­late the effect of exu­dates, thus decreas­ing the abil­ity of the pathogen to infect sus­cep­ti­ble cul­ti­vars.

The result builds upon researchers’ 2022 find­ing that apply­ing Aureobasidium pul­lu­lans and Bacillus amy­loliq­ue­fa­ciens, two microor­gan­isms, and a cop­per phos­phite fer­til­izer boosted the olive trees’ nat­ural defenses against the fun­gus.



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