Olives with Higher Phenol Content More Resistant to Anthracnose

Researchers found that olive varieties that maintained high concentrations of certain phenolic compounds during ripening were less likely to develop anthracnose.
(Photo: Valmir Duarte)
By Daniel Dawson
May. 23, 2024 11:20 UTC

Scientists from the University of Córdoba’s olive genet­ics research group have found that changes in the phe­no­lic pro­files dur­ing the olive ripen­ing process play a fun­da­men­tal role in the resis­tance to anthrac­nose.

The eco­nom­i­cally dam­ag­ing olive tree dis­ease is caused by the Colletotrichum fun­gus. The fun­gus causes severe rot in olives, lead­ing to sig­nif­i­cant crop losses.

Olive oil from olives con­t­a­m­i­nated by fun­gus has higher acid­ity and organolep­tic defects. It usu­ally falls into the lam­pante cat­e­gory and is unsuit­able for human con­sump­tion.

See Also:Researchers Identify Three Olive Varieties Resistant to Pervasive Fungus

We ana­lyzed six vari­eties for two years, car­ry­ing out analy­ses of phe­no­lic com­pounds and resis­tance tests to the pathogen,” said Hristofor Miho, a PhD stu­dent at the University of Córdoba and first author of the study.

The results allowed us to observe that resis­tance was greater in vari­eties with high phe­no­lic con­cen­tra­tions and spe­cific phe­nols present in them,” he added.

The researchers selected Empeltre and Frantoio cul­ti­vars, known for their resis­tance to the fun­gus; Hojiblanca and Picudo, known for their lack of resis­tance; and Barnea and Picual, con­sid­ered mod­er­ately resis­tant.

Olives were har­vested from the World Olive Germplasm Bank of Córdoba before they began to ripen and at three ripen­ing stages: green, turn­ing and ripe.

Samples were taken to deter­mine the olives’ phe­no­lic pro­files, and they were then inoc­u­lated using spores of the most com­mon Colletotrichum strain found in Spain and Italy.

While all green olives are immune to the fun­gus, they accu­mu­late inac­tive Colletotrichum infec­tions in the form of appres­so­ria, an organ-like struc­ture that pen­e­trates the fruit.

This infec­tion remains latent dur­ing fruit devel­op­ment until ripen­ing, result­ing in pathogen reac­ti­va­tion and dis­ease devel­op­ment,” the researchers wrote. Subsequently, olive fruit sus­cep­ti­bil­ity to the pathogen increases dur­ing ripen­ing, while in par­al­lel, there is a decrease in total phe­no­lic com­pounds.”

The researchers also iso­lated seven stan­dard phe­no­lic com­pounds to test their anti­fun­gal activ­ity: hydrox­y­ty­rosol, tyrosol, oleu­ropein, oleu­ropein agly­cone, olea­cein, oleo­can­thal and hydrox­y­ty­rosol 4‑O-glu­co­side.

Oleocanthal exhib­ited the high­est inhibitory activ­ity, fol­lowed by olea­cein, oleu­ropein agly­cone, hydrox­y­ty­rosol and tyrosol,” the researchers wrote.

See Also:Genotype Plays Significant Role in Fatty Acid Content of Virgin Olive Oil

Oleuropein, ligstro­side (the pre­cur­sor of oleo­can­thal) and their deriv­a­tives, includ­ing olea­cein, were the most crit­i­cal com­pounds inhibit­ing spore ger­mi­na­tion.

The com­pounds are pre­dom­i­nant in all green fruits regard­less of cul­ti­var and rep­re­sent more than 90 per­cent of total phe­nols dur­ing ripen­ing of the main resis­tant cul­ti­vars.

Meanwhile, sus­cep­ti­ble cul­ti­vars con­verted oleu­ropein, olea­cein and oleo­can­thal into hydrox­y­ty­rosol-4-O-glu­co­side as they ripened, which reduced anthrac­nose tol­er­ance.

Overall, resis­tant cul­ti­vars induced the syn­the­sis of alde­hy­dic and demethy­lated forms of phe­nols [oleu­ropein, oleo­can­thal and olea­cein], which highly inhib­ited fun­gal spore ger­mi­na­tion,” the researchers wrote. In con­trast, sus­cep­ti­ble cul­ti­vars pro­moted the syn­the­sis of hydrox­y­ty­rosol 4‑O-glu­co­side dur­ing ripen­ing, a com­pound with no anti­fun­gal effect.”

They fur­ther found that a total phe­no­lic con­cen­tra­tion of 50,000 mil­ligrams per kilo­gram in all sam­ples of devel­op­ing olives across cul­ti­vars com­pletely inhib­ited spore ger­mi­na­tion.

The researchers observed that cul­ti­vars sus­cep­ti­ble to the fun­gus expe­ri­enced a 73 per­cent decline in phe­no­lic com­pounds dur­ing ripen­ing, while resis­tant cul­ti­vars expe­ri­enced a 28 per­cent decline.

The sharp phe­no­lic reduc­tion of the sus­cep­ti­ble cul­ti­vars caused the com­plete reduc­tion of the anti­fun­gal activ­ity,” they wrote. Interestingly, the lesser phe­no­lic decrease of the resis­tant cul­ti­vars did not reduce the inhibitory effect of spore ger­mi­na­tion.”

Juan Moral, who over­saw the research, said the study would help pol­i­cy­mak­ers and farm­ers select new vari­eties to plant and inform researchers about what vari­eties to cross­breed for more resis­tant hybrids.

Knowing how the phe­no­lic cas­cades [changes in the phe­no­lic com­pounds] behave in the dif­fer­ent vari­eties will allow us to bet­ter select, based on sci­en­tific cri­te­ria, the par­ents that should be used so that the fol­low­ing gen­er­a­tions of olive trees are resis­tant to this dis­ease,” he con­cluded.


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