Production

Hot Weather Reduced Olive Oil Quality and Yield in Small Study

Science may provide the answer to the consequences of global warming on olive trees to find cultivars with built-in tolerance to temperature extremes.
Jun. 23, 2020
Costas Vasilopoulos

Recent News

Researchers in Israel stud­ied the effects of high envi­ron­men­tal tem­per­a­tures on olive trees, deter­min­ing that intense heat reduced the quan­tity and qual­ity of olive oil and ulti­mately led to a reduced yield. Fur­ther research could develop olive vari­eties resilient to high tem­per­a­tures that would secure farm­ers’ crops against unsea­son­able warm weather and cli­mate change.

Olive trees are known for their resilience to extreme weather vari­a­tions. Global warm­ing, how­ever, has posed poten­tially great risks in many olive oil pro­duc­ing ter­ri­to­ries around the world where alter­nat­ing waves of extremes extend beyond their nor­mal weather pat­terns.

See more: Unusual Spring Heat Brings Early Prob­lems for Greek Farms

Higher-than-nor­mal heat brings early blos­som­ing. Colder days can freeze the blos­soms and pre­vent flow­er­ing and fruit devel­op­ment. Pro­duc­tiv­ity is dimin­ished and the olive oil yield is reduced.

To test how the olive trees behave in hot weather, the researchers placed five-year-old pot­ted trees of five dif­fer­ent olive vari­eties in two loca­tions: one with hot sum­mers with tem­per­a­tures often exceed­ing 40°C (104°F) and another with rel­a­tively mild sum­mers with tem­per­a­tures around 30°C (86°F).

The loca­tions were specif­i­cally selected so the trees expe­ri­enced tem­per­a­tures beyond the fluc­tu­a­tions nat­u­rally occur­ring in their usual olive oil pro­duc­ing ter­ri­to­ries.

Advertisement
See more: Unusual Weather Could Be Prob­lem­atic for Cal­i­for­nia Olive Crop

The cul­ti­vars used were the Barnea, Coratina, Suri, Picholine and Koroneiki.

The exper­i­ment spanned two har­vest­ing sea­sons and the trees were irri­gated. Each month olive dru­pes were sam­pled from the trees to undergo his­to­log­i­cal and phys­i­o­log­i­cal analy­ses and an oil accu­mu­la­tion eval­u­a­tion.

At the end of each sea­son, a cer­tain num­ber of dru­pes from all five vari­eties were har­vested and processed using a lab­o­ra­tory-scale cen­trifu­gal sys­tem.

The results showed that higher-than-usual tem­per­a­tures affected the olive fruit growth and weight, the oil accu­mu­la­tion in the fruits and the oil com­po­si­tion. The effects were found to be geno­type-depen­dent with each cul­ti­var exhibit­ing dif­fer­ent responses to peri­ods of intense heat.

In order to under­stand the mech­a­nism of the sen­si­tiv­ity and the resis­tance of olive cul­ti­vars to high tem­per­a­tures, we ana­lyzed the tran­scrip­tome [the RNA tran­scripts], ” researcher Giora Ben-Ari told Olive Oil Times.

We decoded the gene expres­sion pat­tern of all genes involved in the olive oil biosyn­the­sis. It seems like the main mech­a­nism of high tem­per­a­ture envi­ron­ment resis­tant is the abil­ity to delay fruit devel­op­ment and oil accu­mu­la­tion.”

In high tem­per­a­tures, the trees of the Barnea and the Koroneiki cul­ti­vars delayed the devel­op­ment of the olive fruits until milder tem­per­a­tures pre­vailed, while the olive fruit weight was reduced in all cul­ti­vars except the Barnea.

In terms of olive oil quan­tity, among the cul­ti­vars tested the Barnea exhib­ited sta­bil­ity against high envi­ron­men­tal tem­per­a­tures with fruit weight and con­tent of olive oil almost iden­ti­cal in olive fruits sam­pled from both loca­tions. The Koroneiki and the Suri cul­ti­vars were affected by warmer tem­per­a­tures with fruit weight and olive oil accu­mu­la­tion dimin­ish­ing in trees at the high tem­per­a­ture site com­pared to the trees at the mod­er­ate tem­per­a­ture site.

On the other hand, the qual­ity of the olive oil dete­ri­o­rated in all five cul­ti­vars in the high-tem­per­a­ture group. Oleic acid and polyphe­nol con­tent in the dru­pes sam­pled from the high-tem­per­a­ture site mea­sured lower than those sam­pled from the mod­er­ate-tem­per­a­ture site.

In con­clu­sion, the Koroneiki cul­ti­var appeared the most sus­cep­ti­ble to hot envi­ron­ments in all ana­lyzed para­me­ters among the cul­ti­vars tested. The Coratina and the Picholine were also affected but man­aged to retain the amount of oil in the olive dru­pes when exposed to warmer tem­per­a­tures, while the olive oil pro­duced from the Souri cul­ti­var retained to some extent its organolep­tic char­ac­ter­is­tics. The Barnea cul­ti­var exhib­ited some loss in the olive oil qual­ity, but retained the con­cen­tra­tion of oil and the weight of the olive fruits under heat.

Ben-Ari explained that apart from spec­i­fy­ing which cul­ti­vars are bet­ter suited to deal with intense heat, another objec­tive of their research is to cre­ate a breed­ing pro­gram’ to develop new vari­eties that exhibit increased tol­er­ance to higher tem­per­a­tures.

Future research will look at the gene expres­sion in order to under­stand the dif­fer­ences between sen­si­tive and resis­tant cul­ti­vars,” he said. This will help in breed­ing pro­grams to develop resis­tant cul­ti­vars. In addi­tion, last year we planted 100 cul­ti­vars in both loca­tions, and in the next sev­eral years we will screen these cul­ti­vars in order to iden­tify the resis­tant ones.”

Their results should be treated cau­tiously due to the rel­a­tively short time period and lim­ited sam­pling, the researchers noted. Nev­er­the­less, it could pave the way for more research on the sub­ject to yield use­ful data for grow­ers fac­ing increas­ing cli­matic extremes.



Advertisement

Related News