Researchers Study How Lack of Chill Hours Impacts Olive Development, Oil Quality

The lack of chill hours has resulted in longer flowering periods, more oil accumulation and distinct oil chemistry in olives grown in the subtropical climate of Tenerife.

Guacimara Medina (left) in Tenerife (Photo: Lorenzo León)
Nov. 14, 2022
By Daniel Dawson
Guacimara Medina (left) in Tenerife (Photo: Lorenzo León)

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Rising annual aver­age tem­per­a­tures across much of the olive-grow­ing world have cre­ated uncer­tainty that olive trees will receive the nec­es­sary 200 to 600 chill hours between 2 ºC and 10 ºC required to enable ver­nal­iza­tion.

Researchers from the Andalusian Institute of Agricultural, Fisheries, Food and Organic Production Research and Training (IFAPA) and the Canary Islands are work­ing on an ongo­ing study to deter­mine which of the world’s most pop­u­lar olive vari­eties may be best pre­pared for ris­ing win­ter tem­per­a­tures in the most pro­duc­tive olive oil-pro­duc­ing region on Earth.

The the­o­ret­i­cal mod­els… fore­cast that when there is no win­ter chill, the olive will not flower. But when we went to the Canary Islands, we found that what actu­ally hap­pens when there is no win­ter chill is very dif­fer­ent.- Raúl de la Rosa, senior researcher IFAPA

We are very wor­ried about cli­mate change, and there were a lot of papers or mod­els fore­cast­ing what will hap­pen with cli­mate change in the future in the Mediterranean with olives,” Raúl de la Rosa, a senior researcher at IFAPA, told Olive Oil Times.

However, all the mod­els were based on the­o­ret­i­cal assump­tion, and no prac­ti­cal tri­als had been done about what hap­pens when you plant olive trees in a place where there is no win­ter,” he added.

See Also:Experiment with North African Olive Varieties Bears Fruit in Croatia

On the island of Tenerife, the largest and most pop­u­lous of the Canary Islands, com­mer­cial olive grow­ing began in 2005.

According to data from Aemet, the state-run mete­o­ro­log­i­cal agency, aver­age win­ter tem­per­a­tures on the arable parts of the island range from 12.5 ºC to 17.5 ºC, with aver­age daily lows between 10 ºC and 12.5 ºC. In Andalusia, aver­age win­ter tem­per­a­tures gen­er­ally sit within the 2 ºC to 10 ºC win­dow.

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Some cli­mate mod­els pre­dict that the cur­rent warm­ing trend will result in Andalusia’s win­ter tem­per­a­tures more closely match­ing those of the Canary Islands in the next 30 years.

Over the past six years, the IFAPA researchers and their local part­ners planted Picual, Hojiblanca, Cornicabra, Arbequina, Coratina, Korneiki and Martina – a cross of Picual (also known as Marteño) and Arbequina – near Córdoba and Málaga, in Andalusia, and on Tenerife.

Each of the three grove loca­tions has markedly dif­fer­ent cli­mates, with the groves near Málaga expe­ri­enc­ing slightly higher aver­age win­ter tem­per­a­tures than those in Córdoba.

This helped the researchers deter­mine that tem­per­a­ture was caus­ing the main dif­fer­ences between olive devel­op­ment in Tenerife and Córdoba instead of other fac­tors such as soil com­po­si­tion.

Since the study began, the researchers have observed sev­eral marked dif­fer­ences in how olives behave in Tenerife com­pared to Andalusia, with the most notice­able dif­fer­ences involv­ing the olive tree flow­er­ing period, oil accu­mu­la­tion and chem­i­cal com­po­si­tion.

The the­o­ret­i­cal mod­els that were pro­duced here in the penin­sula fore­cast that when there is no win­ter chill, the olive will not flower,” de la Rosa said. But when we went to the Canary Islands, we found that what actu­ally hap­pens when there is no win­ter chill is very dif­fer­ent.”

Instead, Guacimara Medina, an agri­cul­tural exten­sion tech­ni­cian and Ph.D. researcher involved in the study, told Olive Oil Times that olives planted in the Canary Islands have two flow­er­ing peri­ods from January to May.

When there’s no win­ter chill, the olive trees always flower, but for much longer than in Andalusia, and there are sev­eral flow­er­ing peri­ods from January to May,” she said. The flow­er­ing period is longer, and the olive trees flower for three months, some­times more.”

As a result of the extended flow­er­ing peri­ods and their non-endemic nature on Tenerife, Medina added that the trees were increas­ingly sus­cep­ti­ble to dam­age from pests, requir­ing more inten­sive phy­tosan­i­tary inter­ven­tion.

See Also:Climate Change Taking a Toll on Andalusian Olive Oil Production

Along with the flow­er­ing period, Medina said that oil accu­mu­la­tion was much higher in olives grown on the island.

Due to the mild tem­per­a­tures, the oil accu­mu­la­tion does­n’t stop,” she said. In Mediterranean con­di­tions, the oil accom­mo­da­tion fin­ishes when the tem­per­a­tures decrease.”

However, Tenerife’s sub­trop­i­cal cli­mate means that oil accu­mu­la­tion can reach up to 60 per­cent, com­pared to 20 per­cent in the most effi­cient vari­eties in Andalusia.

Early flow­er­ing and the con­tin­ued oil accu­mu­la­tion also mean many olives are ready to be har­vested by the end of July or early August in the Canary Islands, mak­ing it the first palace to pro­duce olive oil each crop year in the European Union.

As a result, Medina said that local pro­duc­ers on the island are seek­ing a pro­tected geo­graph­i­cal cer­ti­fi­ca­tion, such as a Protected Designation of Origin (PDO) or Protected Geographical Indication (PGI), to help pro­mote the island’s oils.

In terms of chem­i­cal com­po­si­tion, Medina said olives grown on Tenerife have a dis­tinct polyphe­nol pro­file com­pared to their coun­ter­parts in Andalusia.

The polyphe­nols are dif­fer­ent and higher than in Andalusia,” she said. Specifically, there are more toco­pherols, an organic chem­i­cal com­pound with vit­a­min E activ­ity, in Canarian oils than in Andalusian oils.

However, higher year-round tem­per­a­tures also sig­nif­i­cantly lower the mar­gin for error dur­ing the trans­for­ma­tion process to ensure that all the oil yielded meets the extra vir­gin olive oil stan­dards.

De la Rosa said other stud­ies have shown that when oil accu­mu­la­tion in Arbequina olives hap­pens at higher tem­per­a­tures, oleic acid con­cen­tra­tions decrease while linoleic acid con­cen­tra­tions rise.

So the sta­bil­ity of the oil is very low,” he said. This is a big prob­lem. In the future, if the oil accu­mu­la­tion occurs at a higher tem­per­a­ture, it will neg­a­tively affect the olive qual­ity.”

Our job is to look for cul­ti­vars with the genet­i­cally higher sta­bil­ity of the oil,” he added.

For exam­ple, de la Rosa said Martina – the cross between Picual and Arbequina – has shown promise. So maybe in a future cli­mate sce­nario, we will use mainly cul­ti­vars like those,” he said.

However, the research tri­als – the most recent of which started six months ago – must con­tinue before con­crete con­clu­sions can be reached.


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