Ancient Olive Groves on Capri Are Reservoirs of Biodiversity

A study of the ancient olive trees on Capri has led to the dis­cov­ery of pre­vi­ously unknown olive vari­eties and other inter­est­ing insights into the age and ori­gin of the mon­u­men­tal trees grow­ing on the Italian island.

The research, pub­lished in Scientia Horticulturae by the Institute of Biosciences and Bioresources of the National Research Council (IBBR-CNR) of Perugia, fol­lowed more than a decade of restora­tion work done by L’Oro di Capri in the aban­doned olive groves on the west­ern part of the island.

“Our inves­ti­ga­tion focused pri­mar­ily on the ancient trees, accord­ing to the indi­ca­tions received by the asso­ci­a­tion’s tech­ni­cal com­mit­tee,” Soraya Mousavi, the research group’s leader, told Olive Oil Times. ​“We gath­ered 67 sam­ples from 27 mon­u­men­tal olive trees.”

The researchers col­lected sam­ples from the canopy and root­stock. ​“We usu­ally ana­lyze these two parts of the ancient trees sep­a­rately to detect whether there are graft­ing sce­nar­ios,” Mousavi said.

However, only canopy sam­ples were taken in 13 trees where a small trunk sprouted from the orig­i­nal stump or the trees grew like shrubs.

The mol­e­c­u­lar iden­ti­fi­ca­tion revealed that most sam­ples are genet­i­cally iden­ti­cal to the vari­ety Dritta di Moscufo, native to the cen­tral Italian region of Abruzzo.

Grafts were found in two olive trees, the canopies of which belong to the vari­ety, while most of the trees turned out to be clon­ally prop­a­gated.

The geno­types of a smaller group of sam­ples were iden­ti­cal to the Throumbolia vari­ety, mostly grown on the Greek island of Crete.

Furthermore, the genetic pro­files of Itrana, Frantoio and Leccino were found in a few other trees.

“An inter­est­ing find­ing is the detec­tion of 21 ancient geno­types which turned out to be unique after hav­ing been com­pared with 475 olive cul­ti­vars world­wide,” Mousavi said. ​“All this results in con­sid­er­able genetic diver­sity on the island.”

The plant mate­r­ial was geno­typed using sin­gle-sequence repeat mark­ers, widely applied for cul­ti­var char­ac­ter­i­za­tion in most olive germplasm col­lec­tions.

Now, the detected geno­types will enrich the IBBR-CNR col­lec­tion, which includes a data­base with more than 5,000 genetic pro­files and an olive DNA repos­i­tory with more than 10,000 sam­ples.

The data­base and repos­i­tory rep­re­sent fun­da­men­tal ref­er­ence points for germplasm banks at a national and inter­na­tional level.

“Having found trees of the Throumbolia vari­ety, we delved into the his­tory of the olive cul­ti­va­tion on the island to under­stand how and when these plants arrived,” co-author Roberto Mariotti said. ​“Documents pro­vided by our col­leagues who study the his­tory and arche­ol­ogy of the island tes­tify that olive cul­ti­va­tion was already prac­ticed 500 years ago.”

“The pres­ence of Greek peo­ple is attested in ancient times on the island,” he added. ​“We can hypoth­e­size that they intro­duced and cul­ti­vated vari­eties which seemed inter­est­ing at the time for trade or other pur­poses, espe­cially con­sid­er­ing that Throumbolia is a vari­ety with large fruits.”

Meanwhile, trees belong­ing to the Dritta vari­ety were likely brought to the island by fri­ars from the Moscufo monastery in the province of Pescara, Abruzzo.

Furthermore, birds may have played a part in spread­ing the other olive geno­types on the island.

“The olive trees have been both prop­a­gated by those who moved to the island bring­ing the trees with them from other places and born from seeds which have been dis­persed by birds, espe­cially migra­tors,” said co-author Saverio Pandolfi.

“Often due to these fac­tors, it is easy to find a rich genetic diver­sity within the olive trees wide­spread on islands,” he added. ​“Birds take the seeds from another place, keep them in their stom­achs or crops [part of the ali­men­tary tract used for stor­age of food before diges­tion] and even­tu­ally drop them.”

“Their diges­tive sys­tem cre­ates ideal con­di­tions for the devel­op­ment of the seeds, which then are nat­u­rally fer­til­ized and, once on the ground, ger­mi­nate very quickly,” Pandolfi con­tin­ued. ​“Whatever the ori­gin, from humans or birds, the genetic unique­ness of these plants makes them use­ful for the upcom­ing stud­ies.”

Radiocarbon dat­ing esti­mates that 12 mon­u­men­tal trees on the island are between 100 and 900 years old.

This is evi­dence that olive tree cul­ti­va­tion and domes­ti­ca­tion went on for a long time before the olive groves were aban­doned in the past cen­tury and even­tu­ally recov­ered by L’Oro di Capri.

“Identifying pre­vi­ously unknown ancient geno­types, which trans­late into new olive vari­eties at our dis­posal, has great util­ity when it comes to find­ing solu­tions for today’s global agri­cul­tural chal­lenges,” Mariotti said.

“The char­ac­ter­is­tics that have made the trees resis­tant for hun­dreds of years in this spe­cific envi­ron­ment can be exploited to address today’s issues, pay­ing par­tic­u­lar atten­tion to the urgent prob­lem of cli­mate change, which is greatly affect­ing the yield of the olive trees.”

Today, the unique geno­types found on the island may be used in upcom­ing breed­ing projects. In agro­nomic terms, the olive trees could be prop­a­gated and tested for envi­ron­men­tal and bio­log­i­cal stresses.

“These trees indeed rep­re­sent a use­ful genetic reser­voir that can be used to address new and emerg­ing dis­eases,” Pandolfi said. ​“Hence, they have a great value in terms of con­ser­va­tion of genetic mate­r­ial.”

In the study’s con­clu­sions, the researchers empha­sized how humans have con­tributed sig­nif­i­cantly to the dras­tic decrease in olive diver­sity at all lev­els, from sub­species to cul­ti­vars.

They thus believe it is now ​“manda­tory” to retrieve the rem­nants of ancient geno­types, start­ing with the study of mon­u­men­tal olive trees and their root­stocks, and to pre­serve the bio­di­ver­sity included in the ancient olive groves world­wide.

“We do not know much about the agro­nom­i­cal behav­ior of these olive trees, and now the aim is to under­stand this aspect,” Pandolfi said. ​“It is impor­tant to keep a data­base with all the infor­ma­tion col­lected, includ­ing their loca­tion and pho­tos. This will also help cre­ate an oleo­tourism itin­er­ary along which vis­i­tors can find sci­en­tif­i­cally val­i­dated infor­ma­tion.”