Monumental Trees of Cyprus Represent Attempt to Create Elite Cultivar

A recent study of mon­u­men­tal olive trees in Cyprus has shed light on a some­times cal­cu­lated, but always com­pli­cated agri­cul­tural his­tory.

“Based on the data of the cur­rent study it is safe to for­mu­late the con­clu­sion that ole­i­cul­ture in Cyprus has a com­plex his­tory,” Nikolaos Nikoloudakis of Cyprus University of Technology wrote.

“It is pos­si­ble that hybridiza­tion between local and or for­eign mate­r­ial, fol­lowed by the selec­tion of elite geno­types has repeat­edly occurred in dif­fer­ent eras with the goal of ame­lio­rat­ing the exist­ing geno­types.”

Researchers from Cyprus University of Technology and Agricultural University of Athens found a diverse amount of genetic mate­r­ial among these iconic olive trees. Since these trees range from hun­dreds to thou­sands of years old, the researchers see the preser­va­tion of this gene pool as immensely impor­tant for the future of olive trees.

“These are trees that have with­stood exten­sive and severe biotic and abi­otic adver­si­ties; hence con­sti­tute a valu­able and unex­ploited genetic pool,” said Andreas Katsiotis also of Cyprus University of Technology.

The researchers used gov­ern­ment records and field stud­ies to iden­tify and sam­ple 52 trees across north­ern Cyprus. They took DNA sam­ples from the leaves of each of the trees and com­pared them with a bench­mark of 20 known Greek cul­ti­vars.

The researchers sus­pect that the orig­i­nal olive grow­ers were try­ing to cre­ate an elite cul­ti­var of olive trees using an agri­cul­tural tech­nique known as graft­ing, which involves com­bin­ing parts of two or more plants so they grow together as one.

Much to their sur­prise, they dis­cov­ered that two-thirds of the mon­u­men­tal olive trees that were sam­pled had been grafted.

This find­ing led researchers to spec­u­late that early olive grow­ers had grafted the orig­i­nal cen­ten­nial trees with oth­ers imported from Greece and Lebanon in order to selec­tively breed for desir­able traits. Eventually, the prac­tice ceased and these grafted trees started to repro­duce nat­u­rally.

“The rich­ness in genetic resources is prob­a­bly the out­come of the early domes­ti­ca­tion of olive trees in Cyprus that occurred in antiq­uity, while genetic vari­abil­ity accu­mu­lated through time,” Nikoloudakis wrote. ​“Hence, these entries [sam­ples] rep­re­sent an unex­ploited gene pool.”

Grafting was pre­vi­ously thought to be a tech­nique that had been used for hun­dreds of years. However, these find­ings are proof that it may have been used thou­sands of years ago as an orga­nized and exten­sive pro­ce­dure.

As a result of the graft­ing all the genetic diver­sity within the pop­u­la­tion could be traced back to only a por­tion of the cen­ten­nial trees.

“This was a rev­e­la­tion since selec­tion of elite cul­ti­vars since antiq­uity is evi­dent. As a result, the mod­ern Cypriot vari­eties resulted from an assort­ment of a few ancient elite clones,” Katsiotis said. ​“Furthermore, this means that there is still a lot of genetic diver­sity ​‘out there’ to be uti­lized in order to pro­duce adapted vari­eties with high supe­rior attrib­utes.”

The genetic diver­sity that is ​“out there” could be used to breed trees that yield more olives as well as are more resis­tant to dis­ease and adverse cli­matic con­di­tions, if the cor­rect genes are found within the pop­u­la­tion.

“Elite cul­ti­vars are bet­ter than oth­ers in major agro­nomic traits includ­ing resis­tance of biotic and abi­otic stresses and high yield poten­tial,” said Young-Chan Cho of the National Institute of Crop Science in Japan.

Among these traits, Cho sug­gested that breed­ing elite cul­ti­vars may also be use­ful for resist­ing insects. The olive fruit fly is the main car­rier of the olive tree-killing dis­ease, Xylella fas­tidiosa. Cyprus is among the eight European Union nations most con­cerned about the dis­ease, but has not suf­fered major out­breaks such as those seen in Spain, Italy and France.

Katsiotis said that a large pool of genetic diver­sity is the pre­req­ui­site for breed­ing these elite cul­ti­vars. However, more research would need to take place in order to deter­mine whether those traits exist in the Cypriot gene pool.

“Surely these geno­types are well adapted in the dry east­ern Mediterranean cli­mate, but we can­not be cer­tain if they will exhibit sig­nif­i­cant resis­tance to exotic pathogens with­out fur­ther exper­i­men­ta­tion,” he said.

• Public Library of Science


• BioMed Central