A study published yesterday (29 March) by the European Food Safety Authority (EFSA) confirmed that the Xylella fastidiosa bacterium is responsible for the large-scale destruction of Italy’s olive crop.
After two years of scientific investigation, EFSA, which is based in the northern Italian city of Parma, confirmed the long-held belief that the pathogen is the cause of the problem, which has primarily affected the southern region of Puglia.
“These findings confirm that the CoDiRO strain of X. fastidiosa causes olive dieback. This is an important step forward because we can only accurately assess the risk of an epidemic spreading from Apulia if we know more about the Apulian strain,” said Giuseppe Stancanelli, head of EFSA’s Animal and Plant Health Unit.
During the course of the study, scientists analysed Mediterranean crops such as olive, grape, citrus, almond, peach, cherry and plum, as well as forest species such as oak.
Investigators from the Italian National Research Council exposed the species to the bacterium through artificial means in the laboratory and via infective insect vectors in the field.
The olive plants tested displayed similar symptoms to those observed in the field, such as desiccation, but not all the varieties responded in the same way, with different types succumbing to the infection at varying rates, depending on the concentration of the pathogen.
Stancanelli urged researchers to continue their work, so that farmers could eventually be provided with information that would allow them to grow olive varieties that are more resistant or even immune to the bacteria.
The investigation also revealed that an insect common to the area, the meadow froghopper, can transmit Xylella to olives and other plants, with infection detected as early as six months after initial exposure to the bugs. Citrus plants, grape vines and holm oak remained immune to the pathogen via this means of exposure.
EFSA announced that all of the plants that have been innoculated will be kept under observation for one more season and field experiments will be continued for up to a decade.
The pathogen was first detected in Puglia in 2013, where it has destroyed thousands of trees and led the local authorities to destroy hundreds more as a precautionary measure. Olive farmers have protested at the destruction of their livelihood and many have launched legal challenges against the forced removal of trees that take up to two decades to start producing fruit.
Last year, the infection was detected on Corsica and France’s southern coast, which has caused European authorities to up their efforts in intensifying checks and strengthening containment measures.
However, the olive groves of Andalucía have been declared Xylella-free, after over 600 checks and tests were carried out.
Xylella fastidiosa mainly affects olive plants, with infected trees displaying scorched leaves, dried branches and rapid deterioration, which in the most severe cases causes the death of the tree.