The European Food Safety Authority (EFSA) said on 29 March that a new study has confirmed that Xylella fastidiosa is responsible for the olive quick decline syndrome, which is destroying olive trees in southern Italy.

An investigation has been taking place over the last few years in Apulia to distinguish which species are hosts of Xf CoDiRO (the specific name of the Xf strain observed in the region).

The study was conducted by scientists from the Italian National Research Council and funded by the EFSA, and involved exposing varieties of perennial crops to the bacterium through artificial inoculation and by exposure to infectious insect vectors.

A range of Mediterranean crops were tested including olive, grape, almond and citrus, as well as forest species such as holm oat and ornamentals such as myrtle-leaf milkwort.

According to the head of EFSA’s Animal and Plant Health Unit, Giuseppe Stancanelli, “These findings confirm that the CoDiRO strain of Xf 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 fill knowledge gaps on the host range and epidemiology of the Apulian strain.”

Both the inoculated olive plants and the field plants exposed to insect vectors showed severe symptoms including desiccation and dieback.

However, EFSA said that not all varieties of olive reacted in the same way. In Coratina, Leccino and Frantoio the bacterium had a lower concentration and took longer to colonise, compared to Cellina di Nardò – one of the most common cultivators in the infected area.

According to the results of the study, an insect that is widespread in Apulia, the spittlebug, is able to transmit the bacterium to olive, as well as other species.

Stancanelli also said that “The results from this project significantly reduce the uncertainties surrounding the risks connected to Xf strain CoDiRO for the EU territory and will help in the planning of future research.”

Subsequent tests will aim to identify tolerant or resistant varieties of olives, he added, which could be grown in the contaminated areas.