BIOVEXO going Apulia

Wrap-up from a Consortium Meeting and Field Trip to Locorotondo on Oct. 27-29th, 2021.

Apulia, a charming region in the heel of Italy, is famous for many things: historical ports and picturesque Trulli stone houses, subtropical feelings at its southern beaches, renowned food and wine and, of course, vast olive plantations producing its famous olive oil.

Trulli stone houses, landmark of the city of Alberobello in central Apulia; photo credit

Unfortunately, as we have witnessed ourselves during the BIOVEXO field visit to Apulia, not all olive plantations are doing well, quite the contrary. Apulia is the first European region infected by the bacterium Xylella fastidiosa. A particularly severe strain of Xylella, strain pauca, is attacking and killing olive trees at an unprecedented pace.

Large scale olive plantations infected by Xylella in Southern Apulia; photo credit Stephen Webb

Xylella is the reason why the BIOVEXO project has been conceived and funded within the Bio-based Industries Joint Undertaking, a subprogram of Horizon 2020. BIOVEXO aims at developing bio-control solutions to combat Xylella in a comprehensive integrated pest management approach. At present, only chemical solutions are available to control the insect vector, while no cure has been developed for the infected plants.

New plantation next to a dead olive grove; photo credit Luis Rodrigues

Whereas southern Apulia is heavily hit, northern Apulia is relatively unaffected, hindered through demarcation zones implemented by the local authorities. To prevent further Xylella spread, BIOVEXO develops solutions targeting the spittlebug mainly responsible for transmission of the bacterium as well as curative treatments for early infected trees.

After 18 months of lab development and greenhouse trials, BIOVEXO testing is ready to scale up. Four field trials are set up with 200 plants each, which will be monitored for at least two seasons. Products are tested in either preventive (i.e. newly planted olive trees) or curative (i.e. already infected trees) trials on susceptible cultivars Cellina di Nardò and Arbequina in orchards located in Avetrana, Latiano and Brindisi. Plants are thus exposed to infections occurring under ranging natural conditions.

BIOVEXO partners visiting the CNR/CRSFA experimental field in southern Apulia; photo credit Stephen Webb

In one of the preventive test fields close to the port of Brindisi, a grove of the susceptible olive cultivar Cellina di Nardó is treated with all products that BIOVEXO has in its arsenal for comparative testing. The complexity of the trials is further increased by testing different product delivery methods to the plant. Presently, foliage spraying and drip irrigation are tested; more costly but potentially more effective endotherapy is also considered. In each case, the severity of the tree infection is assessed by visual assessment of branches in the cardinal directions of the tree, and then via quantitative PCR tests in the lab to detect the presence of Xylella. Treatment and assessments are carried out with a six months cadence on all the plants under testing.

BIOVEXO experts Stéphane Compant (l) and Pasquale Saldarelli (r) inspecting the extend of infection; photo credit Stephen Webb

Curative treatment is applied to susceptible cultivar Cellina di Nardò in a test field close to the city of Latiano. Project partners CNR-IPSP and CRSFA treat there with BIOVEXO products two large plots with eight or twenty years old trees. Probably due to an overall very heavy concentration of the inoculum, no conclusive positive effects could have been recorded until now. While the evaluation of curative trials on 15 years old trees of cultivar Arbequina in Brindisi is suspended, a new assessment is planned for the season 2022.

BIOVEXO aims to develop a biologically based, integrated pest management strategy, targeting not only the Xyllela bacterium, but also its insect transmitter (vector), the spittlebug. Trials are conducted according to the insect life cycle and BIOVEXO products are applied to the juvenile and adult stages.  It has been found out that applying products early in the year and the resulting reduction of the population of juveniles have the largest effect throughout the vegetation period. Different efficacies among the products tested were also observed regarding mortality of the insects and persistence of the product throughout time.

Surveillance of the spittlebug population in the olive grove; photo credit Stephen Webb

In summary, the Xylella epidemic in Apulia is complex, both due to the severity of the disease in olive trees and due to the intensity and spread of the inoculum. Obviously, bio-solutions have the chance only in combination with appropriate grove management and conscious compliance with the regulations aiming at easing the pest situation. Yet, we are confident, in connection with tests also in other regions of Europe, different cultivars and/or different climate conditions, BIOVEXO will develop a comprehensive set of bio-control products and methodologies to contain Xylella and to live with it in an acceptable way.

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