Greening is a disease caused by bacteria transported by specific insects that infest citrus trees, making fruits inedible. It has spread from China to vast areas of the world. It should affect Italy, the sector would risk collapse.
One of the most devastating diseases that affect citrus fruits is now at the gates of Europe. It is caused by such a bacterium Candidatus Liberibacteridentified for the first time in China in the early twentieth century and present in the Americas since early 2000. The disease that this bacterium causes is known how “Greening”name that derives from its most characteristic symptom: lemons, oranges, mandarins, grapefruits and lime remain green and do not ripen correctly due to the interruption of the transport of nutrients.
To spread it are the insects vectors diaphorina citri (Asian Psillide of citrus fruits) and Trioza Erytreae (African Psillide of citrus fruits), who with the mug system reach the tissues under the cortex of the plant and feed on the sap. If the tree is already infected, the bacterium enters its body, colonizes the digestive tract and the salivary glands and multiplies inside the body of the insect. When the psillide goes to feed on a healthy tree, the bacterium passes into the sap of the plant, where it begins to spread by generating a new infection. The disease, which can be recognized by the stunted growth, from the inline of the leaves, from small fruits and the progressive decline of the tree, is often described as the “new xylella” for the numerous characteristics in common with this other scourge of plants. In fact, both bacteria are transmitted by insects vectors that are difficult to control, affect the complex of fabrics used for the transport of nutrients and do not respond to any known cure.
Francesco Di Serio, director of the IPSP-CNR (Sustainable Protection Institute of CNR plants), clarifies an important point: «In order for the disease to spread in the European continent, two elements are needed: it takes the bacterium but also its carrier insect. While the bacterium that causes the greening of citrus fruits did not arrive in Europe, the Trioza Erytreae is present in Spain and Portugal (as well as on the island of Madeira and in the Canaria archipelago) and Diaphorina Citri was found in Israel and Cyprus. In the event that these insects should spread even more in our continent, and the bacterium should also arrive, the problems would be very serious. “It should be noted that the species that could more easily adapt to the high summer temperatures of Southern Italy in which citrus growing is widespread, is the Diaphorina Citri” specifies Di Serio.
In short, in the not too remote future we risk a very bitter reality. “The possibility that this disease landed in Europe, with a co -presence of Diaphorina Citri and the candidatus Liberibacter bacterium, is not to be excluded and this would mean the collapse of the sector”. As has already happened in Florida, whose surrender of the citrus groves is today only a fifth of what was in 1998, just before Greening would make its appearance. “The disease could spread from us through the arrival of an infected plant” hypothesizes serious, “although European legislation is iron regarding this kind of import from other countries, a unwary individual could transport or buy on the internet an infected plant or infested with infected carriers without knowing it, managing to escape controls, and causing the beginning of the epidemic”.
According to the European Commission, Italy and Spain are the major continental citrus producers with a cultivated surface of about 350 thousand hectares each. About two thirds of our production is in Sicily, where 50 thousand hectares are grown exclusively to orange trees, down last year mainly due to drought. For 2026 an increase of 20 percent at national level is expected, but always below average. Then who knows, it also depends on how good we will be good at fighting the arrival of greening.
We should fail, since there are no effective treatments for this disease, we would have only available management strategies to reduce the impact. The diffusion of the bacterium in other countries is contrasted through the control of psillid vectors through chemical treatments and biological control with the use of small parasites of the genus Tamarixia. Already in the early sixties both the Tamarixia species radiated together with another Vespa, the Diaphorencyrtus Aligarhensis, another parasite of Diaphorina Citri, were successfully introduced on the tropical island of La Réunion, in the Indian Ocean, markedly reducing the impact of the disease. The elimination of infected trees from which carriers can acquire and spread the bacterium is also fundamental. In Florida, antibiotic treatments and therapies with bacteriophagi are also studying that slow down the disease.
But the real and only hope is that the research is faster than diffusion, so as to be able to select, in the time that remains, variety of resistant citrus fruits.
