1 Where does this disease come from?
Currently, this Huanglongbing disease (HLB) is the deadliest for citrus in the world, according to the Center for International Cooperation in Agricultural Research for Development (CIRAD), based in France, which coordinated this work published at the end of December.
Since the 2000s, it has decimated the harvests of major producers such as China or the United States, which are forced to use antibiotics and insecticides on a massive scale.
Until then, Europe had been spared this scourge. However, a team of researchers has discovered that a tiny insect observed in Spain and Portugal for five years, the African leaf flea Trioza erytreae, was able to transmit the bacterium that causes the severe form of HLB.
2 African bacteria and Asian bacteria
This Asian bacterium, christened CLas, is “the one that causes the most damage, causing tree deaths very quickly,” stresses Bernard Reynaud, lead author of the study.
“If the Asian disease (in Europe) returns, we risk a major pandemic”
Researchers previously thought that the disease in its ‘Asian’ form could only be transmitted by the Asian flea, Diaphorina citri, and its ‘African’ form only by the African flea, Trioza erytreae. But after testing on Reunion Island, the only area where the two species coexist, the CIRAD team concluded that the African flea was “such an effective vector” for transmission of the Asian bacterium, concludes Bernard Reynaud .
3 Closer to the Mediterranean
“If the Asian disease returns (to Europe), we risk a major pandemic,” he warns, knowing the means to combat it are inadequate. Especially since the CLas bacterium was recently spotted in Ethiopia and Kenya, closer than ever to the Mediterranean basin.
The researchers therefore recommend increased surveillance to avoid bringing in contaminated plant material (citrus plants, slips), with controls, possible quarantines and early detection in suspected cases.
4 ways to contain the disease
CIRAD’s work aims in particular to develop resistant varieties. Some species, like the lemon caviar native to Oceania, are able to resist the bacteria. Transplantations and hybridizations are investigated by identifying resistant genes.