Oranges and lemons are in danger. In the event of the combined presence of an insect, already present in Europe, and an Asian bacterium devastating for citrus fruits, they would run a “major risk” of an epidemic of the “yellow dragon”, warn researchers in a study published at the end of December in the journal Borders.
Currently, this Huanglongbing disease (HLB) is the deadliest for these fruits in the world, according to the Center for International Cooperation in Agricultural Research for Development (CIRAD), based in France, which coordinated this work.
Asian bacterium “does the most damage”
Since the 2000s, it has decimated the crops of major producers such as China or the United States, forced to use massive amounts of antibiotics and insecticides. Europe had been spared until then. But a team of researchers has discovered that a tiny insect observed for five years in Spain and Portugal, the African psyllid Trioza erytreae, could transmit the agent at the origin of the severe form of HLB.
Among several strains, this Asian bacterium, called CLas, is “the one that does the most damage, causing very rapid death of trees”, underlines Bernard Reynaud, lead author of the study and director of a CIRAD research unit. University of Reunion.
Researchers previously thought that the disease in its “Asian” form could only be transmitted by the Asian psyllid, Diaphorina citri, and that its “African” form could only be carried by the African psyllid, Trioza erytreae.
Surveillance, controls and quarantines
The CIRAD team, which is part of the European PRE-HLB disease control consortium, therefore compared their transmission rates on Reunion Island, the only territory where the two species of psyllids and the CLas bacterium coexist. These tests made it possible to demonstrate that the African psyllid “was such an effective vector” for transmitting the Asian bacterium, concludes Bernard Reynaud.
“If the Asian disease returned to Europe, we would risk a major pandemic”, knowing that the means of control are not suitable, he warns. The CLas bacterium was recently spotted in Ethiopia and Kenya, closer than ever to the Mediterranean.
The researchers therefore recommend strengthening surveillance to avoid the introduction of contaminated plant material (citrus plants, grafts), with control, possible quarantines, and early detection in the event of suspicion.