Improving strategies to combat the decline of lavender and lavandin

Lavender and lavandin are iconic crops of Haute Provence, which have been suffering from a decline in recent decades. The aetiological agent responsible for this decline is the Stolbur phytoplasma, and the main vector for this phytoplasma is the leafhopper Hyalesthes obsoletus. A sensitive and reliable diagnostic technique has been developed, enabling the certification of plant material produced in accordance with the ‘healthy plants’ specifications to be guaranteed. A large-scale epidemiological study showed that the plots were infected by 16 different genotypes of the Stolbur phytoplasm, and that the disease spread mainly from lavender plant to lavender plant, and from lavender field to lavender field. Finally, the study of tolerance showed that susceptibility to dieback is not linked to the plant-phytoplasm relationship, but more likely to the interaction between the leafhopper and the plants. This leafhopper is present in all cultivated plots, but in highly variable numbers. AFLP genotyping also showed that the genetic diversity of wild lavender was fairly limited, and that genetic selection carried out by the industry had reduced it very slightly.