Impact of alfalfa mosaic virus subgroup I and II isolates on terpene secondary metabolism of Lavandula vera D.C., Lavandula x alardii and eigth cultivars of L. hybrida Rev.

Lavandula vera D.C., Lavandula X alardii and eight different L. hybrida Rev. cultivars cultivated at the Herb Garden of Casola Valsenio (Italy) were found naturally infected by Alfalfa mosaic virus (AMV). The viral disease, consisting of a “yellow mosaic” on leaves and stems, was identified by means of electron microscopy, RT-PCR-RFLP and PAS-ELISA assays. Four of the AMV isolates were molecular characterized by determining the nucleotid and aminoacid sequences of the coat protein. Phylogenetic relationships suggested that three of them belonged to subgroup I (from cvs. Ordinario and Grosso, Lavandula X alardii), while the isolate from cv. Sumiens showed molecular features of subgroup II. These results confirm the spread in Italy of AMV isolates belonging to subgroup I; the “Sumiens” isolate of subgroup II has been probably introduced with infected vegetative propagation material. By means of GC/GC-MS, the influence of the “yellow disease” on essential oil biosynthesis and quality was verified. The infection of Lavandula plants by AMV (of the two subgroups) was found to decrease essential oil secretion. Changes in the relative composition regarded the linalool-linalyl acetate ratio, the overall increase in terpenic esters and in some cases an increased sesquiterpenic abundance. The importance of the phytopathological status of essential oil bearing crops is outlined.