Transmission of Xylella fastidiosa subsp. pauca to olive trees by sharpshooters and spittlebugs common in Brazilian orchards

The vector-borne bacterium, Xylella fastidiosa subsp. pauca, has been isolated from olive trees showing olive quick decline syndrome (OQDS) symptoms in different locations of Southeastern Brazil, but the vectors spreading this putative pathogen are unknown in that region. In other crops, this bacterium is transmitted by xylem-sap feeding leafhoppers (sharpshooters) (Hemiptera: Cicadellidae: Cicadellinae) and spittlebugs (Hemiptera: Cercopoidea). In this study, we showed that 11 sharpshooter and three spittlebug species common in olive orchards of the Mantiqueira Mountain Range Region, Southeastern Brazil, are able to transmit X. fastidiosa subsp. pauca to olive trees. For the transmission assays, field-collected or laboratory-reared adults of each species were first pretested for natural infectivity by confinement with sleeve cages on healthy seedlings of Catharanthus roseus during an inoculation access period (IAP) of 12 h (10-20 insects/plant). After the pretest, the insects were confined with sleeve cages on potted olive trees (cv. Grappolo) infected with X. fastidiosa subsp. pauca (sequence type 16) for an acquisition access period of 24 h, followed by a 24-h IAP on potted healthy olive trees cv. Koroneiki (3-10 insects/plant, depending on the sharpshooter/species) in a protected screenhouse. About 3-5 healthy C. roseus (pretest) and olive (test) plants were not exposed to insects (negative control). All pretest and test plants were assayed by real time PCR at 12 months after inoculation. Estimated transmission rates by single insects (based on 2-3 trials) ranged from 0.4-12.9%. The following vector species (and transmission rates, when applicable) were identified: the spittlebug Notozulia entreriana (9.2%), and the sharpshooters Erythrogonia phoenicia (1.6%), Erythrogonia sp. 1 (4.8%), Macugonalia cavifrons (1.8%), Macugonalia leucomelas (1.7%), Oragua sp. 1 (0.4%), Plesiommata sp. 1, Scopogonalia paula (12.9%), Sibovia sagata (0.7%) and Sonesimia grossa (0.5%). None of them transmitted the bacterium in the pretest assay.

Keywords:  Olea europea, Xylem-limited bacterium, vector range. 

Support: Horizon 2020 (XF Actors 727987), Fapesp (Proc. 2016/02176-7), Capes and CNPq/Brazil (Proc. 310554/2016-0).