Settling and feeding behavior of sharpshooter vectors on plum genotypes with different susceptibility levels to leaf scald disease (Xylella fastidiosa)

Plum leaf scald (PLS) is a serious disease caused by Xylella fastidiosa subsp. multiplex, a pathogenic bacterium transmitted by insects with specialized xylem feeding (Hemiptera, Cicadellidae, Cicadellinae). In Brazil, the development of plum genotypes that apparently are not infected under field conditions has opened new prospects for disease control based on host plant resistance. As example, the 'SC13' and 'SC7' genotypes can not be infected under field conditions, although 'SC13' is infected by graft inoculation. So, we hypothesize that the performance of genotypes in the field may be related to the vector behavior. To clarify the possible relation of the genotype with the vector behavior we investigated the settling preference and xylem sap ingestion rates of the sharpshooter leafhoopers Bucephalogonia xanthophis Berg (1879) and Sibovia sagata Signoret (1854) (Hemiptera, Cicadellidae, Cicadellinae), as well as the probing behavior of B. xanthophis using the Electrical Penetration Graph (EPG) technique, on two Japanese plum genotypes ('SC7', 'SC13') contrasting with 'Laetitia' (susceptible to PLS). In the settling experiments, 'SC7' was less preferred by both vector species. 'SC13' did not affect settling, but reduced sap ingestion rates of S. sagata and also affected stylet activities of B. xanthophis, by increasing the duration of waveforms N (interruption of sustained ingestion during xylem phase), and the number of Xi and decreasing the duration of waveform Xi (active xylem sap ingestion). The results of settling and feeding behavior of the sharpshooters suggest that vector-plant interaction aspects are likely involved in the variation of disease intensity in the field.