Transmission efficiencies of two strains of Xylella fastidiosa from culture by glassy-winged sharpshooters and the evaluation of a novel xylem vessel inoculation system

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), is an invasive, xylem-feeding insect that transmits of Xylella fastidiosa (Wells) (Xf), the causal agent of Pierce's Disease (PD) of grapevine and other plant diseases. Transmission of Xf occurs when the insect inserts its stylets into the plant's xylem vessels. Competition by different strains of Xf for space to colonize the foregut of the insect can impact the ability of an insect to be a proficient vector. In order to evaluate if biofilm formation by the PD strain is negatively impacted by an presence of a non-PD strain, we inoculated GWSS with various combinations of Xf strains. It was found that the antecedent Xf strain was likely to become dominant in the foregut of GWSS and suppress of the biofilm formation of strains that colonized later. Additionally, a xylem vessel inoculation system for placing Xf in the plant's xylem vessels for acquisition was needed to study transmission pattern of different Xf subspecies. Therefore, we developed two xylem vessel inoculation systems; a transpiration system and an injection system, to determine the parameters of competition between strains within the foregut of the sharpshooter.