The influence of three Prunus rootstocks-a domestic plum, a domestic peach, and a peach from Brazil-on the occurrence of the vector of phony peach disease, Homalodisca coagulata, was assessed in a 4-yr study in an experimental block of Flordaking peach (P. persica). Relationships between the amino acid profile of xylem fluid from scions, the concentration of Xylella fastidiosa in xylem fluid from roots, and leafhopper occurrence were also assessed. The vector was less numerous in trees on the Brazilian rootstock than in those on the domestic rootstocks. The concentration of the bacterium in root xylem fluid was lower in the peach rootstocks than in the domestic plum. The occurrence of the leafhopper, the amino acid profile of scion xylem fluid, and the concentration of X. fastidiosa were influenced by the rootstock. The amino acid profile of xylem fluid was not correlated with the concentration of X. fastidiosa in root xylem fluid.