Grapevine Pierce's disease bacterium now called Xylella fastidiosa; it attacks other hosts as well as grapevine
Grapevine Pierce's disease bacterium is a quarantine pest on the EPPO Al List (N° 166). Although a fastidious prokaryote, it has now been cultured and accordingly characterized as a bacterium. Wells et al. (1987) have named it Xylella fastidiosa.
X. fastidiosa is primarily known as the pathogen responsible for Pierce's disease of grapevine. The same pathogen can also be transmitted to almond (causing leaf scorch) and to lucerne (causing dwarf disease). Hopkins & Adlerz (1988) note that the bacterium can be isolated from numerous mostly symptomless hosts (of at least 28 families), among the natural wild vegetation of areas where Pierce’s disease is recorded. Some of the isolates infect grapevine while others do not, so that bacteria identifiable in culture as X. fastidiosa may belong to strains differing in host specificity (pathovars?).
Indeed, other diseases previously attributed to distinct pathogens are now considered to be caused by strains of X. fastidiosa: in particular, peach phony disease bacterium (EPPO Al List), plum leaf scald, periwinkle wilt, oak leaf scorch, mulberry leaf scorch, sycamore leaf scorch.
One particularly important case is "citrus blight". Hopkins (1988) has shown that characteristic symptoms of this disease, previously of uncertain aetiology, can be obtained by inoculation of Citrus jambhiri cuttings (a highly susceptible rootstock) with certain strains of X. fastidiosa.
However, full proof (Koch 's postulates) is still lacking that the disease is really caused by X. fastidiosa.
Further studies on host specificity of strains are needed to clarify which present a danger to the EPPO region.
Sources
Hopkins D.L. & Adlerz W.C. (1988) Natural hosts of Xylella fastidiosa in Florida. Plant Disease 72, 429-431.
Hopkins D.L. (1988.) Production of diagnostic symptoms of blight in citrus inoculated with Xvlella fastidiosa. Plant Disease 72, 432-435
Wells J.M., Raju B.C., Hung H.Y., Weisburg W.G., Mandelco-Paul L. & Brenner D.J. (1987) Xylella fastidiosa gen. nov; sp. nov.: Gram-negative, xylem-limited fastidious plant bacteria related to Xanthomonas spp. International Journal of Systematic Bacteriology 37, 136-43.