Production of Diagnostic Symptoms of Blight in Citrus Inoculated with Xylella fastidiosa

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Abstract
Strains of Xylella fastidiosa, a xylem-limited, gram-negative bacterium isolated from various natural hosts in Florida [USA], were used to inoculate rooted cuttings of rough lemon (Citrus jambhiri) seedlings, the rootstock that is most susceptible to citrus blight. Eighteen to 24 mo later, stunting and dieback symptoms were observed in rooted cuttings inoculated with X. fastidiosa strains obtained from citrus, oak (Quercus spp.), grapevine (Vitis spp.), goldenrod (Solidago fistulosa), blackberry (Rubus sp.), and peach (Prunus persica). One X. fastidiosa strain obtained from citrus produced stunting and dieback symptoms in rough lemon, rangpur lime (C. limonia), and sweet orange (C. sinensis) seedlings. Compared with healthy controls, inoculated seedlings also had reduced water conductivity in stem sections and elevated zinc levels in trunk wood and bark, which are diagnostic tests for citrus blight. Five of nine trees of the sweet orange cultivar Pineapple on rough lemon rootstock developed visible blight symptoms and had reduced water conductivity in stem selections. One of these trees had the complete blight syndrome: stunting, smaller and more upright leaves, dieback to near the bud union, zinc deficiency in the leaves, xylem dysfunction, elevated water-soluble phenolic levels, and elevated zinc levels in the bark. Thus, X. fastidiosa can produce blight symptoms in citrus.