Location, transmission, and impact of Xylella fastidiosa in southern highbush blueberries
Holland, Renee Marie
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Bacterial leaf scorch is an emerging disease of southern highbush blueberry caused by the xylem-limited bacterium Xylella fastidiosa. This thesis investigated 1) the distribution of the pathogen in stem and root sections of naturally infected blueberry plants; 2) the level of disease transmission through vegetative propagation; and 3) the association between disease resistance and xylem hydraulic conductance in three blueberry cultivars. The pathogen was detected readily in xylem sap from lower stem sections of affected plants, and as disease severity increased, bacterial titer increased in sections of all age classes, particularly root sections. Disease transmission through softwood cuttings from symptomatic mother plants was low but non-negligible (5.1% average). Emerald, a field-resistant cultivar, had higher levels of xylem hydraulic conductance than the susceptible Star and FL 89-16. In diseased plants of FL 89-16, petiole conductance was reduced significantly, potentially explaining the high propensity for leaf scorch-related plant death in this cultivar.