UC Berkeley

Xylella fastidiosa was the first bacterial plant pathogen to have its whole genome sequenced. Nonetheless, the scientific community remains uncertain about the mechanism by which this pathogen causes disease. The determinants of its host range are largely unknown. While as a species, X. fastidiosa can infect hundreds of plants, any individual strain’s potential hosts cannot be predicted. This dissertation is an interrogation of host specificity at three vastly different scales. The research is ordered from broad to narrow, beginning with a global analysis. I computationally modeled pathogen host range using 23 plant genera. Through this breadth, I was able to find correlations between hosts and genome content, as well as make estimates for likely ancestral hosts at internal phylogenetic nodes. My second chapter compares strains from Central America with strains introduced into the United States. I show that the introduced pathogen population is poor at infecting an ancestral host. I also found a suite of genes in the introduced population associated with the host jump. Finally, I dive into disease progression in one host species grown in Northern California, Vitis vinifera. Over the course of three years, I documented how disease development can vary among grapevine cultivars. This final chapter provides suggestions for disease management through more accurate detection of X. fastidiosa in an agricultural setting. The overarching goal of these works is to improve our understanding of the determinants of host specificity and disease progression of the economically and environmentally important pathogen species Xylella fastidiosa.