P-473 - Urban Ecology of Xylella fastidiosa in Southern California

Xylella fastidiosa is a xylem-limited pathogenic bacterium with a host range exceeding 800 plant species. The introduction of the glassy-winged sharpshooter (Homalodisca vitripennis) to Southern California in the late 1990’s led to an increase in X. fastidiosa infections in tree species commonly planted in urban and suburban areas. There is currently limited insight into what genotypes of X. fastidiosa are causing disease in Southern California urban forests. A systematic field survey was used to characterize the genetic diversity and spatial distribution of X. fastidiosa in street trees in Southern California.Street trees in San Diego and Los Angeles counties were sampled in 2023 and 2024. Stem and leaf tissue were collected from all trees with observable symptoms. Total genomic DNA was extracted from these samples; 532 trees were sampled in total. Isolation of the bacteria in pure culture was repeatedly attempted as well. Approximately 30% of all samples tested positive for X. fastidiosa, significantly higher than other studies with similar approaches. Sweetgum (Liquidambar styraciflua), purple-leaf plum (Prunus cerasifera), Pohutukawa (Metrosideros excelsa), and olive (Olea europaea) frequently exhibited symptoms. Two X. fastidiosa subspecies have been detected in the region so far: X. fastidiosa subsp. multiplex and X. fastidiosa subsp. sandyi (in olive trees). Distinct sequence types (STs) were observed across host species. Our findings suggest that tree-associated X. fastidiosa is more prolific and genetically diverse in Southern California than previously considered.