Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2018
Publication Date: 12/1/2018
Citation: Stenger, D.C., Burbank, L.P., Krugner, R., Sisterson, M.S. 2018. Genotyping Xylella fastidiosa present in the glassy-winged sharpshooter in the General Beale area of Kern County, California. CDFA Pierce's Disease Control Program Research Symposium. p. 140.
Technical Abstract: During 2016 and 2017, glassy-winged sharpshooters (GWSS) collected from vineyards or nearby citrus orchards in the General Beale Area of Kern County were assessed for X. fastidiosa (Xf) infection by real-time PCR using total DNA samples extracted from GWSS heads. Of 1031 insects, 154 (15%) tested positive for Xf. A subset of Xf-positive GWSS DNA samples were subjected to multi-locus sequence typing to determine Xf genotypes associated with GWSS. Conventional PCR products for three genes (petC, leuA, and holC) were cloned and sequenced. Cloned sequences were assigned to Xf subspecies based on SNP signatures (7-12 polymorphic sites per gene that differentiate reference genomes of subspecies fastidiosa and multiplex). Of 1821 MLST clones sequenced, 1365 were genotyped as subspecies fastidiosa and 446 as subspecies multiplex. Of cloned subspecies fastidiosa sequences, 97% had SNP signatures identical to the corresponding gene present in 24 Xf subspecies fastidiosa strains cultured from Pierce’s disease affected vines sampled in 2016 and 2017. Presence of SNP signatures representing both subspecies in one or more cloned genes was commonly observed within individual GWSS. This observation indicates that genetic complexity of Xf in many insects was greater than one due to mixtures of two subspecies or mixtures of two genotypes of one subspecies in which a proportion of the population was derived from a lineage with a history of horizontal gene transfer and homologous recombination. Inferences drawn from these conclusions suggest that 1) individual GWSS visit multiple host species (inoculum sources); 2) multiple acquisition events may be separated in time and space; 3) competitive exclusion of Xf in the foregut is weak or not operating; and 4) the vector foregut represents a potential arena for exchange of genetic material among sympatric X. fastidiosa subspecies.