Intersubspecific Recombination in Xylella fastidiosa Strains Native to the United States: Infection of Novel Hosts Associated with an Unsuccessful Invasion

Abstract

ABSTRACTThe bacterial pathogenXylella fastidiosainfects xylem and causes disease in many plant species in the Americas. Different subspecies of this bacterium and different genotypes within subspecies infect different plant hosts, but the genetics of host adaptation are unknown. Here we examined the hypothesis that the introduction of novel genetic variation via intersubspecific homologous recombination (IHR) facilitates host shifts. We investigated IHR in 33X. fastidiosasubsp.multiplexisolates previously identified as recombinant based on 8 loci (7 multilocus sequence typing [MLST] loci plus 1 locus). We found significant evidence of introgression fromX. fastidiosasubsp.fastidiosain 4 of the loci and, using published data, evidence of IHR in 6 of 9 additional loci. Our data showed that IHR regions in 2 of the 4 loci were inconsistent (12 mismatches) withX. fastidiosasubsp.fastidiosaalleles found in the United States but consistent with alleles from Central America. The other two loci were consistent with alleles from both regions. We propose that the recombinant forms all originated via genomewide recombination of oneX. fastidiosasubsp.multiplexancestor with oneX. fastidiosasubsp.fastidiosadonor from Central America that was introduced into the United States but subsequently disappeared. Using all of the available data, 5 plant hosts of the recombinant types were identified, 3 of which also supported non-IHRX. fastidiosasubsp.multiplex, but 2 were unique to recombinant types from blueberry (7 isolates from Georgia, 3 from Florida); and blackberry (1 each from Florida and North Carolina), strongly supporting the hypothesis that IHR facilitated a host shift to blueberry and possibly blackberry.