ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 95 Special Issue 2, October 2018
Population shifts in bacterial spot-causing Xanthomonas in Florida tomato (Lycopersicon escultenum Mill.)
Tomato is a widely cultivated fruit crop in the United States. Florida is the largest producer of fresh-market tomato in the U.S. Bacterial spot is a consistent threat to production of tomato. Successful disease management is limited due to shifts in bacterial populations over time and the development of resistance against commonly used bactericides. Surveys over recent years recovered Xanthomonas perforans in Florida. Prior to the introduction of tomato race 3 (T3) X. perforans strains into Florida in 1991, only X. euvesicatoria tomato race 1 (T1) strains were prevalent. X. perforans was shown to produce bacteriocins antagonistic to X. euvesicatoria strains. In the late 1990s, the X. perforans population in Florida shifted from T3 to T4. Using multilocus sequence analysis, we observed considerable variation in X. perforans population, with evidence for recombination events between X. perforans and X. euvesicatoria. Based on whole genome sequencing of representative strains collected, we observed notable changes in effector profiles of X. perforans strains. For example, the effector, avrXv3, specific to T3, is non-functional in T4 strains and is not recognized by the corresponding tomato R gene. Interestingly, effectors xopJ4 and avrBs2 are conserved throughout this population, while avrBsT has become well established in the recent bacterial population. These conserved effectors are potential targets for resistance breeding efforts in tomato.
Keywords: Xanthomonas, tomato, species population shifts, molecular phylogeny