Pathogenicity of Xanthomonas translucens from Annual Bluegrass on Golf Course Putting Greens

Bacterial wilt of Poa annua has been seen increasingly in the Northeast and mid-Atlantic United States in the past few years. The disease causes severe injury to putting greens and can kill large stands of turfgrass. For some time, however, both the bacterial origin of the disease and the causal agent were in doubt. In order to investigate the identity of the causal agent, isolation of the pathogen was undertaken and pathogenicity was confirmed using Koch's postulates on P. annua. Additional pathogenicity trials then were undertaken to determine the host range of the causal bacterium. Ability of the bacterium to cause disease was restricted to P. annua var. annua and P. attenuata. However, the bacterium was able to survive asymptomatically in vascular systems of P. annua var. reptans and P. trivialis. Experiments to determine the optimal growth temperature of the organism demonstrated that the bacterial growth peaked between 30 and 35°C. Fatty acid analysis suggested that the bacterium might be a species of Xanthomonas but was inconclusive. Ribosomal RNA analysis demonstrated significant similarity to the American Type Culture Collection isolate of Xanthomonas translucens pv. poae at 99.8%. Comparison of the host range to previously reported data agrees with our molecular findings and indicates that the likely casual organism of bacterial wilt of annual bluegrass is X. translucens pv. poae.