First Report of Bacterial Wilt of Annual Bluegrass Caused by Xanthomonas translucens pv. poae in Montana.

During August 2003, a golf course putting green sample composed of Poa annua from the Buffalo Hill Country Club in Kalispell, MT exhibiting symptoms of general decline, wilting, and necrosis was submitted to the University of Rhode Island Turfgrass Disease Diagnostic Laboratory. No pathogenic fungi were observed or cultured from affected plants. Bacterial streaming was observed from cut leaves. Cut leaves were surface disinfested for 5 min in a 0.6% sodium hypochlorite solution and plated on yeast dextrose calcium carbonate (YDC) agar media. A single yellow, mucoid colony type composed of rod-shaped bacteria was isolated from all leaves. Bacteria were gram negative, lacked anaerobic growth, did not fluorescence on King's medium B, and were able to grow at 33°C on YDC. Colonies were transferred to YDC for 10 days, DNA was extracted and a 2,190-bp region encompassing the 16S rRNA, ITS, and 5' end of the 23S rRNA was amplified via polymerase chain reaction (PCR) using previously published protocols (1). Sequence comparisons of the resulting 2,190-bp PCR product revealed a 99.7% sequence similarity with X. translucens pv. poae (American Type Culture Collection [ATCC] no. 33804) and a 99.8% sequence similarity with X. translucens pv. poae M-1 (Torrington, CT). No higher sequence similarity could be identified from a BLAST search. The Montana isolate and the previously described M-1 isolate were inoculated onto four replicates of 5-month-old P. annua var. annua plants by dipping cut leaves into a bacterial suspension adjusted to 10⁹ CFU/ml in 0.9% NaCl. Control plants were dipped into 0.9% NaCl without the presence of the bacteria. All plants were placed in the greenhouse at an average daytime temperature of approximately 24°C and 12 h of sunlight. After 8 weeks, the plants were assessed for disease and checked for bacterial streaming. This experiment was repeated once. The Montana isolate caused approximately 68 and 70% leaf death and the M-1 isolate caused 21 and 25% leaf death in the two experiments. Bacterial streaming was observed in approximately 50 and 80% of the examined leaves inoculated with the M-1 and Montana isolates, respectively. Control plants showed no leaf mortality or bacterial streaming. Although this pathogen was originally identified in the United States in Michigan (2) and has been prevalent in the northeastern United States for the past 10 to 15 years, to our knowledge, this is the first report of the disease in the northwestern United States. References: (1) N. A. Mitkowski et al. Plant Dis. 89:469, 2005. (2) D. L. Roberts et al. Phytopathology 75:1289, 1985.