First Report of Subanguina radicicola, the Root-Gall Nematode Infecting Poa annua Putting Greens in Washington State.

In the fall of 2006, a golf course in Snoqualmie, WA renovated five putting greens with commercially produced Poa annua L. sod from British Columbia, Canada. Prior to the renovation, the greens had been planted with Agrostis stolonifera L. cv. Providence, which was removed during the renovation. In February of 2007, chlorotic patches were observed on the newly established P. annua greens. When the roots were examined, extensive galling was observed throughout plant roots. Galls were slender and twisted in appearance and less than one millimeter long. Upon dissection of washed galls, hundreds of eggs were exuded into the surrounding water droplet and both mature male and female nematodes were observed. Further morphometric examination of males, females, and juvenile nematodes demonstrated that they were Subanguina radicicola (Greef 1872) Paramanov 1967 (1). Amplification of nematode 18S, ITS1, and 5.8S regions, using previously published primers (2), resulted in a 100% sequence match with the publicly available sequence for S. radicicola, GenBank Accession No. AF396366. Each P. annua plant had an average of six galls (with a range of 1 to 8), primarily located within the top 2 cm of the soil. All five new P. annua putting greens at the golf course were infested with the nematode. Additionally, P. annua from two A. stolonifera cv. Providence greens that had not been renovated was infected, suggesting that the population occurred onsite and was not imported from the Canadian sod. S. radicicola has been identified as causing severe damage in New Brunswick, Canada on P. annua putting greens and in wild P. annua in the northwestern United States, but to our knowledge, this is the first report of the nematode affecting P. annua on a golf course in the United States. References: (1) E. L. Krall. Wheat and grass nematodes: Anguina, Subanguina, and related genera. Pages 721-760 in: Manual of Agricultural Nematology. Marcel Dekker, New York, 1991. (2) N. A. Mitkowski et al. Plant Dis. 86:840, 2002.

Population Dynamics of Plant-Parasitic Nematodes in Golf Course Greens Turf in Southern New England.

The distribution, frequency, and population levels over time of plant-parasitic nematodes were surveyed on 114 greens from 38 different golf courses throughout southern New England. Sampling took place in the spring, summer, and fall of 2003 and 2004. The predominant genera of phytoparasitic nematodes recovered from soil samples were Tylenchorhynchus, Helicotylenchus, Criconemella, Hoplolaimus, and Heterodera. Tylenchorhynchus and Helicotylenchus spp. were the most common, found in all 38 golf courses sampled. Population levels were significantly higher (α = 0.05) in 2004 than in 2003 for Criconemella, Tylenchorhynchus, and Heterodera juveniles. There was a significant effect of season on population levels of Criconemella, Tylenchorhynchus, and Heterodera juveniles in the 2003 sampling year, and on Helicotylenchus, Tylenchorhynchus, and Heterodera juveniles in 2004. Population levels were highest in the fall for all genera except for Tylenchorhynchus, which were highest in the summer for both years. The results of this study suggest that parasitic nematodes are present in relatively high numbers in golf course turf soils in southern New England, and that there are variations in the dynamics of population levels among the different genera found in the area.

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.

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.

Subanguina radicicola, the Root-Gall Nematode Infecting Poa annua in New Brunswick, Canada.

Poa annua frequently is found as the dominant turfgrass species on golf course putting greens grown in the range of cool-season grasses. While not intentionally established, it is an aggressive weed in stands of bentgrasses (Agrostis spp.). When significant encroachment of P. annua occurs, it often is maintained indefinitely. In May 2003, P. annua putting greens at the Riverside Country Club in Rothesay, New Brunswick, Canada showed signs of an unidentified disease. Putting greens were slow to green up and large chlorotic patches were evident across affected areas. When roots were examined, extensive galling was observed. Galls were slender and often twisted in appearance. Upon dissection of washed galls, hundreds of eggs were exuded into the surrounding water droplet, and mature male and female nematodes were observed. Further morphological examination of males, females, and juvenile nematodes demonstrated that they were Subanguina radicicola (Greef 1872) Paramanov 1967 (1,2). Each P. annua plant had an average of four galls (with a range of two to nine) primarily located within the uppermost centimeter of the soil. Of 18 P. annua putting greens, four were affected by the nematode and displayed the same damage symptoms. S. radicicola has been identified from American beachgrass in Rhode Island and from P. annua in Oregon, but to our knowledge, this is the first report of the nematode affecting P. annua on a golf course in eastern North America. References: (1) W. F. Mai and P. Mullin. Plant-Parasitic Nematodes: A Pictorial Key to Genera. Cornell University Press, Ithaca, New York, 1996. (2) G. Thorne. Principles of Nematology. McGraw-Hill Book Company, Inc., New York, 1961.

First Report of Leaf and Sheath Spot Caused by Rhizoctonia zeae Affecting Panicum tennesseense in Rhode Island.

Panicum tennesseense Ashe is a perennial, coarse-textured, cool-season grass (similar in appearance to many warm-seasoned grasses), which grows in the southern coastal areas of New England and is commonly found in home lawns, roadsides, and meadows. In August 2002, a large stand of P. tennesseense with significant leaf spotting was identified in Washington County, RI. Lesions were excised, surface sterilized with 0.6% sodium hypochlorite, and plated on one-half-strength potato dextrose agar (PDA). Cultures were incubated at 25°C, and mycelia quickly covered plates within 3 days. After 2 weeks in darkness, plates were covered with white, aerial mycelium. When placed under near-UV light, no aerial mycelium was produced, and mycelia were a salmon color. After 5 weeks, separate, spherical, 0.5-mm-diameter beige sclerotia were produced submerged throughout the media and turned red within a few days. Sclerotia were not produced in the absence of near-UV light. Spores were not produced, and right-angled branching, characteristic of Rhizoctonia spp., was observed. Monilioid hyphae were also produced in culture. At the optimal growth temperature of 32°C, mycelia grew an average of 33.6 mm/day. Cells were stained using safranin, and the number of nuclei observed within young hyphal cells was five or seven. On the basis of the described mycelial and sclerotial characterisitics, the isolated fungus was identified as Rhizoctonia zeae (1,2). To demonstrate pathogenicity, plugs of isolated fungi were cut from PDA plates, placed on leaf blades at the junction with leaf sheaths, and incubated in a greenhouse humidity chamber at an average temperature of 32°C and 80% humidity. After 3 days, significant disease was observed and included blighting of newly emerged shoots, blighting and spotting on leaf sheaths, and severe spotting on leaf lamina. Whereas Rhizoctonia solani has been reported as a pathogen on P. tennesseense, to our knowledge, this is the first report of R. zeae induced leaf and sheath spot on this host (1). References: (1) H. Couch. Diseases of Turfgrasses. Krieger Publishing Co., Malabar, FL, 1995. (2) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St. Paul, MN. 1991.

Soil organic matter and management of plant-parasitic nematodes.

Organic matter and its replenishment has become a major component of soil health management programs. Many of the soil's physical, chemical, and biological properties are a function of organic matter content and quality. Adding organic matter to soil influences diverse and important biological activities. The diversity and number of free-living and plant-parasitic nematodes are altered by rotational crops, cover crops, green manures, and other sources of organic matter. Soil management programs should include the use of the proper organic materials to improve soil chemical, physical, and biological parameters and to suppress plant-parasitic nematodes and soilborne pathogens. It is critical to monitor the effects of organic matter additions on activities of major and minor plant-parasitic nematodes in the production system. This paper presents a general review of information in the literature on the effects of crop rotation, cover crops, and green manures on nematodes and their damage to economic crops.

Characterization of Root-Knot Nematode Populations Associated with Vegetables in New York State.

The northern root-knot nematode (Meloidogyne hapla) causes significant damage on vegetables in New York State. This study was conducted to determine if other species of Meloidogyne are also present in New York vegetable fields and to better characterize the root-knot populations in order to facilitate the development of effective rotations for nematode management. Populations of Meloidogyne were collected from 18 vegetable fields across New York and maintained in the greenhouse on tomato cv. Rutgers as both field populations and single-female populations. For the purposes of species identification, nematodes from each population were examined using perineal pattern analysis, scanning electron microscopy, and cytological analysis. All techniques identified the presence of only Meloidogyne hapla in the collected samples. The host range of the populations of Meloidogyne that were collected was investigated using a modified form of the North Carolina Differential Host Test. While host ranges were variable among the collected populations, the host range of all populations closely corresponded to that of M. hapla. The internal transcribed spacer region (ITS1) of the collected populations was amplified and sequenced. All sequences from the collected populations corresponded to the published sequence of M. hapla. Based on these results, it was concluded that M. hapla is the only root-knot nematode species present in New York vegetable fields. Crop rotational strategies for management of the root-knot nematode on vegetables in New York should be devised to reflect this fact.