N. A. Mitkowski

Identification, Characterization, and Distribution of Acidovorax avenae subsp. avenae Associated with Creeping Bentgrass Etiolation and Decline

Bacterial etiolation and decline caused by Acidovorax avenae subsp. avenae is an emerging disease of creeping bentgrass (Agrostis stolonifera) in and around the transition zone, a unique area of turfgrass culture between cool and warm regions of the United States. It is suspected that the disease has been present for many years, although diagnosis of the first occurrence was not reported until 2010. Solicitation of samples from golf courses in 2010 and 2011 was undertaken to investigate the prevalence and dissemination of Acidovorax avenae subsp. avenae on creeping bentgrass. At least 21 isolates from 13 states associated with these outbreaks on golf courses were confirmed as A. avenae subsp. avenae by pathogenicity assays and 16S rDNA sequence analysis at two independent locations. Pathogenicity testing of bacterial isolates from creeping bentgrass samples exhibiting heavy bacterial streaming confirmed A. avenae subsp. avenae as the only bacterium to cause significant disease symptoms and turfgrass decline. Host range inoculations revealed isolates of A. avenae subsp. avenae to be pathogenic on all Agrostis stolonifera cultivars tested, with slight but significant differences in disease severity on particular cultivars. Other turfgrass hosts tested were only mildly susceptible to Acidovorax avenae subsp. avenae infection. This study initiated research on A. avenae subsp. avenae pathogenicity causing a previously uncharacterized disease of creeping bentgrass putting greens in the United States.

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 Kochs 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.

Nematodes associated with vineyards throughout Markazi Province (Arak), Iran

In a survey conducted from April 2008 through October 2008, 21 nematode species were found associated with grapes in Markazi Province, Iran. These included: Aphelenchus avenae, Aphelenchoides limberi, Boleodorus thylactus, Criconema mutabile, Mesocriconema xenoplax, Ditylenchus myceliophagus, Irantylenchus clavidorus, Helicotylenchus digonicus, H. vulgaris, H. crenacauda, H. pseudorobustus, Hemicriconemoides mangiferae, Meloidogyne javanica, Geocenamous brevidens, G. rugosus, Pratylenchus neglectus, P. thornei, P. ritteri, Tylenchulus semipenetrans, Xiphinema index and Zygotylenchus guevarai. Populations varied in their frequency and distribution among surveyed vineyards but Helicotylenchus spp. and Pratylenchus spp. were the most commonly observed genera. Meloidogyne spp. and Xiphinema spp. were rarely encountered during the survey. This is the first reported province-wide nematode survey of grapes in Iran. Morphological and morphometric variations that typified the survey populations are given and discussed for certain nematode species.

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.

Chemical Methods of Moss Control on Golf Course Putting Greens

Many golf courses throughout the United States are perennially affected by moss encroachment. Unfortunately, moss control products must often be applied at regular intervals throughout the season and can be very phytotoxic. In addition, application timing impacts efficacy. Copper in the form of copper hydroxide + mancozeb (Junction) can control moss when applied on a biweekly basis at 0.2 lb/1000 ft² with minimal phytotoxicity. Season-long application may be required on heavily infested greens and fall applications are often most effective. Higher rates can severely damage turf. Silver nitrate is extremely effective at eliminating moss infestations in 1 to 2 applications at 0.275 lb/1000 ft² without phytotoxicity. However, silver is currently not labeled as a pesticide. Carfentazone (Quicksilver) has been labeled for use against moss and appears to be very effective in reducing up to 90% of moss when applied twice at a 14-day interval of 6.7 oz/acre [* see erratum]. Terracyte applied at 14-day intervals at no more than 8 lb/1000 ft² can also successfully combat a moss infestation but season long application may be necessary and higher rates can cause dramatic turf injury. Other products that have met with limited success include iron, lime, chlorothalonil and soap-based products, which often fail upon repeated trials.

Leptosphaerulina australis associated with intensively managed stands of Poa annua and Agrostis palustris

Leptosphaerulina leaf blight has been sporadically documented affecting turfgrasses. Recently, a Leptosphaerulina species has been seen on diseased turfgrass samples from New England and New York State. In all cases where Leptosphaerulina has been observed in New England, it has been accompanied by a number of other turf pathogens on highly stressed hosts, so its pathogenic potential has been unclear. The purpose of this study was to identify isolates to species, determine their pathogenicity in the greenhouse, and characterize their fungicide sensitivity in vitro in the event that significant pathogenicity was demonstrated. Microscopic observation of spores and culture characteristics indicated that all examined isolates were Leptosphaerulina australis. The optimum temperature for growth was assessed and the relationship between temperature and sporulation was examined. After repeated experiments utilizing several grass species under a variety of environmental conditions, all four isolates examined were determined to be nonpathogenic. Isolates produced pseudothecia on senescent tissue but infection of live tissue was never observed. The fungicide sensitivity assay demonstrated significant variation among isolates. Based on the results of this study and other observational evidence, it is likely that this species is saprobic on senescent turfgrass leaves but not pathogenic.

Virulence of Xanthomonas translucens pv. poae Isolated from Poa annua

Bacterial wilt is a vascular wilt disease caused by Xanthomonas translucens pv. poae that infects Poa annua, a grass that is commonly found on golf course greens throughout the world. Bacterial wilt causes symptoms of etiolation, wilting, and foliar necrosis. The damage is most prevalent during the summer and the pathogen can kill turf under conditions optimal for disease development. Fifteen isolates of X. translucens pv. poae were collected from northern regions in the United States and tested for virulence against P. annua. All 15 isolates were pathogenic on P. annua, but demonstrated variable levels of virulence when inoculated onto P. annua under greenhouse conditions. The isolates were divided into two virulence groups. The first group containing four isolates generally resulted in less than 40% mortality following inoculation. The second group, containing the other eleven isolates, produced between 90 and 100% mortality following inoculation. These results suggest that differences in the virulence of bacterial populations present on a golf course may result in more or less severe amounts of observed disease.

Evaluation of Lactuca Germplasm for Resistance to the Northern Root-knot Nematode

Meloidogyne hapla Chitwood, the northern root-knot nematode, is a major pest on lettuce (Lactuca spp.) in the northeastern United States. In order to identify resistant germplasm, 494 lettuce accessions (443 L. sativa, 36 L. serriola, 7 L. virosa. and 8 L. saligna) were evaluated in the greenhouse in two trials. Six-week-old Lactuca spp. seedlings were inoculated with 5000 M. hapla eggs per plant and evaluated after 12 weeks. Galling severity and fresh root weight were measured. Of the 443 L. sativa accessions, only two, PI 508476 and PI 419140, repeatedly exhibited a root galling index of ≤2, indicating up to 20% galling, in two screening trials. Four wild Lactuca accessions, L. saligna PI 281876, L. saligna PI 491000, L. saligna 261653, and L. virosa PI 273579, were also considered highly resistant, suggesting that these accessions may be useful in hybrid breeding studies.

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.