Dr Joseph M. Vargas
Professor Botany and Plant PathologyResearch Technicians
Ron Detweiler Vargas Lab
Nancy Dykema Vargas Lab
Department of Plant Pathology 517.353.9082
Professor Botany and Plant PathologyResearch Technicians
Ron Detweiler Vargas Lab
Nancy Dykema Vargas Lab
Department of Plant Pathology 517.353.9082
2012 Report for MTF
J. M. Vargas Jr.
Professor
Co-authors: Nancy Dykema, Paul Giordano, Ron Detweiler
Dept PSM
MSU
Discovery, Identification, and Classification of a New Bacterial Pathogen of Golf Courses
P.R. Giordano and J. M. Vargas Jr.
An emerging bacterial disease caused by Acidovorax avenae subsp. avenae (Aaa) is plaguing creeping bentgrass putting greens on golf courses around the country. The pathogen was identified by the MSU turfgrass diagnostic lab in 2009, and has been isolated out of over 40 additional samples from around the U.S. since. Inoculation with suspensions of the bacterium grown in liquid broth media has shown a high degree of virulence on creeping bentgrass. Studies elucidating optimal temperature ranges for infection have shown the disease to be most severe between 30-35⁰ C in a growth chamber environment under high relative humidity. Creeping bentgrass cultivars were tested in order to determine the specificity of infection of Aaa on the particular turfgrass species. All of the cultivars inoculated Aaa were susceptible to infection when compared to control plants inoculated with sterile water. Field and growth chamber studies on creeping bentgrass were conducted to test potential chemical control options. Oxytetracycline (Mycoshield) pre-treated onto creeping bentgrass at a rate of 200 ppm was shown to significantly reduce the amount of leaf necrosis and thinning after inoculation with Aaa in a growth chamber setting when compared to an untreated, inoculated control (P < 0.0001). Thus far, this antibiotic has been the only chemical treatment to show any significant control of Aaa on creeping bentgrass in a controlled environment. Much of this initial work has been published in trade journals such as GCM and Golfdom, and more recently, the journal Plant Disease, through collaborative efforts with researchers at the University of Rhode Island.
Field work has been conducted at the MSU HTRC for the past two seasons, as well as at Moraine Country Club in 2012 to investigate in situ treatments for disease control. Etiolation was observed on inoculated field plots at the MSU site during extended periods of high heat this past summer; however, no treatments were able to significantly suppress the symptoms across the study. Similarly, control of the disease at the Moraine C.C. site was unsuccessful with any of the 14 chemical treatments evaluated. Research thus far lead to indications that the growth regulator trinexapac-ethyl (Primo Maxx) and ammonium sulfate fertilizers may play a role in exacerbating the etiolation symptom on putting greens. More work must be done on these interactions in order to fully understand the impact of these products on bacterial infection. Current work involves genetically characterizing the pathogen to closely related plant pathogenic Acidovorax spp. via multi-locus sequence typing (MLST), as well as sequencing the genome of the pathogen, which will aide in the development of a rapid PCR-based diagnostic assay.
P.R. Giordano and J. M. Vargas Jr.
An emerging bacterial disease caused by Acidovorax avenae subsp. avenae (Aaa) is plaguing creeping bentgrass putting greens on golf courses around the country. The pathogen was identified by the MSU turfgrass diagnostic lab in 2009, and has been isolated out of over 40 additional samples from around the U.S. since. Inoculation with suspensions of the bacterium grown in liquid broth media has shown a high degree of virulence on creeping bentgrass. Studies elucidating optimal temperature ranges for infection have shown the disease to be most severe between 30-35⁰ C in a growth chamber environment under high relative humidity. Creeping bentgrass cultivars were tested in order to determine the specificity of infection of Aaa on the particular turfgrass species. All of the cultivars inoculated Aaa were susceptible to infection when compared to control plants inoculated with sterile water. Field and growth chamber studies on creeping bentgrass were conducted to test potential chemical control options. Oxytetracycline (Mycoshield) pre-treated onto creeping bentgrass at a rate of 200 ppm was shown to significantly reduce the amount of leaf necrosis and thinning after inoculation with Aaa in a growth chamber setting when compared to an untreated, inoculated control (P < 0.0001). Thus far, this antibiotic has been the only chemical treatment to show any significant control of Aaa on creeping bentgrass in a controlled environment. Much of this initial work has been published in trade journals such as GCM and Golfdom, and more recently, the journal Plant Disease, through collaborative efforts with researchers at the University of Rhode Island.
Field work has been conducted at the MSU HTRC for the past two seasons, as well as at Moraine Country Club in 2012 to investigate in situ treatments for disease control. Etiolation was observed on inoculated field plots at the MSU site during extended periods of high heat this past summer; however, no treatments were able to significantly suppress the symptoms across the study. Similarly, control of the disease at the Moraine C.C. site was unsuccessful with any of the 14 chemical treatments evaluated. Research thus far lead to indications that the growth regulator trinexapac-ethyl (Primo Maxx) and ammonium sulfate fertilizers may play a role in exacerbating the etiolation symptom on putting greens. More work must be done on these interactions in order to fully understand the impact of these products on bacterial infection. Current work involves genetically characterizing the pathogen to closely related plant pathogenic Acidovorax spp. via multi-locus sequence typing (MLST), as well as sequencing the genome of the pathogen, which will aide in the development of a rapid PCR-based diagnostic assay.
Acidovorax bacteria streaming out of xylem vessels of an infected creeping bentgrass plant.
Electron micrograph of a xylem vessel plugged with Acidovorax bacteria.
Comparing the effect of three irrigation regimes and creeping bentgrass cultivars on dollar spot incidence
Nancy Dykema, Joseph Vargas, Jr., William Kirk, and Kevin Frank
One of the most economically important diseases of golf course turf is dollar spot, caused by Sclerotinia homoeocarpa. Integrated management practices and alternatives to fungicides are being investigated to combat turfgrass diseases, including dollar spot. This study compares three different irrigation regimes, based on frequency and timing, while integrating the use of resistant cultivars to assess disease management. Irrigation regimes being investigated include: light (approximately 0.25 cm) daily at 5:00 am, light (approximately 0.25 cm) daily at 10:00 pm, or infrequent (1-2 times weekly to equal the total amount of irrigation applied to the daily treatments) at 10:00 pm. Within each irrigation plot, three creeping bentgrass cultivars were randomized in four replicate split-plots. Preliminary results from one year of field testing indicate that light irrigation applied at 10:00 pm on a daily basis resulted in lower relative area under disease progress curve (AUDPC) for dollar spot in three creeping bentgrass cultivars than the same approximate total weekly volume of irrigation applied on an infrequent basis (1-2 times weekly) at 10 pm at night.
Nancy Dykema, Joseph Vargas, Jr., William Kirk, and Kevin Frank
One of the most economically important diseases of golf course turf is dollar spot, caused by Sclerotinia homoeocarpa. Integrated management practices and alternatives to fungicides are being investigated to combat turfgrass diseases, including dollar spot. This study compares three different irrigation regimes, based on frequency and timing, while integrating the use of resistant cultivars to assess disease management. Irrigation regimes being investigated include: light (approximately 0.25 cm) daily at 5:00 am, light (approximately 0.25 cm) daily at 10:00 pm, or infrequent (1-2 times weekly to equal the total amount of irrigation applied to the daily treatments) at 10:00 pm. Within each irrigation plot, three creeping bentgrass cultivars were randomized in four replicate split-plots. Preliminary results from one year of field testing indicate that light irrigation applied at 10:00 pm on a daily basis resulted in lower relative area under disease progress curve (AUDPC) for dollar spot in three creeping bentgrass cultivars than the same approximate total weekly volume of irrigation applied on an infrequent basis (1-2 times weekly) at 10 pm at night.
Overview of dollar spot irrigation study