Progress 10/01/03 to 09/30/09

Outputs
OUTPUTS: During the course of this project several field experiments were conducted that served as sources of information that were presented at the University of Georgia Turfgrass Field Day and the Georgia Turfgrass Institute and Trade Show. In addition results of the experiments were used to update the turfgrass section of the undergraduate course Turfgrass Pest Management (CSS/ENT/PATH 3500) at the University of Georgia. A website associated with the pathology section of the course (http://lburpee.myweb.uga.edu/index.html) was updated annually with new information gleaned from the field experiments. PARTICIPANTS: L.L. Burpee, Professor of Plant Pathology, University of Georgia served as principle investigator for the project. Samuel Stephens, Research Professional I, University of Georgia provided technical assistance. Training and development opportunities were provided to Shannon Nix, Post-Doctoral Associate, University of Georgia. Dr. Nix played a key role in the research conducted on the ecology of phylloplane yeast. TARGET AUDIENCES: Target groups included members of the turfgrass industry (lawn care personnel, sports field managers, golf course superintendents, agricultural chemical companies) in Georgia and thougout the U.S. In addition, research groups involved in phylloplane ecology and turfgrass disease management were targets of our research efforts. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Significant outcomes/impacts from this project included information on a novel way to control anthracnose disease of turfgrass with phosphonate fungicides, identification of selections of seashore paspalum that exhibit resistance to Sclerotinia homoeocarpa, the cause of dollar spot disease, and evidence of how phylloplane yeast respond to wounding and fungal infection of turfgrass leaves.

Publications

• Burpee, L.L. and Latin, R.X. 2008. Reassessment of fungicide synergism for control of dollar spot. Plant Dis. 92: 601-606.
• Nix, S.S., Burpee, L.L., Jackson, K.L. and Buck, J.W. 2008. Short-term temporal dynamics of yeast abundance on the tall fescue phylloplane. Can. J. Microbiol. 54: 299-304.

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: Populations of naturally-occurring yeasts are reported to play a role in the suppression of diseases on plant leaves, flowers and fruit. In previous studies, we found that yeasts are abundant on the leaf surface (phylloplane) of turfgrasses. Therefore, experiments were conducted to assess the effects of short-term temporal dynamics and foliar applications of nutrients on the phylloplane yeast community of tall fescue. Results of this study were reported at the annual meeting of the American Phytopathological Society for 2007. PARTICIPANTS: Post-doctoral associate, Shannon Nix, conducted experiments, analyzed data and wrote the initial drafts of papers. L.L. Burpee, Professor of Plant Pathology, secured the funding for the project through unrestricted gifts provided to the University of Georgia by chemical companies. These gifts were provided to support turfgrass research at the university. In addition, L.L. Burpee provided expertise on turfgrass biology and management to the project. J.W. Buck, Associate Professor of Plant Pathology, provided expertise on yeast biology and physiology to the project. The project served as post-doctoral training and development in microbiology and plant pathology for Shannon Nix. TARGET AUDIENCES: Target audiences include groups interested in control and management of turfgrass diseases, e.g. turfgrass managers, sod producers, chemical companies. Information on this project was made available to these groups during the University of Geogia Turfgrass Field Day 2007.

Impacts
A solution consisting of 2% sucrose + 0.5% yeast extract or sterile de-ionized water (control) was applied at 0600 hrs to tall fescue field plots maintained at the University of Georgia Griffin Campus near Griffin, GA. Leaf samples were collected 12 hr after treatment, and yeast colony forming units (cfu) were detected by dilution plating. This process was repeated again at 1200, 1800 and 0000 (midnight) hours in each of six replicate trials. Significant differences were observed between the number of yeast cfu and the time at which the samples were collected. On average, the number of yeast cfu recovered was significantly less at 1800 hours and significantly greatest at 0000 hours when compared to all other sampling times. In addition, a significant trend of increased yeast abundance was detected on tall fescue foliage treated with the nutrient solution compared to control treatments. In a separate investigation, atmospheric yeast abundance above the canopy of tall fescue was assessed in the morning (0900 hours) and in the afternoon (1500) using a Thermo Andersen single stage viable particle sampler. In 5 of the 6 trials of this experiment, atmospheric yeast abundance was significantly greater in the morning than in the afternoon. The results of our atmospheric and leaf washing experiments suggest that phylloplane yeast populations on tall fescue increase during the late evening and early morning, stabilize during the late morning and early afternoon through exchange of immigrants and emigrants and decline during the late afternoon/early evening.

Publications

• Nix-Stohr, S., Burpee, L.L. and Buck J.W. 2007. The influence of exogenous nutrients on the abundance of yeasts on the phylloplane of turfgrass. Micobial Ecol. DOI: 10.1007/s00248-0079246-x.
• Nix, S.S., Burpee, L.L. and Buck, J.W. 2007. The effects of wounding and fungal infection on two phylloplane yeast populations in tall fescue. Phytopathology 97: S85.
• Nix-Stohr, S., Burpee, L.L. and Buck, J.W. 2007. The influence of exogenous nutrients on the abundance of yeasts on the phylloplane of tall fescue. Phytopathology 97: S182.

Progress 01/01/06 to 12/31/06

Outputs
Experiments were conducted to assess the effect of foliar applications of various nutrient solutions on the phylloplane yeast community of tall fescue (Festuca arundinacea Schreb.). In the first three experiments increasing concentrations of sucrose (2-16%), yeast extract (0.5-2.5%) and sucrose plus yeast extract (2.5-18.5% total) were applied and the yeast colony forming units (cfu) enumerated 10 hours later by dilution plating. Significant positive linear relationships were observed between the number of yeast cfu and applications of yeast extract or sucrose plus yeast extract. Foliar applications of sucrose alone had no significant effect on yeast community abundance, indicating that phylloplane yeasts of turfgrass are not limited by the amount or availability of carbohydrates. In a subsequent experiment, five different solutions were applied to tall fescue to investigate the response of the yeast community to organic and inorganic nitrogen sources. Tryptone or yeast extract, both with considerable amino acid composition, significantly increased the yeast population while yeast nitrogen base (with or without amino acids) and ammonium sulfate had no affect on yeast abundance. These results suggest that organic nitrogen stimulates yeast community growth and development on the phylloplane of tall fescue while carbohydrates, inorganic nitrogen and non-nitrogenous nutrients have little positive effect.

Impacts
Results indicate that yeast populations on leaves of tall fescue plants can be increased by applying organic sources of nitrogen. This may play a role in biological control of foliar pathogens by yeast species.

Publications

• Allen, T.W., Burpee, L.L. and Buck, J.W. 2006. Variable adhesion and diurnal population patterns of epiphytic yeasts on creeping bentgrass. Can. J. Microbiol. 52: 404-410.

Progress 01/01/05 to 12/31/05

Outputs
Anthracnose, caused by Colletotrichum graminicola, is a serious disease of creeping bentgrass (Agrostis stolonifera L.) and annual bluegrass (Poa annua L.) in the United States and Europe. Applications of phosphonate fungicides have provided variable control of anthracnose in field trials. The objective of this study was to relate this variability to possible differences in sensitivity of C. graminicola isolates to potassium phosphonate (PP) and fosetyl aluminum (FA). Sensitivity of isolate CG00-06 was assessed by measuring colony diameter on potato-dextrose agar (PDA) amended with PP (Alude 5.7L, Cleary Chemical Corp., Dayton, NJ) or FA (Aliette 80WP or Chipco Signature 80WP, Bayer Crop Science, Kansas City, MO). Six concentrations of PP ranging from 30 to 170 ug a.i./ml and six concentrations of each formulation of FA ranging from 160 to 780 ug a.i./ml were prepared. Significant linear relationships were detected between percent growth inhibition of CG00-06 and concentration of each fungicide tested. Concentrations providing 50 percent inhibition (EC50) for PP and FA (Aliette 80WP) were 121.9 and 364.6 ug/ml, respectively. A higher EC50 (401.7 ug/ml) was detected for the Chipco Signature formulation of FA. Phosphonate sensitivities of eleven additional isolates of C. graminicola were compared on PDA amended with PP and FA (Aliette 80WP) at 125 and 400 ug/ml. Significant differences in relative growth occurred among isolates exposed to each fungicide. Relative growth of isolate CG00-06 was less than that of other C. graminicola isolates on media amended with PP and FA. When compared to single isolates of Rhizoctonia solani, Sclerotinia homoeocarpa, Gaeumannomyces graminis var. graminis, and Pyricularia grisea, isolates of Pythium aphanidermatum and C. graminicola were the only fungi tested that exhibited significant reductions in relative growth when exposed to PP and FA at 0.64, 1.45, and 3.14 P03 meq/L.

Impacts
Results indicate that isolates of Colletotrichum gramincola are sensitive to phosphonate fungicides. These fungicides can be used to control anthracnose caused by strains of C. graminicola that are resistant to benzimidazole and demethylation inhibitor fungicides.

Publications

• Allen, T.W., Burpee, L.L., and Buck, J.W. 2004. In vitro attachment of phylloplane yeasts to Botrytis cinerea, Rhizoctonia solani, and Sclerotinia homoeocarpa. Can. J. Microbiol. 50:1041-1048.
• Allen, T.W., Martinez, A., and Burpee, L.L. 2005. Dollar spot of turfgrass. The Plant Health Instructor. DOI 10.1094/PHI-I-2005-0217-02.
• Burpee, L.L. 2005. Sensitivity of Colletotrichum graminicola to phosphonate fungicides. J. Int. Turf Res. Soc. 10: 163-169.
• Tredway, L.P., K.L. Stevenson, and L.L. Burpee. 2005. Genetic structure of Magnaporthe grisea populations associated with St. Augustinegrass and tall fescue in Georgia. Phytopathology 95: 463-471.
• Martinez A., Burpee L., and Waltz C. 2005. Abiotic Injuries and disorders of Turfgrasses in Georgia in Spanish. CES-CAES-UGA Bulletin B1258-SP. Martinez A., Burpee L., and Waltz C. 2005. Abiotic Injuries and disorders of Turfgrasses in Georgia. CES-CAES-UGA Bulletin B1258.

Progress 01/01/04 to 12/31/04

Outputs
The effects of fungicides on population size and development of fungicide resistance in the phylloplane yeast flora of creeping bentgrass (Agrositis palustris) was investigated. Azoxystrobin, chlorothalonil, flutolanil, and propiconazole were applied separately over a 6-week period to field plots of creeping bentgrass. Total and fungicide-resistant yeast populations were assessed by dilution plating onto either potato dextrose agar (PDA) or PDA amended with the test fungicides. Total yeast populations in the fungicide-treated plots were significantly lower than populations in check plots on three out of four sampling dates. In another test, azoxystrobin or propiconazole were applied twice to plots of bentgrass over 3 weeks. Significantly larger total yeast populations were detected compared to resistant and highly resistant populations for each treatment on each sample date. Total yeast populations were significantly higher in check plots compared with populations from either propiconazole- or azoxystrobin-treated plots on the first three of five sample dates. A collection of yeasts (N=114) with no prior exposure to fungicides was more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N=115) isolated from fungicide treated turfgrass.

Impacts
The results suggest that fungicide resistance among phylloplane yeasts is widespread and can be an important factor in the development of biological control agents for turfgrass disease.

Publications

• Allen, T.W., Quayyum, H.A., Burpee, L.L. and Buck, J.W. 2004. Effect of foliar disease on the epiphytic yeast communities of creeping bentgrass and tall fescue. Can J. Microbiol. 50: 853-860.
• Allen, T.W., Burpee, L.L., and Buck, J.W. 2004. Effect of foliar disease on epiphytic yeast populations of creeping bentgrass and tall fescue. Phytopathology 94: S3.
• Allen, T.W., Burpee, L.L., and Buck, J.W. 2004. Effect of overhead irrigation on phylloplane yeast populations on bentgrass and tall fescue. Phytopathology 94: S4.
• Pearce, M., Martinez-Espinoza, A.D., and Burpee, L.L. 2004. Diagnosis, characterization, and dynamics of turfgrass diseases in the commercial and homeowner setting in Georgia in 2002. Phytopathology 94: S146.
• Pearce, M.J., Martinez-Espinoza, A.D., and Burpee, L.L. 2004. Turfgrass disease characterizations in the state of Georgia before and after commercial disease management field trainings in 2002 and 2003. Phytopathology 94: S82.