scholarly journals Factors affecting pathogenicity of the turfgrass dollar spot pathogen in natural and model hosts

2019 ◽  
Author(s):  
R.A. Rioux ◽  
C.M. Stephens ◽  
J.P. Kerns
Keyword(s):  
Oxalic Acid ◽  
Time Course ◽  
Creeping Bentgrass ◽  
Initial Contact ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Factors Affecting ◽  
Whole Plant ◽  
Host Infection

AbstractClarireediasp. (formerly calledSclerotinia homoeocarpa), the fungal pathogen that causes dollar spot of turfgrasses, produces oxalic acid but the role of this toxin inClarireediasp. pathogenesis is unknown. In the current study, whole plant inoculation assays were used to evaluate pathogenesis ofClarireediasp. in various model hosts and investigate the role of oxalic acid in dollar spot disease. These assays revealed that both host endogenous oxalate content and pathogen-produced oxalic acid influence the timing and magnitude of symptom development. In time-course expression analysis, oxalate oxidase and related defense-associated germin-like protein genes in creeping bentgrass showed strong up-regulation starting at 48-72 hpi, indicating that germin-like protein genes are most likely involved in defense following initial contact with the pathogen and demonstrating the importance of oxalic acid inClarireediasp. pathogenesis. Overall, the results of these studies suggest that oxalic acid and host endogenous oxalate content are important for pathogenesis byClarireediasp. and may be associated with the transition from biotrophy to necrotrophy during host infection.

scholarly journals Role of mechanical cues and hypoxia on the growth of tumor cells in strong and weak confinement: A dual in vitro–in silico approach

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz7130 ◽  
Author(s):  
V. Le Maout ◽  
K. Alessandri ◽  
B. Gurchenkov ◽  
H. Bertin ◽  
P. Nassoy ◽  
...  
Keyword(s):  
In Silico ◽  
Time Course ◽  
Growth Dynamics ◽  
Tumor Model ◽  
Mechanistic Modeling ◽  
Physical Factors ◽  
Factors Affecting ◽  
Numerical Studies

Characterization of tumor growth dynamics is of major importance for cancer understanding. By contrast with phenomenological approaches, mechanistic modeling can facilitate disclosing underlying tumor mechanisms and lead to identification of physical factors affecting proliferation and invasive behavior. Current mathematical models are often formulated at the tissue or organ scale with the scope of a direct clinical usefulness. Consequently, these approaches remain empirical and do not allow gaining insight into the tumor properties at the scale of small cell aggregates. Here, experimental and numerical studies of the dynamics of tumor aggregates are performed to propose a physics-based mathematical model as a general framework to investigate tumor microenvironment. The quantitative data extracted from the cellular capsule technology microfluidic experiments allow a thorough quantitative comparison with in silico experiments. This dual approach demonstrates the relative impact of oxygen and external mechanical forces during the time course of tumor model progression.

scholarly journals Residual Efficacy of Fungicides for Control of Dollar Spot on Creeping Bentgrass

Plant Disease ◽  
2006 ◽  
Vol 90 (5) ◽  
pp. 571-575 ◽  
Author(s):  
Richard Latin
Keyword(s):  
Creeping Bentgrass ◽  
Effective Concentration ◽  
Disease Suppression ◽  
Golf Course ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Residual Efficacy ◽  
Bioassay Technique ◽  
Precipitous Decline ◽  
Field Plots

The duration of effective concentrations of fungicides for control of dollar spot on creeping bentgrass fairways was investigated using a bioassay technique. In each of three runs of the experiment, fungicide treatments were applied once to turf in replicated field plots; then, the plots were sampled periodically over 3 weeks by removing turf plugs from the field. The sampled plugs were placed in incubation containers and inoculated with sections from a 4-day-old colony of Sclerotinia homoeocarpa growing on potato dextrose agar. After a 96-h incubation period, the extent of pathogen growth on the turf plugs was measured. Results described a precipitous decline in effective concentration for all fungicide treatments beginning 7 to 10 days after application. The fungicides were only marginally effective at 14 days after application, and none provided any disease suppression at 21 days after application. The efficacy half-life (EHL) associated with four of the fungicides (chlorothalonil, iprodione, propiconazole, and thiophanate methyl) was estimated with two models. EHL estimates ranged from 6.1 to 15.2 days depending on the fungicide and the model. This research contributes to our knowledge of the duration of effective fungicide concentrations on creeping bentgrass and can provide insight for scheduling fungicide sprays for golf course fairways.

scholarly journals Genetic Diversity of Sclerotinia homoeocarpa Isolates from Turfgrasses from Various Regions in North America

Plant Disease ◽  
2004 ◽  
Vol 88 (11) ◽  
pp. 1269-1276 ◽  
Author(s):  
G. Viji ◽  
W. Uddin ◽  
N. R. O'Neill ◽  
S. Mischke ◽  
J. A. Saunders
Keyword(s):  
United States ◽  
Genetic Diversity ◽  
Creeping Bentgrass ◽  
The United States ◽  
Vegetative Compatibility ◽  
Major Group ◽  
Golf Courses ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Geographical Regions

Sixty-seven isolates of Sclerotinia homoeocarpa, causing dollar spot disease in creeping bentgrass, annual bluegrass, Bermudagrass, and perennial ryegrass turf, collected from 23 golf courses in various geographical regions of the United States and Canada between 1972 and 2001, were characterized by vegetative compatibility, genetic diversity, and pathogenicity. Eleven vegetative compatibility groups (VCGs A to K) were identified among the isolates tested in this study, and five of them (VCGs G to K) were new. VCG B was the most predominant group, typifying 33 isolates (51%) tested. S. homoeocarpa isolates collected from golf courses in Pennsylvania belonged to seven VCGs (A, B, E, F, G, I, and K), whereas three groups were observed in those collected from New York (B, E, and G) and New Jersey (E, H, and I). Two isolates, one each from Pennsylvania and Canada, were incompatible when paired with the tester isolates in all possible combinations, and did not fall into any known VCG. An isolate collected from Canada was compatible with tester isolates from two VCGs (C and D). Genetic analyses using amplified fragment length polymorphism (AFLP) showed the presence of two genetically distinct groups, designated as major group and the minor group. The major group included 36 isolates collected from various golf courses in the United States and Canada. Two isolates collected from bermudagrass in Florida formed a separate cluster, the minor group. Isolates that belonged to the major group were further divided into two subgroups (1 and 2). Subgroup 1 consisted of all the isolates that belonged to VCGs A, E, G, H, and I. Three of the four isolates that belonged to VCG K also were clustered with isolates of subgroup 1. Subgroup 2 consisted of all the isolates from VCG B, and one each from VCGs F and K. Pathogenicity assays on Penncross creeping bentgrass showed significant differences (P = 0.05) in virulence among the isolates. Overall, a relationship between virulence and VCGs was observed, in which certain virulence groups corresponded to specific VCGs; however, such a relationship was not observed between virulence and AFLPs. Close similarity among isolates of S. homoeocarpa collected from different locations in the United States and Canada suggests that isolates of the same genotype could be involved in outbreaks of dollar spot epidemics at multiple locations.

scholarly journals Mowing Frequency and Plant Growth Regulator Effects on Dollar Spot Severity and on Duration of Dollar Spot Control by Fungicides

Plant Disease ◽  
2011 ◽  
Vol 95 (11) ◽  
pp. 1433-1442 ◽  
Author(s):  
Alexander I. Putman ◽  
John E. Kaminski
Keyword(s):  
Plant Growth ◽  
Creeping Bentgrass ◽  
Agrostis Stolonifera ◽  
Golf Course ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Confounding Effect ◽  
Residual Efficacy ◽  
The University ◽  
University Of Connecticut

Management of dollar spot (incited by Sclerotinia homoeocarpa) on golf course fairways is increasingly challenging. The objectives of this study were to determine the influence of mowing frequency and plant growth regulators (PGRs) on dollar spot severity and on the residual efficacy of fungicides for control of dollar spot. Two 4-month-long studies were conducted on ‘Putter’ creeping bentgrass (Agrostis stolonifera) maintained as a fairway at the University of Connecticut. Treatments were arranged in a three-by-three-by-five factorial that assessed the influence of mowing frequency (2, 4, or 6 days week–1) and PGRs (paclobutrazol, trinexapac-ethyl, or none) on dollar spot control by five fungicide treatments (boscalid, chlorothalonil, iprodione, propiconazole, or none). Turf was mowed in the afternoon hours to minimize the confounding effect of mowing frequency on leaf wetness duration. Treatments were initiated in the late spring of 2007 and 2008, and each fungicide treatment was reapplied only when dollar spot exceeded a threshold of five infection centers plot–1. In the absence of fungicides, dollar spot severity was reduced by 63 to 90% in plots treated with paclobutrazol and by 13 to 55% in plots treated with trinexapac-ethyl. Dollar spot severity was 23 to 50% lower in plots mown 2 days week–1 compared with those mown 6 days week–1. In cases where a significant interaction was observed between mowing frequency and PGRs, dollar spot was reduced on most rating dates in plots treated with trinexapacethyl that were mown 2 days week–1 compared with those mown 6 days week–1. Survival analysis of days until threshold was met revealed that duration of control of fungicides in plots receiving paclobutrazol were 28 to 84% longer compared with plots not receiving PGR. Duration of control by fungicides was generally similar between plots treated with trinexapac-ethyl and no PGR. In general, mowing frequency did not influence duration of control. Results from this study indicate that paclobutrazol could be used to increase the treatment interval of fungicides and that mowing frequency in the absence of dew is likely to have little influence on fungicide residual efficacy. When used without fungicides, PGRs and less frequent mowing may reduce dollar spot in situations where fungicide use is limited.

RELATIONSHIP BETWEEN WEATHER FACTORS AND DOLLAR SPOT OF CREEPING BENTGRASS

1984 ◽  
Vol 64 (1) ◽  
pp. 167-174 ◽  
Author(s):  
ROBERT HALL
Keyword(s):  
Disease Control ◽  
Creeping Bentgrass ◽  
Weather Conditions ◽  
Acceptable Level ◽  
Sclerotinia Homoeocarpa ◽  
Agrostis Palustris ◽  
Dollar Spot ◽  
Weather Factors ◽  
Average Temperature

In 1981 and 1982 epidemics of dollar spot of creeping bentgrass, caused by Sclerotinia homoeocarpa, proceeded in a series of steps. Each step began at a point where a decline in the epidemic rate was followed by an increase in the epidemic rate and continued until a new step began. A step in the epidemic occurred after two consecutive wet days if the average temperature for the period was at or above 22 °C or after three or more consecutive wet days if the average temperature for the period was 15 °C or greater. These weather conditions were referred to as "infection periods." In 1982, an application of Tersan 1991 (benomyl) 1 and 2 days after two infection periods provided an acceptable level of disease control as effective as that obtained from a regular preventive schedule of seven sprays.Key words: Agrostis palustris, disease control, Sclerotinia homoeocarpa, weather-timed spray

scholarly journals Seasonal Development of Dollar Spot Epidemics in Six Creeping Bentgrass Cultivars in Maryland

HortScience ◽  
2012 ◽  
Vol 47 (3) ◽  
pp. 422-426 ◽  
Author(s):  
Christopher P. Ryan ◽  
Peter H. Dernoeden ◽  
Arvydas P. Grybauskas
Keyword(s):  
Creeping Bentgrass ◽  
Seasonal Development ◽  
Golf Courses ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Severe Damage ◽  
Start Date ◽  
Degree Day ◽  
Progress Curve ◽  
The Many

This 3-year field study evaluated the incidence and severity of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in six creeping bentgrass (Agrostis stolonifera L.) cultivars maintained as a golf course fairway. Comparison of area under the disease progress curve (AUDPC) data clearly indicted two resistance groups among the six cultivars. ‘Crenshaw’ and ‘Backspin’ were classified as highly susceptible (HS) and the other four cultivars (i.e., ‘Penncross’, ‘Providence’, ‘L-93’, and ‘007’) were classified as moderately susceptible (MS) to dollar spot. In all three study years, there were three epidemics that began in May. Data could not be collected in HS cultivars after the first epidemic in each year as a result of severe damage. In MS cultivars, the first epidemic ended and a second began between early July and late August. The second epidemic ended approximately mid-October and a third epidemic appeared in MS cultivars between late October and early December. The second epidemic was longest and most severe, and the third fall epidemic was least severe and of shortest duration. The first epidemic in HS cultivars developed up to two weeks earlier and progressed more rapidly and severely than in MS cultivars. A growing degree-day (GDD) model, using a base air temperature of 15 °C and a start date of 1 Apr., was accurate in predicting the onset of the first epidemic in HS (60 to 70 GDD) and MS (105 to 115 GDD) cultivars during each of the three study years. Growing degree-day models are greatly influenced by the many microclimates found on golf courses and need to be evaluated for accuracy in diverse environments.

scholarly journals Regulation with Trinexapac-ethyl and Dew Removal at the Time of Fungicide Application Did Not Influence Dollar Spot Control

HortScience ◽  
2015 ◽  
Vol 50 (3) ◽  
pp. 496-500
Author(s):  
Yu Huang ◽  
John E. Kaminski ◽  
Peter J. Landschoot
Keyword(s):  
Management Practice ◽  
Creeping Bentgrass ◽  
Golf Courses ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Fungicide Application ◽  
Previously Treated ◽  
Northern United States ◽  
Reduce Disease Severity ◽  
Important Disease

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is an important disease of creeping bentgrass (Agrostis stolonifera L.) on golf courses in the northern United States. Canopy moisture in the form of dew plays an important role in the development of dollar spot and routine displacement has been shown to reduce disease severity. The use of plant growth regulators (PGRs) is a common management practice for maintaining creeping bentgrass fairways, but their influence on dollar spot is unclear. The objective of this field study was to elucidate the influence of dew removal at the time of fungicide application on dollar spot control in creeping bentgrass regulated by trinexapac-ethyl (TE). Main factors in the study included three dew removal strategies (non-treated, dew removed–mowed, and dew removed–not mowed) before the application of four fungicide treatments (non-treated, chlorothalonil, propiconazole, and iprodione). All fungicide treatments were applied once to turfgrass previously treated with TE or not treated. The presence or absence of dew at the time of fungicide application generally had no influence on fungicide performance with respect to dollar spot control. Based on the results of this study, dew removal before the application of fungicides targeting dollar spot is unnecessary. Applications of TE before fungicides reduced dollar spot severity in some cases, but reductions in symptom expression were limited and did not result in markedly improved dollar spot control.

scholarly journals Brachypodium: A Potential Model Host for Fungal Pathogens of Turfgrasses

2017 ◽  
Vol 107 (6) ◽  
pp. 749-757 ◽  
Author(s):  
Renee A. Rioux ◽  
Benjamin J. Van Ryzin ◽  
James P. Kerns
Keyword(s):  
Fungal Pathogens ◽  
Molecular Mechanisms ◽  
Brachypodium Distachyon ◽  
Creeping Bentgrass ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Cool Season ◽  
Host System ◽  
Brown Patch ◽  
Compatible Interactions

Brachypodium distachyon is a C3 grass that is an attractive model host system for studying pathogenicity of major turfgrass pathogens due to its genetic similarity to many cool-season turfgrasses. Infection assays with two or more isolates of the casual agents of dollar spot, brown patch, and Microdochium patch resulted in compatible interactions with B. distachyon inbred line Bd21-3. The symptoms produced by these pathogens on Bd21-3 closely resembled those observed on the natural turfgrass host (creeping bentgrass), demonstrating that B. distachyon is susceptible to the fungal pathogens that cause dollar spot, brown patch, and Microdochium patch on turfgrasses. The interaction between Sclerotinia homoeocarpa isolates and Brachypodium ecotypes was also investigated. Interestingly, differential responses of these ecotypes to S. homoeocarpa isolates was found, particularly when comparing B. distachyon to B. hybridum ecotypes. Taken together, these findings demonstrate that B. distachyon can be used as a model host system for these turfgrass diseases and leveraged for studies of molecular mechanisms contributing to host resistance.

scholarly journals Control of Dollar Spot of Creeping Bentgrass Caused by an Isolate of Sclerotinia homoeocarpa Resistant to Benzimidazole and Demethylation-Inhibitor Fungicides

Plant Disease ◽  
1997 ◽  
Vol 81 (11) ◽  
pp. 1259-1263 ◽  
Author(s):  
L. L. Burpee
Keyword(s):  
Incubation Period ◽  
Field Tests ◽  
Creeping Bentgrass ◽  
Disease Suppression ◽  
Sclerotinia Homoeocarpa ◽  
Dollar Spot ◽  
Fungicide Sensitivity ◽  
Thiophanate Methyl ◽  
Demethylation Inhibitor

The effects of fungicides were studied on two isolates of Sclerotinia homoeocarpa that differed in fungicide sensitivity. Concentrations of benzimidazole (benomyl and thiophanate-methyl), demethylation inhibitor (fenarimol, propiconazole, and triadimefon), and nitrile (chlorothalonil) fungicides required to inhibit mycelial growth in vitro by 50 and 90% (effective concentration; EC50,90) were significantly greater for isolate S088 than for isolate S084. No differences were observed in the EC50,90 values of a pyridylaniline (fluazinam) or dicarboximide (iprodione) fungicide. In field tests conducted on creeping bentgrass, S088 had a significantly shorter incubation period than S084 in plots treated with propiconazole applied at 0.2 or 0.8 kg a.i. ha-1 in 1994 or 0.4 kg a.i. ha-1 in 1995, thiophanate-methyl applied at 1.5 or 3.0 kg a.i. ha-1 in 1994 and 1995, or a tank-mix of propiconazole and iprodione applied at 1.6 + 0.8 kg a.i. ha-1 in 1994. No differences in incubation periods occurred in plots treated with chlorothalonil or iprodione in either year, or with fluazinam in 1995 and 1996. Fewer days were required to reach 5% disease severity in turf inoculated with isolate S088, compared to isolate S084, in plots treated with propiconazole, thiophanate-methyl, or certain tank-mixes containing propiconazole, in 1994 and 1995. Several treatments, including propiconazole, thiophanate-methyl, and fluazinam, resulted in suppression of disease caused by isolate S084 to less than 5% severity for more than 21 days, while only fluazinam applied at 1.6 or 3.2 kg a.i. ha-1 provided more than 21 days of disease suppression in turf inoculated with either of the isolates tested. Slope coefficients from linear regressions between incubation period or days to 5% disease and concentrations of fungicide applied in 1996 were significantly different for isolate S084 compared to isolate S088 in plots treated with propiconazole, but not in plots treated with fluazinam.

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