Sublethal Doses of Mefenoxam Enhance Pythium Damping-off of Geranium

Garzón, Carla D.; Molineros, Julio E.; Yánez, Jennifer M.; Flores, Francisco; Jiménez-Gasco, María del Mar; Moorman, Gary W.

doi:10.1094/pdis-09-10-0693

Cited by 48 publications

(22 citation statements)

References 51 publications

(43 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Each column in the figure represented the mean value and standard error of 24 replicates. Stimulations on mycelial growth and virulence by sublethal doses of fungicides have been observed in ascomycetes (1) and basidiomycetes (16,23) as well as in oomycetes (18). The potential effects of fungicide hormesis are highly detrimental, because they may result in greater disease incidence and severity, larger crop losses, and higher mycotoxin levels in grains (1).…”

Section: Discussionmentioning

confidence: 99%

“…de Bary to fungicide, we noticed that some isolates grew faster on potato dextrose agar (PDA) media amended with sublethal doses of fungicides than on fungicide-free PDA media. There have been some reports of plant pathogen growth and virulence stimulations by sublethal doses of fungicides or other chemicals (e.g., stimulation of Pythium damping-off of geranium by sublethal doses of mefenoxam; 18,19). The stimulations of sublethal doses of fungicides on phytopathogens probably belong to a phenomenon called hormesis.…”

mentioning

confidence: 99%

“…More concerning about sublethal doses of fungicides is their virulence stimulatory effects on plant pathogens. Garzon et al (18) reported that mycelial growth stimulatory effects of sublethal doses of mefenoxam on a mefenoxam-resistant isolate of P. aphani dermatum was about a 10% increase over the control whereas the percent stimulation on virulence of P. aphanidermatum on geranium seedlings was as high as 61%. There is a possibility that virulence stimulations maybe relate to endogenous hydrogen peroxide (H20 2) or oxalic acid in plant pathogens because these two compounds play a crucial role in fungal pathogenesis on host plants (1,4,12,15,35).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Stimulatory Effects of Sublethal Doses of Dimethachlon on Sclerotinia sclerotiorum

Zhou

Liang

et al. 2014

Plant Disease

View full text Add to dashboard Cite

A b s t r a c t -X. 2014. Stimulatory effects of sublethal doses of dimethachlon on Sclerotinia sclerotiorum. Plant Dis. 98:1364-1370.Growth and virulence stimulations of sublethal doses of fungicides on plant-pathogenic fungi and oomycetes have been reported and the stimulatory effects are potentially relevant to plant disease manage ment. Sclerotinia sclerotiorum is one of the most devastating and eco nomically important necrotrophic fungal phytopathogens, capable of infecting more than 400 species of plants worldwide. In order to study stimulatory effects of sublethal doses of fungicides on S. sclerotiorum, 55 dimethachlon-sensitive isolates and 3 dimethachlon-resistant iso lates of S. sclerotiorum were assayed to determine effects of sublethal doses of dimethachlon on mycelial growth rate on potato dextrose agar (PDA) media and virulence on oilseed rape plants. Results showed that all 3 dimethachlon-resistant isolates and 13 of the 55 sensitive isolates exhibited stimulatory responses to sublethal doses of dimethachlon.Dimethachlon-resistant isolates grew significantly (P < 0.05) faster on PDA media amended with dimethachlon at 0.5 to 4 pg/ml than on fungicide-free PDA media. As for virulence on detached leaves of oilseed rape plants, lesion diameters of dimethachlon-resistant isolates after growth on PDA media amended with dimethachlon at 0.5 to 2 pg/ml were significantly larger (P < 0.05) than the control. The maxi mum stimulatory effects were 42.40 to 59.80%. In pot experiments, for both dimethachlon-sensitive and -resistant isolates, significant (P < 0.05) virulence stimulations were observed after spraying with di methachlon at a concentration of 2 pg/ml. After growing on dimethachlon-amended PDA media, H20 2 sensitivity of S. sclerotiorum de creased significantly (P < 0.05) compared with the nonamended PDA control.At present, fungicides still play an essential and, in most cases, maybe the most important role in successful and effective plant disease management. When controlling fungal and oomycete plant pathogens by application of fungicides, a small amount of phyto pathogens will inevitably be exposed to sublethal doses of fungi cides. Exposure to sublethal doses of fungicides can occur under diverse circumstances, such as inappropriate fungicide applica tions, in combination with other fungicides with different active ingredient, and emergence of fungicide-resistant strains (16,26). Normal doses of fungicides for sensitive phytopathogen strains are perhaps sublethal doses for fungicide-resistant strains. In most experiments, researchers are mainly interested in effects of normal (high) doses of fungicides on plant pathogens, and effects of suble thal doses of fungicides have been largely ignored.In experiments to test in vitro sensitivity of Sclerotinia scleroti orum (Lib.) de Bary to fungicide, we noticed that some isolates grew faster on potato dextrose agar (PDA) media amended with sublethal doses of fungicides than on fungicide-free PDA media. There have been some reports of plant pathogen growth...

show abstract

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Stimulatory Effects of Sublethal Doses of Dimethachlon on Sclerotinia sclerotiorum

Zhou

Liang

et al. 2014

Plant Disease

View full text Add to dashboard Cite

show abstract

“…Fungicide sensitivity of field isolates can be measured by calculating 50% effective concentration (EC50) values (14,25,26,30,(37)(38)(39)43). The EC50 value is the concentration of fungicide in media that reduces fungal growth or spore germination by 50% compared with growth on nonamended media (38).…”

mentioning

confidence: 99%

“…In some locations, growers may apply reduced fungicide rates in attempts to decrease inputs and increase profits. However, reduced rates may give a sublethal dose to a portion of a field population, which may increase the frequency of mutations in a location and accelerate the evolution of fungicide resistance (15) or cause increased disease severity (14). As part of our ongoing research on fungicide resistance management in this pathosystem, we are interested in the relationship between reduced sensitivity to fungicides as measured by EC50 values and the loss of disease control at field, or lower, fungicide rates to provide greater translational meaning of EC50 values.…”

mentioning

confidence: 99%

Efficacy of Variable Tetraconazole Rates Against Cercospora beticola Isolates with Differing In Vitro Sensitivities to DMI Fungicides

et al. 2012

View full text Add to dashboard Cite

Bolton, M. D., Rivera-Varas, V., del Rio Mendoza, L. E., Khan, M. F. R., and Secor, G. A. 2012. Efficacy of variable tetraconazole rates against Cercospora beticola isolates with differing in vitro sensitivities to DMI fungicides. Plant Dis. 96:1749-1756.Cercospora leaf spot (CLS) of sugar beet is caused by the fungus Cercospora beticola. CLS management practices include the application of the sterol demethylation inhibitor (DMI) fungicides tetraconazole, difenoconazole, and prothioconazole. Evaluating resistance to DMIs is a major focus for CLS fungicide resistance management. Isolates were collected in 1997 and 1998 (baseline sensitivity to tetraconazole, prothioconazole, or difenoconazole) and 2007 through 2010 from the major sugar-beet-growing regions of Minnesota and North Dakota and assessed for in vitro sensitivity to two or three DMI fungicides. Most (47%) isolates collected in 1997-98 exhibited 50% effective concentration (EC50) values for tetraconazole of <0.01 (Jg ml"', whereas no isolates could be found in this EC50 range in 2010. Since 2007, annual median and mean tetraconazole EC50 values have generally been increasing, and the frequency of isolates with EC50 values >0.11 lig ml-' increased from 2008 to 2010. In contrast, the frequency of isolates with EC50 values for prothioconazole of >1.0 ng mh' has been decreasing since 2007. Annual median difenoconazole EC50 values appears to be stable, although annual mean EC50 values generally have been increasing for this fungicide. Although EC50 values are important for gauging fungicide sensitivity trends, a rigorous comparison of the relationship between in vitro EC50 values and loss of fungicide efficacy in planta has not been conducted for C. beticola. To explore this, 12 isolates exhibiting a wide range of tetraconazole EC50 values were inoculated to sugar beet but no tetraconazole was applied. No relationship was found between isolate EC50 value and disease severity. To assess whether EC50 values are related to fungicide efficacy in planta, sugar beet plants were sprayed with various dilutions of Eminent, the commercial formulation of tetraconazole, and subsequently inoculated with isolates that exhibited very low, medium, or high tetraconazole EC50 values. The high EC50 isolate caused significantly more disease than isolates with medium or very low EC50 values at the field application rate and most reduced rates. Because in vitro sensitivity testing is typically carried out with the active ingredient of the commercial fungicide, we investigated whether loss of disease control was the same for tetraconazole as for the commercial product Eminent. The high EC50 isolate caused more disease on plants treated with tetraconazole than Eminent but disease severity was not different between plants inoculated with the very low EC50 isolate.Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola (Sacc), is the most important foliar disease of sugar beet {Beta vulgaris L.) in North Dakota and Minnesota (39). The disease causes a reduction in root har...

show abstract