Stimulatory Effects of Sublethal Doses of Dimethachlon on Sclerotinia sclerotiorum

Abstract

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...

Stimulatory Effects of Boscalid on Virulence of Sclerotinia sclerotiorum Indicate Hormesis May Be Masked by Inhibitions

“…Hormesis is a generalizable biological concept, and the quantitative features of hormesis are consistent across a broad range of biological models and independent of chemical stressors, with the maximum stimulation magnitude being about 30-60% compared with the control (Calabrese 2015a). However, our previous study showed that the virulence stimulation magnitude of S. sclerotiorum by dimethachlone varied considerably and it seemed that larger stimulation magnitudes were obtained for dimethachlone-resistant isolates which usually have reduced virulence (Zhang et al 2019;Zhou et al 2014a). Therefore, the present study employed a group of S. sclerotiorum isolates with different levels of virulence to determine the correlation of the maximum stimulation magnitudes with virulence, and a significant negative correlation with P = 0.019 and R 2 = 0.439 was obtained.…”

“…Given the unavoidable experimental random errors, smaller stimulation magnitude implies it is more difficult to obtain statistically significant stimulations. Previously, we have reported considerable stimulatory effects of dimethachlone on mycelial growth of dimethachlone-resistant isolates of S. sclerotiorum (Zhou et al 2014a). The greater mycelial growth stimulation magnitude of dimethachlone-resistant isolates may be related to the reduced mycelial growth rates compared with sensitive isolates (Zhou et al 2014b).…”

“…There have been numerous reports on fungicide hormesis, such as stimulatory effects of metalaxyl, mefenoxam, propamocarb, and cyazofamid on plant-pathogenic oomycetes Pythium aphanidermatum and Phytophthora infestans (Garzón et al 2011;Zhang et al 1997), and thiabendazole and thiophanate-methyl on fungal pathogens Penicillium expansum (Baraldi et al 2003) and Sclerotinia homoeocarpa (Pradhan et al 2019). In addition, our laboratory reported hormetic effects of carbendazim (Di et al 2015b), dimethachlone (Zhou et al 2014a), flusilazole (Lu et al 2018a, b), prochloraz (Zhang et al 2019), and trifloxystrobin (Di et al 2016a) on the pathogenicity of S. sclerotiorum.…”

The Role of Heavy Metals in Plant Response to Biotic Stress

“…Also, the mycelial growths of fungi such as Lyophyllum palustre (Peck) Singer [ 241 ] and Phythium aphanidermatum , P. irregular and P. ultimatum were increased by propamocarb [ 242 ]. Besides, Phytophthora infestans growth increased as a result of the impact of metalaxyl [ 243 ] and Sclerotinia sclerotiorum under treatment with dimethachlon conditions [ 244 ].…”

Biological control of the soil-borne fungal pathogen Sclerotinia sclerotiorum –– a review

“…Several chemical agents registered in the USA, Canada, Australia, Europe and China are available to this purpose. Their active ingredients are: boscalid, fluazinam, fluxapyroxad, pyraclostrobin, penthiopyrad, picoxystrobin, prothioconazole, prothioconazole and trifloxystrobin, tetraconazole, thiophanate methyl (Matheron and Porchas 2004;Bradley et al 2006;Zhou et al 2014aZhou et al , 2014bWang et al 2015;Derbyshire and Denton-Giles 2016). The effective control of S. sclerotiorum requires application of fungicides during sensitive time frames, the number of treatments depending on the length of the crop vegetation period and on how long flowers or petals are available for infection by ascospores (Heffer Link and Johnson 2007).…”