Abstract
The fungicide SYP-14288 has a high efficiency, low toxicity, and broad spectrum in inhibiting both fungi and oomycetes, but its mode of action (MoA) remains unclear on inhibiting fungi. In this study, the MoA was determined by analyzing the metabolism and respiratory activities of Rhizoctonia solani treated by SYP-14288. Wild-type strains and SYP-14288-resistant mutants of R. solani were incubated on potato dextrose agar amended with either SYP-14288 or one of select fungicides acting on fungal respiration, including complex I, II, and III inhibitors; uncouplers; and ATP synthase inhibitors. Mycelial growth was measured under fungicides treatments. ATP content was determined using an ATP assay kit, membrane potential of mitochondria was detected with the JC-1 kit, and respiratory rate was calculated based on the measurement of oxygen consumption of R. solani. A model of metabolic fingerprinting cluster was established to separate oxidation inhibitors and phosphorylation inhibitors. All the results together displayed a clear discrimination between oxidation inhibitors and phosphorylation inhibitors, and the latter inhibited ATP synthase production having or uncoupling activities. Based on the model, SYP-14288 was placed in phosphorylation inhibitor group, because it significantly reduced ATP content and membrane potential of mitochondria while increasing respiratory rate in R. solani. Therefore, the MoA of SYP-14288 on R. solani was confirmed to involve phosphorylation inhibition and possibly uncoupling activity.
Highlights
The soil-borne fungus Rhizoctonia solani is a ubiquitous plant pathogen that attacks almost all known crops, pastures, and horticultural species, leading to significant yield losses (El-Samawaty et al, 2012; Constable and Bange, 2015; Anderson et al, 2016; Ajayi-Oyetunde and Bradley, 2018)
Total ion chromatograms (TIC, Supplementary Figure 1) showed a significant difference of metabolic fingerprinting between control group and the fungicide treatment with relative standard deviation (RSD) of the internal standard substance salicin of 3.2%, indicating an acceptable stability of the method
Different metabolites with significant changes in R. solani were observed when treated with respiratory inhibitor, and an hierarchical cluster analysis (HCA) of respiratory inhibitors was performed according to these compounds (Figure 1)
Summary
The soil-borne fungus Rhizoctonia solani is a ubiquitous plant pathogen that attacks almost all known crops, pastures, and horticultural species, leading to significant yield losses (El-Samawaty et al, 2012; Constable and Bange, 2015; Anderson et al, 2016; Ajayi-Oyetunde and Bradley, 2018). Co., Ltd., Shenyang, China), exhibits a high level of fungitoxicity against R. solani and many other pathogens (Lan et al, 2012; Cai et al, 2019) Since it has been internationally patented, we anticipate that it will have great potential use and large market share for field disease control (Zhang and Liang, 2017). A previous study had shown that SYP-14288 influenced the respiratory process and inhibited ATP biosynthesis in Phytophthora capsici (Wang et al, 2018), but further investigation is still needed, especially on different pathogens, such as R. solani. This is because P. capsici belongs to oomycetes, but R. solani is a member of true fungi. The MoA of SYP-14288 on R. solani needs to be confirmed
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