Baseline Sensitivity of Pyraclostrobin and Toxicity of SHAM to Sclerotinia sclerotiorum

Abstract

Sclerotinia sclerotiorum is a cosmopolitan plant pathogen notable for its wide host range. The quinone outside inhibitor (QoI) fungicide pyraclostrobin has not been registered for control of S. sclerotiorum in China. In this study, baseline sensitivity of pyraclostrobin was established based on effective concentration for 50% inhibition of mycelial growth (EC50) values of 153 isolates of S. sclerotiorum collected from five provinces of China and toxicity of alternative oxidase inhibitor salicylhydroxamic acid (SHAM) to S. sclerotiorum was determined. Results showed that the frequency distribution of EC50 values of the 153 isolates was unimodal but with a right-hand tail. The mean EC50 value was 0.1027 μg/ml and the range of EC50 values was 0.0124 to 0.6324 μg/ml. Applied as a preventive fungicide in pot experiments, pyraclostrobin at 5, 15, and 45 μg/ml provided control efficacies of 61, 77, and 100%, respectively. There was no positive cross-resistance between pyraclostrobin and carbendazim or dimethachlon. EC50 values for SHAM against four isolates of S. sclerotiorum were 44.4, 51.8, 54.4, and 68.7 μg/ml. SHAM at 20 μg/ml could significantly increase not only the inhibitory effect of pyraclostrobin on mycelial growth on potato dextrose agar media but also the control efficacy in planta. These results indicated that SHAM should not be added into artificial media in in vitro assay of S. sclerotiorum sensitivity to pyraclostrobin. This has broad implications for assay of sensitivity of fungal pathogen to QoI fungicides.

The cytochrome bc1 complex as an antipathogenic target

“…SHAM is a relatively poor inhibitor of the AOX, with an inhibition constant ( K i ) of 21 μ m against the Trypanosoma brucei enzyme (as measured by glycerophosphate‐linked oxygen uptake assay) [81]. As an antifungal agent, SHAM has also been observed to act synergistically with QoIs in vitro , but this response is species (and QoI)‐dependent [65,70,82]. Unfortunately, SHAM is a relatively nonspecific inhibitor and poorly taken up by plants, and so is unsuitable for use in the field [70].…”

Dual-active antifungal agents containing strobilurin and SDHI-based pharmacophores

“…However, the use of SHAM in vitro is controversial. In fact, it was shown that in some pathogens AOX is active also in planta , therefore questioning the use of SHAM in vitro to suppress AOX, as it could lead to overestimation of QoI activity 24 . Moreover, inhibitory effect of SHAM on the growth of some fungal pathogens was observed 25,26 , and therefore we evaluated the effect of novel dual compounds and commercial fungicides without the addition of SHAM.…”

Diagnosis and Integrated Management of Fruit Rot in Cucurbita argyrosperma, Caused by Sclerotium rolfsii

“…These results were possible because metalaxyl belongs to the phenylamides group, which inhibits the synthesis of ribonucleic acid (RNA), affecting mycelial growth, spore formation and pathogen infection (Fishel and Dewdney, 2012). Liang et al (2015) evaluated the effect of pyraclostrobin on Sclerotinia sclerotiorum , and reported that close to 100% inhibition was obtained when using salycilhydroxamic acid. Without the latter, the inhibition was significantly reduced.…”