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BACKGROUNDSclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum threatens oilseed rape cultivation, and the emergence of fungicide‐resistant strains has led to control failures worldwide. Identifying novel chemical alternatives with different modes of action and high antifungal activities is thus crucial. Herein we evaluated the antifungal effects of 3‐(2‐pyridyl)methyl‐2‐(4‐chlorphenyl)imino‐ thiazolidine (PMAS) on S. sclerotiorum to determine its efficacy for SSR management.RESULTSPMAS had an inhibitory effect on mycelial growth; the EC50 values were 17.83 and 21.15 μg mL−1 for the carbendazim‐susceptible strain Ss01 and carbendazim‐resistant strain Hm25, respectively. PMAS treatment changed the color of inhibited mycelia to green, and the hyphae were sustained in the undifferentiated stage. Cysteine supplementation made this green color disappear, whereas methionine enhanced the color. Moreover, PMAS treatment markedly inhibited oxalic acid biogenesis, increased free thiol content in mycelia, and weakened the activities of oxaloacetase and malate dehydrogenase, but had little effect on the activity of glyoxylate dehydrogenase. Cysteine could reverse the inhibitory effects of PMAS on mycelial morphogenesis and biochemical constituents, except thiol production. In the pot‐culture experiment, PMAS showed a good protective effect, with the control efficacy being >91% on SSR.CONCLUSIONPMAS appears to be an effective fungicide for SSR management. © 2020 Society of Chemical Industry

Pyraclostrobin (PYR) is a commonly used strobilurin fungicide, which inhibits mitochondrial respiration at the ubiquinol oxidation center site of the cytochrome bc1 complex. Little information is available regarding the crystal structure of PYR on its fungicidal effect. In this study, the crystal structures of eight PYRs (PYR-A to H) from different sources are determined by using high-resolution X-ray powder diffraction (XRPD) and model construction with the Pawley refinement module. The effects of PYRs on mycelium growth, the kinetics of mycelial growth, conidial germination, and tube elongation of conidia of Botrytis cinerea from tomato are compared. The level of organic acids in the mitochondrial tricarboxylic acid cycle of PYR-treated B. cinerea is analyzed. The results show that PYR-A to PYR-H have their own unique character of XRPD patterns, but the crystal morphology of eight PYRs presents in the triclinic crystal system and space group P1̅ . PYR-D with the eclipsed conformation and rational edge angles α (72.599°) and β (98.612°) in the crystal cell shows the highest inhibitory effect against mycelium growth with EC 50 as 3.383 μg mL −1 , the best time-dependent effects on the mycelium growth kinetics, and the strongest inhibition on tube elongation of conidia, whereas PYR-E with anticonformation is the worst. Moreover, a significant accumulation of fumarate, malate, and oxalate in the PYR-D-treated mycelium is observed. These findings reinforce the need for a definite crystal structure of PYR to limit usage and mitigate future selection pressure for gray mold management.

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