LAUSR

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 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 mitochondrial tricarboxylic acid (TCA) cycle of PYR-treated B. cinerea is analyzed. The results show that PYR-A to H have their own unique character of XRPD patterns, but crystal morphology of eight PYRs presents in triclinic crystal system and space group P-1(-). 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 EC50 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 anti-conformation 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.