Inhibitory mechanism of cantharidin derivatives against Sclerotinia sclerotiorum

In order to investigate the antifungal activities and the inhibitory mechanism of cantharidin derivatives against Sclerotinia sclerotiorum, the inhibitory effects of five halogenated aromatic amines( BY , BY-1 , BY-2 , BY-3 and BY-4 ) on the mycelial growth and the sclerotia formation of S. sclerotiorum were determined. The relative control efficacy against Sclerotinia rot on detached leaves of rapeseed and the antifungal mechanism of cantharidin derivatives were analyzed by measuring the mycelial morphology, the mycelial relative conductivity, the malondialdehyde content, the reduction of sugar content and soluble protein content, the activity of chitinase and the content of oxalic acid in the hypha treated with cantharidin derivatives. The results showed that five cantharidin derivatives significantly inhibited the mycelial growth of S. sclerotiorum, and the EC₅₀ values of BY , BY-1 , BY-2 , BY-3 and BY-4 were 37.6, 8.78, 6.45, 12.2 and 50.4 μg/mL, respectively. The inhibitory effect of the derivative BY-2 on sclerotia formation was the strongest. And the inhibition rate was 86.52% at the concentration of 12.5 μg/mL. The treatment of the detached rapeseed leaves with the derivative BY-2 (100 μg/mL) afforded 97.71% relative control efficacy. These results indicated that the introduction of a chlorine atom at the C-3′ site of benzene ring could significantly improve the inhibitory activity of cantharidin against S. sclerotiorum. After the hypha was treated with cantharidin derivatives, the surface of mycelia turned rough, or dehydrated and shriveled, or deformed and expanded. The cell membrane permeability was increased, and the reducing sugar content and soluble protein content were decreased. Furthermore, the chitinase activity was also increased, and oxalic acid content was significantly decreased. Above all, the results showed that the cantharidin derivatives could effectively prevent and cure Sclerotinia stem rot, and provided theoretical basis for the development of biological fungicide.