Action of selenium against Sclerotinia sclerotiorum: Damaging membrane system and interfering with metabolism.

Selenium (Se) in soil is beneficial for environmental stress tolerance of plants, and it has widespread toxic effects on pathogens. Based on the fact that Se significantly inhibited the growth of Sclerotinia sclerotiorum, we set experiments with different concentrations of Se to investigate the action of Se against S. sclerotiorum in this study. The results showed that Se (>0.5 mg L-1) changed the morphology of S. sclerotiorum mycelia, and higher Se concentrations severely damaged mycelial structures. Fourier transform infrared spectroscopy (FTIR) analysis indicated that Se treatment induced the chemical composition of mycelia with much abundance of functional groups such as alcohols, ketones, ammonium and esters, and 0.5 mg L-1 Se maximized their concentrations. Under Se treatments, the electrical conductivity of mycelia increased in a time-dependent manner, and osmolyte concentrations of mycelia increased as well. Se supplementation significantly reduced polymethylgalacturonase (PMG) and carboxymethylcellulase (Cx) activities, which protecting plants from infection, and increased the energy expenditure in S. sclerotiorum. Combined action of Se damage on membrane system, osmoregulation, reduction of cell wall degrading enzymes activities and improvement of energy expenditure resulted in the inhibition of S. sclerotiorum growth. Findings in this study provided evidences for using Se as a potential fungicide to control S. sclerotiorum.