Effects of oxalic acid and culture filtrate of Sclerotinia sclerotiorum on metabolic changes in sunflower evaluated using FT-IR spectroscopy

Sclerotinia sclerotiorum: (Lib.) de Bary is an important plant pathogenic fungus with a very wide host range. A virulence factor of many necrotrophic pathogens, including S. sclerotiorum, is oxalic acid (OA), which can disrupt plant cell wall integrity by chelating cell wall Ca2+ and acidifying host cells. Fourier transform-infrared (FT-IR) spectroscopy, a powerful method to analyze chemical changes during plant-pathogen interactions, was used here to study metabolic changes in the stem of sunflower inbred lines after treatment with either synthetic OA or the fungal culture filtrate to further clarify the roles of OA in the infection process of S. sclerotiorum. The relative absorbance ratio of carbohydrate to lignin and main subunits of lignin also were calculated from the spectra. Principal component analysis and relative absorbance ratios were applied to find differences between the spectra of control and treated plants. Although the peak patterns of the spectra were common among all treatments, the peak intensities differed, and a shift to a longer or lower wavenumber of the bands was observed. The result of this study showed that, in addition to OA, other virulence factors may have key roles during pathogenesis of S. sclerotiorum and could facilitate the development of pathogen in plant tissues.