Phytopathology reagents - Guaiacol
Guaiacol is commonly used in colorimetric assays to measure peroxidase enzyme activity. Initially colorless, guaiacol undergoes polymerization in the presence of a peroxidase and H2O2 to form a brown compound known as tetraguaiacol which can be measured spectrophotometrically at roughly 470 nm (Johannes, 2006; Doerge, 1997; Balešević-Tubić, 2011). Guaiacol has also been documented to detect Helminthosporium oryzae and Trichoconis padwickii in rice seeds when incorporated into an agar medium with streptomycin by staining the surrounding medium red in the presence of the fungus (Kulik, 1975). Medium components according to Kulik (1975) are 0.125g guaiacol, 5g agar & 0.5g streptomycin (added after autoclaving) per liter of water. In soybean seed testing, guaiacol separates different cultivars based on high and low seed coat peroxidase activity. The level of peroxidase activity of the seed coat is based on the color change of the guaiacol (Schmitz, 1997).