Alternative and safe dyes for staining Arbuscular Mycorrhizal fungi

Several methodologies are available for the study of Arbuscular Mycorrhizal fungi (AM). Most involving the colouring of typical symbiosis structures, with the use of dyes such as Trypan Blue, which can be harmful to users' health (e.g., carcinogens) and the environment (e.g., pollutants). In order to use safe alternatives for AM fungi studies, a comparison and analysis of the use of industrial organic food dyes (Arcólor®) in blue and red colours, organic dye based on Euterpe oleracea Mart. pulp (açaí) and the traditional Trypan Blue (control), all of them diluted in commercial vinegar, for observation and quantification of the typical structures of mycorrhizal infection in the roots of Vigna unguiculata L., Schizolobium amazonicum Huber ex Ducke, Zea mays L. and Brachiaria sp. The results indicated that the organic dyes visually colour the structures of the AM fungi. However, blue food colouring is as effective as Trypan Blue, in addition to being a good option in teaching activities evolving AM fungi, mainly because it presents less risk to users' health. Thus, a good substitute for the Trypan Blue synthetic dye is presented, based on an effective, easily applicable, low cost and safe methodology for the study and teaching of AM fungi.