Inhibitory Influence of Organic and Inorganic Sodium Salts and Synthetic Fungicides Against Bean Root Rot Pathogens

The efficacy of 20 organic and inorganic sodium salts, and two synthetic fungicides against eight bean root rot pathogens—Fusarium equiseti, F. proliferatum, F. semitectum, F. solani f. sp. phaseoli, F. verticillioides, Rhizoctonia solani AG4–HG I, Macrophomina phaseolina and Sclerotium rolfsii—were evaluated in this study. Accordingly to preliminary in vitro tests, only captan, benzoate and metabisulfite (2 %) were able to completely inhibit mycelial growth of all eight fungi. Moreover, no significant differences were observed among the inhibitory effect of these three compounds and EDTA (P ≤ 0.05). With few exceptions, the ED₅₀ values indicated captan to have a greater effect against fungi than benzoate, EDTA and metabisulfite. However, captan, benzoate and EDTA all had MIC values that varied greatly from that of metabisulfite. Whereas captan, benzoate and EDTA showed fungitoxic activity against all fungi tested at concentrations greater than 0.1 %, metabisulfite showed fungitoxic activity against all fungi tested at concentrations of 0.025–0.25 %. Soil bioassays showed 0.25 % metabisulfite to completely inhibit mycelial growth of F. proliferatum, F. semitectum, R. solani AG–4 HG I, M. phaseolina and S. rolfsii, but not F. equiseti, F. solani f. sp. phaseoli and F. verticillioides. Higher concentrations of captan and benzoate were required to achieve total inhibition in soil bioassays when compared to metabisulfite, whereas EDTA was not able to completely inhibit growth of any of the fungi tested, even at the highest concentration. Moreover, the application of 1.0–2.0 % EDTA was found to be phytotoxic to bean seeds in terms of both seed germination and root elongation, whereas 0.1–0.75 % captan, 0.1–0.75 % benzoate and 0.1 % metabisulfite did not exhibit any phytotoxicity in terms of germination; 0.5 % captan, 0.1 % benzoate and 0.1 % metabisulfite did, however, have a negative effect on root elongation.

The results of pH studies also demonstrated all eight fungi tested to be capable of growth in both acidic and basic environments, although the growth of some species was inhibited at the lowest value tested (pH 2), and the growth of all species was totally inhibited at the highest value tested (pH 12).