Studies on the identification of suitable solvents for microbial bioassay

The toxicity of five organic solvents, viz. N,N-dimethylformamide (DMF), dimethyl sulphoxide (DMSO), 1,4dioxan, formamide and N-methyl-2-pyrrolidone was evaluated against Colletotrichum capsici, Drechslera oryzae, Fusarium oxysporum f. sp. cubense, Pyricularia oryzae, Pythium aphanidermatum and Rhizoctonia solani through poisoned agar bioassay. N-methyl-2-pyrrolidone was found to be the most toxic solvent with EC₅₀ values of 0.36, 0.70, 0.87, 0.29, 0.83 and 0.36% for the test fungal organisms respectively. DMSO showed the least toxicity with EC₅₀ values of 2.91, 3.43, 4.78, 1.46, 3.63 and 1.93% respectively. DMF, formamide and 1,4-dioxan exhibited moderate toxicity. Among the test fungi, P. oryzae was the most sensitive with least EC₅₀ values and F. o. cubense was the least sensitive with high EC₅₀ values to all the solvents.