Fungitoxicity and Quantitative Structure Activity Relationship Study of Aryl Carboxylic Acids

Twenty eight differently substituted aryl carboxylic acid were evaluated in vitro for fungicidal activity against six fungi viz. Rhizoctonia solani, Sclerotium rolfsii, Rhizoctonia bataticola, Pythium. aphanidermatum, Fusarium oxysporum and Alternaria alternata. Few of these acids exhibited good activity. Among all, the 2-CH₃ substituted acid (ED₅₀=126 μg/ml) against R. solani, 3,5-(NO₂)₂, 2-OH (ED₅₀=198 μg/ml) against S. rolfsii, 3-CH₃ (ED₅₀=146 μg/ml) against P. aphanidermatum and 2-SH against R. bataticola (ED₅₀=82 μg/ml), F. oxysporum (ED₅₀=43 μg/ml) and A. alternata (ED₅₀=95μg/ml) exhibited the highest fungicidal activity. The quantitative structure activity relationship (QSAR) study using the in vitro fungicidal activity data and physico-chemical parameters of phenyl ring substituents for hydrophobic, electronic and steric properties by means of multiple regression analysis has revealed that the fungicidal activity of aryl carboxylic acids against all the test fungi was dependent on position dependent steric effect of the substituents. The fungicidal activity against S. rolfsii, F. oxysporum and A. alternata also positively depended on electronic effect of ortho substituents and against R. bataticola on hydrophobicity.