Fungicidal Activity and Quantitative Structure Activity Relationship of O,O-Diaryl O-Ethyl Phosphorothionates

A series of twenty-one O,O-diaryl O-ethyl phosphorothionates have been tested in vitro for fungitoxicity against five fungi viz. Rhizoctonia bataticola, Alternaria alternata, Fusarium oxysporum, Pythium aphanidermatum and Drechslera oryzae. O,O-Di (pentachlorophenyl) O-ethyl phosphorothionate was identified as potential broad spectrum fungicide, as it exhibited excellent activity against R. bataticola (ED₅₀ 0.015 mg mL⁻¹) and comparativele better activity against other test fungi. The quantitative structure activity relationships study revealed different structural requirement for fungitoxicity against each of the test fungus. The position dependent steric effect of the phenyl substituents was important for the fungitoxicity against R. bataticola and A. alternata and hydrophobicity for F. oxysporum, P. aphanidermatum and D. oryzae.