Development of Fungicidal Resistance in Pyricularia grisea Inducing Rice Blast to Carbendazim

Rice blast incited by Pyricularia grisea (telemorph: Magnaporthe grisea) is one of the economically important diseases. Nine isolates (Pg₁ to Pg₉) of P. grisea were tested in vitro at different concentrations of carbendazim (02000 mg ml⁻¹) by adopting poisoned food technique for development of resistance. The isolate Pg₁ recorded the highest ED₅₀ value of 4.05 fig ml⁻¹ and Pg₉ recorded the lowest ED₅₀ value of 2.82 jg ml⁻¹ and MIC value of both was 10 jg ml⁻¹ which was nearly equal sensitive as reference isolate Pg₂ Isolate Pg₃ recorded the next lowest ED₅₀ value of 2.98 jg ml⁻¹ with MIC of 10 jg ml⁻¹ followed by isolates Pg₄ with ED₅₀ value of 3.32 jg ml⁻¹ and Pg₅ with ED₅₀ value of 3.35 in the increasing order of their resistance. The MIC values of both isolates Pg₄ and Pg₅ were 10 jg ml⁻¹. Pg₈ isolate recorded the next highest ED₅₀ value of 3.6 jg ml⁻¹ with MIC of 10 jg ml⁻¹ followed by Pg₆ isolate (3.43 jg ml⁻¹) and Pg₇ isolate (3.39 jg ml⁻¹) in the decreasing order of their resistance. The MIC value for both Pg₆ and Pg₇ isolates was 10 jg ml⁻¹. The results indicated that the fungus is under high selection pressure leading to evolution of carbendazim resistant population.