Study on the Sensitivity of Fusarium spp. Isolates, Causal Agents of Rice Bakanae Disease and Foot Rot to Thiophanate-methyl thiram

Rice Bakanae disease and foot rot caused by Fusarium verticillioides, F. fujikuroi and F. proliferatum, is one of the most important rice seed-born diseases that the best method of its control is seed treatment by fungicides. Fungicide resistance is one of the important subjects that must be studied continuously. In this study, sensitivity of 77 isolates to thiophanate-methyl thiram was investigated in PSA medium amended with 1, 5, 10, 20 and 25 mg/l of thiophanate-methyl thiram active ingredient, after that EC50 and MIC of this fungicide were calculated for each isolate. The results showed that EC50 and MIC of thiophanate-methyl thiram for different isolates were 2.01-6.47 and 5-25 mg/l, respectively. Since the least sensitive isolate was separated from the most sensitive isolate by factor of 3.22 and previous isolates were placed in this range too, therefore it is concluded that resistance to thiophanate-methyl thiram hasn’t appeared in studied populations after almost 10 years of application. There wasn’t any significant difference among mean EC50 of different species, thus their sensitivity range can be expressed as identical EC50 range for three species.