Sensitivity of field isolates of Botryotinia ricini to fluazinam and thiophanate-methyl

This study aimed to determine the sensitivity of 61 Botryotinia ricini isolates to the fungicides fluazinam and thiophanate-methyl. The isolates were originated from Goias (n = 3), Maranhao (n = 3), Mato Grosso (n = 12), Minas Gerais (n = 1), Paraiba (n = 8), Rio Grande do Sul (n = 19) and Sao Paulo (n = 15) states. Mycelial discs (6 mm) removed from 5-day-old colonies were transferred to Petri dishes containing potato dextrose agar (PDA) amended with different concentrations of the fungicides. Two perpendicular measurements of the radial growth were taken and used to calculate the percentage of mycelial growth inhibition (PMGI) for each treatment (isolate × fungicide × concentration) in relation to the control. PMGI were used to obtain the effective concentration that inhibits 50 and 95% of the mycelial growth (EC50 and EC95) by means of linear regression. For fluazinam, the EC50 and EC95 (mean ± SD) were 0.1738 ± 0.0802 μg/mL and 0.7938 ± 0.1254 μg/mL, while for thiophanate-methyl, the EC50 and EC95 were 0.3487 ± 0.0963 μg/mL and 1.1325 ± 0.2063 μg/mL, respectively. Both fungicides have high intrinsic toxicity to B. ricini but fluazinam was a more potent growth inhibitor compared to thiophanate-methyl.