Fusarium oxysporum isolates showed varied benzimidazole fungicides sensitivity under low temperature and heavy metal stress

Abstract

Emergence of fungicide resistant phytopathogens under changing environmental condition is a serious problem in agriculture. Four Fusarium oxysporum isolates were isolated from four wilted crop plants (tomato, potato, pea and grass pea) and identified through conidial morphology and rDNA sequence analysis. Sensitivity of carbendazim and thiophanate methyl was tested through estimation of radial growth based ED50 values and conidia germination based EC50 values. The isolates were able to grow in presence of carbendazim (1.2 mg/L) with ED50 values ranging from 0.62 to 0.97 mg/L and EC50 values ranging from 0.10 to 1.13 mg/L. Moreover, they could also tolerate thiophanate methyl (upto 100 mg/L) with ED50 values ranging from 12.5 to 30.6 mg/L and EC50 values ranging from 23.0 to 43.0 mg/L. Thiophanate methyl was less effective to inhibit conidial germination under in vitro condition. The isolates were also showed pleiotropic inhibitory effect on mycelia growth to carbendazim (1 mg/L) and thiophanate methyl (10 mg/L) at low temperature. They could tolerate heavy metals such as arsenic, cadmium and lead (each at 100 mg/L concentration). Metal supplementation increased carbendazim sensitivity, but decreased thiophanate methyl sensitivity. Spectrophotometric analysis revealed that the suppressed activity of thiophanate methyl was due to interaction with the metals, but no such interactions occurred with carbendazim. Thus, under low temperature and heavy metal stress, carbendazim might be used judiciously for control of the pathogen.