Changes in Cytochrome b Gene Expression in Cochliobolus sativus Induced by Triadimefon, a Triazole Fungicide

Introduction: Spot blotch (SB), caused by Cochliobolus sativus, is most effectively managed using fungicide applications, including triadimefon (TDM) a triazole compound. C. sativus posses a great concern as it might develop resistance against fungicides like TDM due to its high genetic variability, short life cycle and abundant inoculum production. Therefore, to better understand the mechanisms of TDM resistance initiated by C. sativus, changes in cytochrome b (cytb) gene in virulent and avirulent pathotypes were evaluated at early time points of TDM treatments. Materials and Methods: C. sativus sensitivity to TDM was determined by measuring radial growth of each pathotype on PDA plates. Additionally, RNA was isolated from mycelia of each pathotype at 24, 48, 72 and 96 hours post fungicide treatments and used for cDNA synthesis. Cytb was verified using quantitative reverse transcriptase PCR (qRT-PCR). Results: Data showed that the maximum mycelial growth inhibition by 50% (EC50) for both pathotypes was recorded 48 hours at 0.25 µg mL^-1 TDM treatment. The qRT-PCR revealed that cytb expression increased in both virulent and avirulent pathotypes at 24 hours post TDM treatments in comparison with non-treated controls. The most outstanding differences in cytb expression were 7.69 and 2.88-fold in the virulent and avirulent pathotypes, respectively, 48 hours of 0.25 µg mL^-1 TDM treatment. Conclusions: According to findings, it is possible to propose that cytb gene might play a role in signaling events during C. sativus exposure to commercial triazole fungicide.