Determining Fitness Cost in Qoi-Resistant Isolates of the Frogeye Leaf Spot Pathogen
Brochard, Nicole Rochelle
Allen, Thomas W.
CommitteeMelanson, Rebecca A.
Frogeye leaf spot is a foliar disease of soybean caused by Cercospora sojina Hara, which until recently had been successfully managed by quinone outside inhibitor (QoI) fungicides. After widespread resistance to the QoI fungicides was reported throughout Mississippi, the next step in characterizing C. sojina was to study the fitness of selected isolates. Fitness measurements of resistance stability, colony growth, conidia production and germination, and virulence were assessed. A phylogenetic analysis was also conducted to assess the genetic similarity of the QoI-resistant and -sensitive C. sojina isolates. All isolates remained stable in terms of QoI resistance. Results of all fitness measurements indicated no significant differences between the QoI-resistant and -sensitive C. sojina isolates. The phylogenetic analysis supported these results revealing similarity between QoI-resistant and -sensitive C. sojina isolates. Based on these results no indication of a fitness cost is associated with QoI resistance in C. sojina isolates from Mississippi soybean.