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Poster: Biology & Disease Mgmt: Chemical Control


Assessment of QoI Resistance in Colletotrichum spp. Isolated from Boxthorn and Apple in Korea
S. KIM (1), J. Min (1), D. Back (1), H. Kim (1), S. Lee (1), K. Kim (1) (1) Chungbuk National University, Korea

Strobirulin fungicides including azoxystrobin, krezoxim-methyl, and pyraclostrobin are inhibitors of mitochondrial respiration; they inhibit the cytochrome bc1 enzyme complex at the Qo site (quinone outside inhibitors, QoIs). QoI resistance has been reported in many pathogens such as Blumeria gramins f. sp. tritici, Plasmopara viticola and so on. The primary molecular mechanism of QoI resistance is a point mutation at codon 143 based on the substitution of glycine by alanine(GGT to GCT, G143A) in the mitochondrial-encoded cytochrome b gene. We examined the sensitivity of Colletotrichum spp. isolated from boxthorn fields and apple orchards to pyraclostrobin through the mycelial growth inhibition test on PDA amended with the fungicide. The resistance of C. acutatum isolates from boxthorn was determined with values of EC50 (effective concentration reducing the mycelial growth by 50%). The EC50 of resistant isolates was more than 1.7µg/ml. On the other hand, The EC50 of sensitive isolates of C. gloeosporioides from apples was determined as less than 0.24µg/ml, whereas resistant isolates were more than 66.9ug/ml. The codon 143 of cytochrome b gene was substituted from GGT to GCT in all of resistant isolates regardless of Colletotrichum species. For the successful control of anthracnose in boxthorn fields or apple orchards in Korea, it is required a monitoring of the QoI resistance with an allele-specific PCR with primers generated from the 143 codon substitution.