Relationship of Resistance to Benzimidazole Fungicides with Mutation of β-Tubulin Gene in Venturia nashicola

Pear scab caused by Venturia nashicola has been reported as an important disease of pear resulting in lowering the quality of pear fruits. In this study, it was conducted to investigate the relationship between resistance of V. nashicola and mutation of ${\beta}$-tubulin gene and the fungicide resistance in field isolate group in benzimidazole fungicides. Responce of V. nashicola to carbendazim could be classified into 3 groups as sensitive that does not grow at all on PDA amended with $0.16{\mu}g/ml$ of carbendazim, low resistance that could not grow in $4.0{\mu}g/ml$ medium, and high resistance that can grow even at $100{\mu}g/ml$. Thirty isolates of V. nashicola collected from 3 regions as Wonju, Naju, and Okcheon were highly resistant to carbendazim. Analysis of the nucleotide sequence of ${\beta}$-tubulin gene of V. nashicola showed that there was no difference in the nucleotide sequence between the sensitive and the low-resistant isolate, but GAG at codon 198 (glutamic acid) was replaced with GCG (alanine) in the high-resistant isolate. Among 10 isolates obtained from the Okcheon, 5 isolates showed the substitution of glycine for glutamic acid, which were resistant to carbendazim, but more sensitive to the mixture of carbendazim and diethofencarb than others. Through these results, all isolates of V. nashicola isolated in pear orchard were found to be resistant to benzimidazoles. Also, mutants E198A and E198G at ${\beta}$-tubulin were found to be important mechanisms of V. nashicola resistance against benzimidazole fungicides.

Benzimidazole계 살균제에 대한 배 검은별무늬병균 Venturia nashicola 의 저항성과 β-Tubulin 유전자 돌연변이와의 관계

Benzimidazole계 살균제 저항성을 모니터링하면서, 저항성과 ${\beta}$-tubulin 유전자의 198번째 코돈의 돌연변이와의 관계를 조사하였다. Venturia nashicola의 benzimidazole계 살균제에 대한 반응은 $0.16{\mu}g/ml$ carbendazim 배지에서 전혀 생장하지 못하는 감수성과 $4.0{\mu}g/ml$ 배지에서 생장이 안 되는 저저항성, $100{\mu}g/ml$에서조차 생장이 가능한 고저항성으로 구분할 수 있었다. 국내 3개 지역의 과원에서 채집한 30균주의 V. nashicola는 carbendazim에 대해서 모두 고저항성이었다. V. nashicola의 ${\beta}$-tubulin 유전자의 염기서열을 분석한 결과 저저항성 균주에서는 감수성 균주와 염기서열에 차이가 없었지만, 고저항성 균주는 GAG인 glutamic acid가 GCG인 alanine으로 치환되어 있었다. 옥천의 과원에서 분리한 10균주 중에서 5균주는 GGG인 glycine으로 치환되어 있었다. 특히 glycine으로 치환될 경우 carbendazim에 대해서 저항성이 되면서 carbendazim과 diethofencarb 혼합제에 대해서는 감수성이 더 커졌다. 결국 ${\beta}$-tubulin의 198번째 코돈의 돌연변이 E198A와 E198G는 V. nashicola가 benzimidazole계 살균제에 대해서 저항성이 되는 중요한 기작임을 알 수 있었다.