水稻稻瘟病菌对烯肟菌胺的抗性风险评估及抗性机制初探

Risk assessment and molecular mechanism of the resistance of Magnaporthe oryzae from rice to SYP-1620

采用菌丝生长速率法测定了100株采自我国主要水稻产区的水稻稻瘟病菌对烯肟菌胺的敏感性，结果表明，其EC50分布于0．0111-0．2956μg·mL-1，平均EC50=（0．0786±0．0561）μg·mL-1。供试菌株对烯肟菌胺的敏感性分布呈单侧峰曲线，未出现抗药性亚群体，可将该曲线作为稻病瘟菌对烯肟菌胺的敏感性基线。通过室内药剂驯化获得了7株抗药突变体，突变频率为1．11×10^-4，其中2株高抗突变体NJ0811-I和A10的抗性水平大于1000倍，抗药性性状能稳定遗传，致病力显著弱于其亲本菌株；5株低抗突变体抗性水平在2．05～4．55倍之间，抗药稳定性差，适合度与亲本无显著性差异。交互抗药性结果表明，烯肟菌胺与嘧菌酯存在正交互抗药性，与田间防治稻瘟病常用药剂稻瘟灵、异稻瘟净无交互抗药性。综合分析表明，稻瘟病菌对烯肟菌胺可能存在低到中等抗性风险。进一步克隆了抗药突变体及其亲本的cytb基因，CYTB氨基酸序列比对结果表明，2株高抗突变体均在143位由甘氨酸突变为丝氨酸（G143S），建立了高抗菌株的AS．PCR分子检测方法；而5株低抗突变体cytb基因未发生点突变，推测可能存在其他的抗性分子机制。

The sensitivities of 100 Magnaporthe oryzae isolates from the main rice production areas in China to SYP-1620 were determined by colony diameter assay. The results showed that the EC50 values were distributed in 0.011 1-0.295 6 μg .mL-2. The mean EC50 value was （0.078 6±0.056 1） μg . mL-1. The sensitivity frequency of M. oryzae to SYP-1620 distributed as a unilateral peak curve, which showed that there was no resistant sub- population among these strains, and could be used as baseline-sensitivity for field resistance monitoring of M. oryzae to SYP-1620. Two highly resistant mutants and five low resistant mutants were obtained by fungicide ad- aptation at a mutation frequency 1.11×10-4. The highly resistant mutants showed stable resistance factors were a- bove 1 000 folds, but the low resistant mutants which resistance factors were 2.05 to 4.55 folds and unstable. As compared to parent isolates, the virulence on rice leaves of the two highly resistant mutants exhibited significant- ly decreased. However, there was no significant difference of fitness between the five low resistant mutants and their parent isolates. Cross-resistance studies showed that there was positive cross resistance between SYP-1620 and azoxystrobin, but no correlationship between SYP-1620 and iprobenfos, isoprothiolane. Based on the signifi- candy impaired fitness, the field resistance risk of M. oryzae to SYP-1620 might be low to moderate. The cytb gene was cloned from the mutants and parent isolates. One single-point mutation was found in CYTB at aminoacid position 143 from glycine to serine （ G143S ）, which might be the resistant molecular mechanism of M. oryzae to SYP-1620. The AS-PCR was developed to detect the G143S mutants in field. There was no mutation in cytb gene of the low resistant mutants.