不同温度下两株球孢白僵菌侵染西花蓟马的生长动力学及其毒力

Growth Kinetics and Virulence of Two Beauveria bassiana Strains in Frankliniella occidentalis Under Different Temperatures

【目的】通过比较两株球孢白僵菌(Beauveria bassiana)在不同温度条件下侵染西花蓟马(Frankliniella occidentalis)的生长动力学及其毒力,探讨球孢白僵菌菌体增殖和杀虫毒力的关系,为提高球孢白僵菌对西花蓟马的杀虫效率提供理论支持。【方法】首先,在20、25和30℃3个温度条件下,连续记录第1—8天西花蓟马被两株球孢白僵菌菌株(SCWJ-2和GZGY-1-3)侵染后的死亡率,并以未被真菌感染的西花蓟马为对照,计算其累积校正死亡率,选择第3天的数据(对照死亡率为2%—5%)比较两个菌株的杀虫效率。其次,在20、25和30℃3个温度条件下,连续记录第1—8天内平板培养的上述两个菌株的菌落直径,选取第3天两个菌株的菌落生长直径数据进行比较分析。最后,提取20、25和30℃温度下,西花蓟马分别被两株球孢白僵菌侵染第1、2和3天的混合DNA,通过实时荧光定量PCR(q RT-PCR)技术定量球孢白僵菌在每个宿主样品体内的拷贝数,选取第3天两个菌株的基因拷贝数进行比较分析。【结果】生物测定结果显示,在检测温度(20—30℃)范围内,球孢白僵菌菌株GZGY-1-3和SCWJ-2对西花蓟马成虫均具有较高致病性,无论任何温度和何种菌株,西花蓟马从处理后第2天开始有死亡个体出现,第8天时,SCWJ-2和GZGY-1-3造成的校正死亡率分别为83%—91%和79%—90%。以第3天的校正死亡率为指标(对照死亡率为2%—5%),30℃下菌株SCWJ-2毒力显著高于GZGY-1-3(P<0.05),25℃和20℃下两个菌株毒力无显著差异(P>0.05)。平板培养试验表明,在检测温度(20—30℃)范围内,两个菌株菌落直径随着时间推移而增加,第8天时,菌株SCWJ-2和GZGY-1-3的菌落直径分别为31—36、28—32 mm。选取第3天菌落生长直径数据进行比较,菌株SCWJ-2在3个温度下的菌落直径均显著大于菌株GZGY-1-3(P<0.05)。实时荧光定量结果显示,除30℃下的菌株SCWJ-2之外,两个菌株在西花蓟马体内的基因拷贝数都在第1天时下降,2 d后又逐渐上升。使用第3天西花蓟马体内的基因拷贝数进行分析,在30℃下菌株SCWJ-2真菌拷贝数显著大于GZGY-1-3(P<0.05),25℃和20℃下两个菌株基因拷贝数无显著差异(P>0.05)。【结论】真菌在被侵染虫体内的基因拷贝数受到菌株和温度的影响,这与生物测定结果相一致。与菌株GZGY-1-3相比,SCWJ-2更适合高温条件下对西花蓟马的防治。

【Objective】The objective of this study is to compare the growth kinetics and virulence of two strains of Beauveriabassiana infected Western flower thrips（Frankliniella occidentalis） under different temperatures, analyze the relationship between the proliferation and insecticidal virulence of B. bassiana, and to provide a theoretical support for improving the efficiency of B. bassiana against F. occidentalis.【Method】Firstly, from 1 st to 8 th day, the mortality of the infected F. occidentalis with two strains of B. bassiana（SCWJ-2 and GZGY-1-3） under 20, 25, and 30℃ was recorded, and cumulative corrected mortality was calculated while uninfected F. occidentalis was used as control. The mortality of F. occidentalis infected with the two strains at the 3 rd day（the mortality of control was 2%-5%） was compared. Secondly, under 20, 25 and 30℃, the colony diameter of the two strains was recorded continuously from 1 st to 8 th day. The colony diameter of the two strains at the 3 rd day was compared. Finally, the DNA mixture of F. occidentalis infected with fungi from 1 st to 3 rd day under 20, 25 and 30℃ was extracted, respectively. The real-time fluorescence quantitative PCR（q RT-PCR） was used to quantify the copy number of fungi within each insect host sample. The gene copy of two strains under the same temperature at the 3 rd day was compared. 【Result】The bioassay results of B. bassiana against F. occidentalis showed that within the tested temperature range（20-30℃）, both strains GZGY-1-3 and SCWJ-2 were highly lethal to F. occidentalis adults. No matter what the temperature or the strain, the dead individuals F. occidentalis appeared from the 2 nd day after treatment. On the 8 th day, the corrected mortality of F. occidentalis infected by strain SCWJ-2 and GZGY-1-3 was 83%-91% and 79%-90%, respectively. The corrected mortality of F. occidentalis infected by the two strains on the 3 rd day was compared（the morality of control were 2%-5%）. The virulence of strain SCWJ-2 was significantly higher than that of GZGY-1-3 under 30℃（P〈0.05）, but there was no significant difference between them under 25 and 20℃（P〉0.05）. Within the tested temperature range from 20 to 30℃, the colony diameter of two strains increased with time. On the 8 th day, the colony diameter of the strains SCWJ-2 and GZGY-1-3 was 31-36 and 28-32 mm, respectively. On the 3 rd day, the colony diameter of strain SCWJ-2 was significantly larger than that of strain GZGY-1-3 under all test temperatures（P〈0.05）. The results of q RT-PCR showed that, with the exception of strain SCWJ-2 at 30℃, the gene copy number of both strains in F. occidentalis decreased on the 1 st day and gradually increased after 2 days at all the three temperatures. The gene copy number of strain SCWJ-2 within F. occidentalis was significantly higher than that of strain GZGY-1-3 under 30℃（P〈0.05）, but there was no significant difference between them under 25 and 20℃（P〉0.05）. 【Conclusion】 The number of fungal gene copies within insect host was affected by strains and temperatures, which is in accordance with the result of bioassay. Compared with B. bassiana strain GZGY-1-3, strain SCWJ-2 is more suitable for controlling F. occidentalis under high temperatures.