不同生长条件下球孢白僵菌菌株的生长状况及对美国白蛾幼虫的致病力研究

试验所用球孢白僵菌（Beauveria bassiana）是从受侵染的美国白蛾[Hyphantria Cunea（Drury）]蛹体内分离出的菌株,再进行纯化,获得球孢白僵菌纯菌落。研究测定了不同生长条件对球孢白僵菌菌株的营养生长、孢子萌发以及对不同龄期美国白蛾幼虫致病力的影响。结果表明：相对湿度为90%时,菌株的营养生长最好,随着相对湿度的增大,孢子萌发速度、萌发率也增高;相对湿度为100%时孢子萌发率达到最高。经紫外线照射后菌株的营养生长速度缓慢,孢子萌发率降低。相对湿度为90%时被该菌株感染的美国白蛾幼虫的死亡率最高,3龄幼虫的死亡率比6龄幼虫高。     

球孢白僵菌BbO6菌株对亚洲玉米螟的药效试验

通过球孢白僵菌孢子悬浊液感染幼虫的方法检测球孢白僵菌BbO6菌株对玉米螟的毒力和防治效果,旨在探讨玉米螟无公害的防治方法.室内浓度为109、1010、1011 cfu/L的孢子悬浮液感染玉米螟幼虫,死亡率分别为59.8%、78.2%、92.0%,LT50值分别为8.1、5.9、4.9 d,处理后10 d的LC50值为8.1×108 cfu/L.在田间,浓度为1011cfu/L的悬浮液喷药后10、60 d的防效分别为57.7%和73.6%,蛀孔减退率达77.7%.结果表明该菌株对玉米螟具有较强的致病性,可使玉米的产量和质量大幅度提高.     

He–Ne激光对球孢白僵菌生物学特性的影响

应用He-Ne激光对球孢白僵菌Beauveria bassiana 75A进行辐照处理. 研究了不同剂量激光辐照对菌体生长的影响，辐照强度0.48 mW/cm2、辐照15 min利于菌体的诱变. 两种激光辐照方式中，生理盐水菌悬液辐照方式诱变效果较好. 经发酵产孢实验和菌体生物量测定，发现He-Ne激光对球孢白僵菌具有明显的生物刺激效应和诱变作用，并初步筛选到产孢量有较大变化的辐照变异菌株；同时，通过对变异菌株的细胞外、胞周间、细胞内三位区的RNA和DNA分析，进一步证实了He-Ne激光对球孢白僵菌的诱变作用.     

球孢白僵菌Bb080920菌株对番石榴实蝇的毒力测定

[目的]筛选出防治番石榴实蝇Beauveria bassiana(Bezzi)的有效生防菌。[方法]分别采用喷雾法和浸渍法测定不同浓度的球孢白僵菌Bb080920分生孢子液对番石榴实蝇成虫、幼虫和蛹的室内毒力。[结果]成虫的最大校正死亡率达(91.83±2.42)%,致死中浓度(LC50值)为(2.6281±0.2362)×108个/L,致死中时间(LT50值)为(4.61±0.37)d;幼虫最大累计校正死亡率达(95.23±3.13)%,LC50值为(2.5416±0.8395)×108个/L,LT50值为(4.36±0.42)d;蛹的累计校正死亡率最大达(82.59±2.78)%,LC50值为(2.7692±0.1538)×108个/L,LT50值为(5.05±0.68)d。[结论]球孢白僵菌Bb080920菌株毒力测定表明具有很高的毒性,未来有良好的应用前景。     

6种常用农药与球孢白僵菌和蜡蚧轮枝菌的相容性

测定了3种杀虫剂和3种杀菌剂在田间常规浓度下对球孢白僵菌和蜡蚧轮枝菌孢子萌发和菌丝生长的影响。供试杀虫剂对球孢白僵菌孢子萌发的影响很小,萌发率超过85％,对蜡蚧轮枝菌孢子萌发影响较大,抑制作用最小的吡虫啉,抑制率达到25％。3种杀菌剂几乎完全抑制了孢子的萌发。杀虫剂对球孢白僵菌的菌丝生长有一定抑制作用,抑制率为22．60％-38．39％;对蜡蚧轮枝菌菌丝生长的影响小于对球孢白僵菌的影响,抑制率为10．06％．17．61％。供试杀菌剂对球孢向僵菌和蜡蚧轮枝菌菌丝生长的抑制作用都较大,抑制率都在50％以上。     

球孢白僵菌Snf907发酵液对番茄根结线虫病的控病效果及防御酶活性影响

研究球孢白僵菌Snf907不同浓度发酵液对番茄幼苗期南方根结线虫病(Meloidogyne incognita)的室内防效,并测得处理后番茄幼苗根内几种主要寄主防御反应酶系PAL、POD、PPO、SOD和可溶性蛋白PRO活性的动态变化.结果表明:不同浓度的发酵液对根结和卵囊的抑制率均明显高于对照,其中原液和5倍稀释液达到80%以上.不同浓度发酵液处理后番茄幼苗根部的PAL、POD、PPO、SOD活性均高于对照,PRO活性显著增加.显示了球孢白僵菌在促进植物生长方面的潜能.     

球孢白僵菌与印楝素复配对草地螟的增效作用

测定了不同配比的球孢白僵菌(Beauveria bassiana)菌株S3与印楝素对草地螟(Loxostege stfcticalis L.)幼虫致病率的增效作用。通过数学模型对复配剂的共毒系数与复配剂中单剂的比例关系进行拟合,获得了最佳理论配比。测试结果表明,白僵菌菌株与印楝素在1:10、1:4、1:2、1:1和5:2配比作用下对草地螟幼虫都有增效作片用,7×10~7孢子/mL白僵菌菌株S3与14 mg/mI。印楝素的最佳理论配比为3 978:l,此时混剂对草地螟幼虫具有最大的共毒系数333.608 3。田间试验亦证明混用能提高药效,具有较显著的增效作用。     

侵染马铃薯块茎蛾幼虫的球孢白僵菌对桃蚜的毒力测定

室内测定了从罹病马铃薯块茎蛾Phthorimaea operculella(Zeller)幼虫上分离到的球孢白僵菌Beauveris bassiana两菌株(Bb001，Bb004)对甘蓝桃蚜Myzus persicae(Sulzer)的毒力。运用时间-剂量-死亡率模型，对死亡率随时间和剂量的变化趋势，以及两种菌株在不同温度下对桃蚜的毒力作了分析。结果表明：两种菌株对桃蚜均具有毒杀作用，菌株Bb004在21℃下表现了较高的毒力，菌株Bb001在21℃～28℃下对桃蚜均有较强的致病力，2l℃～25℃下是两菌株共同发挥毒力最佳的温度。其中，Bb001有较宽的适宜温度范围，而Bb004适宜温度范围较小。     

球孢白僵菌基于前体物固态发酵合成D-HPPA

[目的]建立球孢白僵菌(Beauveria bassiana)基于前体物固态发酵合成R-(+)-2-(4-羟基苯氧基)丙酸(D-HPPA)的工艺,提高球孢白僵菌催化R-(+)-2-苯氧基丙酸(D-PPA)合成D-HPPA的能力。[方法]对前体物(D-PPA)添加量及添加时机进行了探索,同时对影响固态发酵的因素如固态基质种类、料水比、培养基水分pH、接种量及发酵温度等进行了优化。[结果]前体物添加量低于30 g D-PPA/kg固态培养基时,球孢白僵菌能够在7 d内完成D-PPA的转化,且在固态发酵起始阶段即可加入前体物进行催化。以麸皮为固态培养基基质,培养基料水比为1∶1.5、初始水分pH为7.5、接种量15%,培养温度为26℃时球孢白僵菌的催化效率最高。在40 g/kg的前体物存在下发酵7 d,D-HPPA产量达到37.34 g/kg,前体物D-PPA转化率为93.35%,较液态发酵方式的转化率提高283.38%。[结论]球孢白僵菌基于前体物固态发酵能够有效合成D-HPPA,为其生物合成提供了一条新的途径。     

球孢白僵菌催化合成R-(+)-2-(4-羟基苯氧基)丙酸的菌种选育

[目的]为采用生物转化法合成R-(+)-2-(4-羟基苯氧基)丙酸(D-HPPA)提供优良菌株及理论基础。[方法]针对球孢白僵菌,先采用紫外(UV)诱变筛选高耐受R-(+)-2-苯氧基丙酸(D-PPA)的突变株,再使用等离子体(ARTP)诱变、N-甲基-N′-硝基-N-亚硝基胍(MNNG)诱变及ARTP和MNNG复合诱变提高突变株底物转化率。[结果]得到突变株UA1052,其底物转化率为98.5%、平均每天产物积累速率为6.93 g/(L·d)(较出发菌提高了796.6%),且遗传性稳定。[结论]ARTP诱变可大幅提高球孢白僵菌催化合成D-HPPA的能力。     

Low-Temperature Spray Drying for the Microencapsulation of the Fungus Beauveria bassiana

Low-temperature spray drying was used to microencapsulate the conidia of Beauveria bassiana. In order to prolong the activity of the conidia and improve their shelf life, various polymers (including hydroxypropyl methyl cellulose [HPMC], chitosan, dextrin, skimmed milk, and polyvinylpyrrolidone [PVP K90]) were examined as encapsulation matrices. Different inlet/outlet temperatures, compositions of the carrier systems, and conidia concentrations were examined with respect to spore viability. Moreover, the production characteristics, such as particle size distribution, entrapment efficiency, and shape, were investigated. The best encapsulated products were obtained using a matrix composed of 10% dextrin, 10% skimmed milk, and 5% PVP K90 as the coating material. The conidia exhibited 80% viability, even after storage for 6 months at 4°C. The microspheres obtained by spray drying were spherical with smooth or wrinkled surfaces. The mean particle size was in the range of 2.5–10 μm. The yield (%) using dextrin/SM/PVP K90 as coating material having maximum viability was 68 ± 4, whereas that with dextrin only as coating material was 85 ± 3.     

Biosynthesis of the 2-pyridone tenellin in the insect pathogenic fungus Beauveria bassiana

Genomic DNA from the insect pathogenic fungus Beauveria bassiana was used as a template in a PCR with degenerate primers designed to amplify a fragment of a C-methyl transferase (CMeT) domain from a highly reduced fungal polyketide synthase (PKS). The resulting 270-bp PCR product was homologous to other fungal PKS CMeT domains and was used as a probe to isolate a 7.3-kb fragment of genomic DNA from a BamH1 library. Further library probing and TAIL-PCR then gave a 21.9-kb contig that encoded a 12.9-kb fused type I PKS-NRPS ORF together with ORFs encoding other oxidative and reductive enzymes. A directed knockout experiment with a BaR cassette, reported for the first time in B. bassiana, identified the PKS-NRPS as being involved in the biosynthesis of the 2-pyridone tenellin. Other fungal PKS-NRPS genes are known to be involved in the formation of tetramic acids in fungi, and it thus appears likely that related compounds are precursors of 2-pyridones in fungi. B. bassiana tenellin KO and WT strains proved to be equally pathogenic towards insect larvae; this indicated that tenellin is not involved in insect pathogenesis.     

Sodium Humate as a Promising Coating Material for Microencapsulation of Beauveria bassiana Conidia Through Spray Drying

Microencapsulation of Beauveria bassiana (Bb) conidia with sodium humate (SH) was undertaken successfully through spray drying at a high inlet air temperature of 175°C with corresponding outlet air temperature of 86.5 ± 1.3°C using 0.2% SH. The obtained product was a free-flowing, dark-brown powder containing microcapsules of Bb conidia coated with sodium humate (Bb-SH). These microcapsules measured 2.47–3.57 µm and possessed an uneven, fluffy surface. The colony-forming units (CFU) of Bb-SH microcapsules spray-dried at 175°C were 21.54 LCFUg^?1, on par with 21.59 LCFUg^?1 for Bb conidial powder not subjected to spray drying. Bb-SH microcapsules resulted in a high mortality of 93.0% against six-day-old Helicoverpa armigera larvae within five days after treatment. Bb-SH microcapsules readily dispersed in water, releasing sodium humate from the conidial surface. Germination of conidia was not affected by sodium humate as visualized by scanning electron microscopy of the cuticular surface of treated larvae. Bb-SH microcapsules showed good viability (21.11 LCFUg^?1) at the end of six months of storage at room temperature (～30°). Thus, sodium humate is a promising biopolymer for encapsulation of Bb conidia for extended shelf-life at room temperature.