松材线虫侵染的马尾松人工林细根形态及生物量分异特征

中龄林的马尾松受松材线虫侵染后,林木生长、生理生化指标、群落多样性等会发生异质性变化,但是,针对患病林木地下细根的响应尚不清楚。本研究以松材线虫疫区患病马尾松和健康马尾松为研究对象,采用土柱法,分0-15 cm和15-30 cm土层,对细根进行分级研究,定量分析1-5级细根的形态、生物量以及养分元素,探讨松材线虫侵染的马尾松人工林细根形态、生物量以及养分元素的分异特征。结果表明:(1)患病马尾松人工林细根的健康状态与根长密度、生物量呈极显著正相关(P<0.01),低级根(如1级根)患病后,响应会更加强烈。(2)马尾松人工林患病后,细根有效磷、速效钾浓度会显著降低(P<0.05),而全氮、钙浓度会显著升高(P<0.05)。(3)松材线虫病使林分的土壤有机质含量显著高于健康林分(P<0.05),而土壤速效钾含量会显著低于健康林分(P<0.05)。以上结果表明,松材线虫侵染的马尾松人工林会在细根形态、细根养分和土壤养分上会发生特异性响应,揭示了松材线虫病对马尾松人工林地下细根的影响,旨在为松材线虫病防治提供一定参考。     

云南省烟植地青枯菌RS-22的分离及其拮抗菌的筛选和鉴定

【背景】由青枯劳尔氏菌(Ralstonia solanacearum)引起的烟草青枯病是一种重要土传病害,在我国南方烟区普遍发生。生物防控是针对烟草青枯病的一种有效防治措施,但是相关的研究报道还较少。【目的】分离云南省烟植地的青枯病原菌,筛选其拮抗菌并对其抑菌效果进行鉴定。【方法】采用平板稀释法从云南感病烟草中分离获得青枯菌,采用平板对峙法筛选青枯菌拮抗菌,筛选得到的拮抗菌通过16SrRNA基因测序比对确定菌种类型,并在实验室和大田鉴定其对青枯病的防治效果。【结果】从感病烟草茎中分离出一株强致病性青枯菌小种RS-22,该菌能侵染烟草和番茄并最终使植物死亡;筛选出12株RS-22拮抗菌,其中拮抗作用最强的是Y4;Y4被鉴定为一株解淀粉芽孢杆菌(Bacillus amyloliquefaciens),其菌体和分泌物都能抑制RS-22生长;Y4根部灌根处理能显著提高烟草和番茄对青枯菌RS-22的抗性,Y4处理能使感病烟草部分恢复正常,在云南文山州烟草种植大田施加Y4菌剂和菌剂有机肥混合物也能显著降低烟草青枯病的感病率。【结论】青枯菌RS-22具有广谱的致病性,筛选的拮抗菌Y4能显著抑制青枯菌生长,而且对青枯菌侵染植物有很好的防治效果。研究结果为进一步研究烟草青枯病的生物防控提供了新的理论依据。     

尖孢镰孢菌果胶裂解酶基因家族鉴定及侵染表达模式分析

【背景】番茄枯萎病是番茄生产中常见的土传真菌病害。【目的】为鉴定番茄枯萎病基因组果胶裂解酶基因家族,明确该基因家族在侵染过程表达模式。【方法】采用生物信息学方法鉴定了番茄枯萎病尖孢镰孢菌(Fusarium oxysporum f. sp. Lycopersici)基因组内PEL基因家族,并分析了基因结构、染色体定位及三级结构,同时利用荧光定量PCR分析了FoPEL1-16基因在接种番茄根系的表达情况。【结果】番茄尖孢镰孢菌基因组内PEL基因家族成员有16个。氨基酸序列长度在163-548个氨基酸,信号肽长度在16-21个氨基酸。染色体定位分析表明16个基因在染色体上分布不均,分别定位在7条染色体上。根据基因结构和保守基序分析结果 16个基因可分为4类。进化分析表明该基因家族成员可聚成4支。三级结构预测结果显示同一家族存在相似结构域。荧光定量PCR分析结果表明Fo PEL基因在侵染过程表达水平明显上升。【结论】番茄尖孢镰孢菌基因组内果胶裂解酶以基因家族形式存在,其基因结构存在差异暗示了其功能多样性;FoPEL基因在侵染过程表达明显增强,说明其参与病原菌的致病性。本研究为解析尖孢镰孢菌致病基因功能分析及寄主病原互作提供了重要理论基础。     

米修链霉菌TF78对香蕉枯萎病的田间防效及根际土壤微生物的影响

【背景】香蕉枯萎病是香蕉生产上的毁灭性病害,生物防治是遏制该病害发生的有效手段。在前期的研究中,从健康香蕉根际土壤中分离获得一株对香蕉枯萎病具有良好盆栽防治效果的生防菌——米修链霉菌(Streptomyces misionensis) TF78,但其对香蕉枯萎病的田间生防潜力和对土壤微生物环境的影响尚不清楚。【目的】评价米修链霉菌TF78对香蕉枯萎病的田间防治效果,明确其对香蕉根际土壤微生物群落的影响。【方法】选取两块发病香蕉园,测定该生防菌株对香蕉枯萎病的防治效果,并利用扩增子测序技术分析施用菌剂组和空白对照组共12份香蕉根际土壤的微生物多样性和丰度。【结果】米修链霉菌TF78对两块香蕉园的田间防效分别达55.30%和45.32%。该生防菌株处理组的物种稀释曲线坡度大于空白对照组,并显著富集了优势种群梳霉门(Kickxellomycota),消减了绿弯菌门(Chloroflexi)、酸杆菌门(Acidobacteria)和苔藓杆菌(Bryobacter)的丰度,对土壤中优势种群变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)、芽单胞菌门(Gemmatimonadetes)及木霉属(Trichoderma)、鞘氨醇单胞菌属(Sphingomonas)、寡养单胞菌属(Stenotrophomonas)和芽孢杆菌属(Bacillus)的相对丰度影响不显著。【结论】米修链霉菌TF78塑造了不利于香蕉枯萎病菌Fusarium oxysporum f.sp.cubense存活的土壤环境,有效降低了田间香蕉枯萎病的发生,同时对土壤中大部分具有重要生态功能和抑菌功能的优势微生物种群影响不显著。该研究结果为米修链霉菌TF78的进一步开发应用奠定了基础。     

In vitro and greenhouse evaluations of Trichoderma isolates for biological control of potato wilt disease (Fusarium solani)

The biological efficacy of Trichoderma species may differ due to variations in ecosystems. This study was conducted to assess the biocontrol efficacy of some native Trichoderma isolates against Fusarium solani, an important causal agent of potato wilt disease under laboratory and greenhouse conditions at Shahrood Agricultural Research Centre, Shahrood, Iran, during 2006–2007. Fourteen isolates were collected among which eight showed promising ability in inhibiting the growth of the pathogen through dual culture and production of volatile and non-volatile inhibitors but T. brevicompactum (T1), T. longibrachiatum (T5) and T. asperellum (T2) were almost better than other isolates in inhibiting the mycelial growth of the pathogen in comparison to control in the above three tests (p ≤ 0.01). Isolates performing mycoparasitism under in vitro condition were evaluated against the disease in pot culture under greenhouse condition. In all treatments in which Trichoderma isolates + F. solani were involved lower disease incidence was noticed in comparison to Fusarium-infested control (p ≤ 0.05). Best disease control was observed in potted plants treated with F. solani + T. longibrachiatum (T5) with 6.25% disease incidence in comparison to Fusarium-infested control, in which disease incidence was observed to be 75%. Interaction of T. brevicompactum (T1) and F. solani also indicated good control of the disease by 12.50% of disease incidence.     

Quantitative assessment of the interaction between the antagonistic fungus Talaromyces flavus and the wilt pathogen Verticillium dahliae on eggplant roots

Quantitative aspects of the interaction between the antagonist Talaromyces flavus, the pathogen Verticillium dahliae and eggplant roots, were studied. When eggplant roots were inoculated with T. flavus, prior to the infection with the pathogen, the population density of T. flavus on V. dahliae-infected roots was at least 3 times higher than on healthy uninfected roots, and the proliferation of T. flavus on diseased eggplant roots was related to the severity of wilt symptoms, in the two levels of application of T. flavus studied. However, in all classes of disease severity tested (disease index, 0–3), the population density of T. Flavus on eggplant roots treated with 10⁶ ascospores g^–1 rooting mixture was significantly (p=0.05) higher than with 10⁵ ascospores g^–1. In roots treated with 10⁵ and 10⁶ T. flavus ascospores g^–1 rooting mixture, the population density of V. dahliae was reduced by 51% and 69%, respectively. When testing the relationships between the population density of V. dahliae in the roots and disease severity, no significant (p=0.05) difference was found between disease indexes 2 and 3. However, the density of V. dahliae on roots of plants with disease index 1 was significantly (p=0.05) lower than disease indexes 2 and 3. The positive relationship between the inoculum concentration of V. dahliae and the population density of T. flavus developed on eggplant roots was significant (p=0.001), linear, and highly correlated (r=0.945) on a logarithmic scale. In addition, the analysis of these data revealed a significant (p=0.05), high, negative and linear correlation (r=–0.985) between the log concentration of V. dahliae inoculum and the disease reduction achieved by T. flavus.     

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

Nemtaode-Vector Relationships in the Pine Wilt Disease System

Pinewood nematode, Bursaphelenchus xylophilus, is the causal agent of pine wilt disease in North America and Japan. Dispersal stage dauer larvae are transported to new host trees on the body surface and within the tracheal system of several beetle species. Worldwide, 21 species of Cerambycidae, 1 genus of Buprestidae, and 2 species of Curculionidae are known to carry pinewood nematode dauer larvae upon emerging from nematode-infested trees. Five species of cerambycids in the genus Monochamus are known to transmit dauer larvae to new host trees, four North American species and one Japanese species. Primary transmission to healthy trees occurs through beetle feeding wounds on young branches. Secondary transmission to stressed trees or recently cut logs occurs through Monochamus oviposition sites.     

Effect of Simulated Acid Rain on Bursaphelenchus xylophilus Infection of Pine Seedlings

White, Scots, and Austrian 3-year-old pine seedlings were treated with conditions simulating acid rain and inoculated with the white pine specific pathotype of Bursaphelenchus xylophilus, VPSt-1. Oleoresin concentration increased slightly and carbohydrate concentration decreased in all seedlings treated with simulated acid rain (SAR). The changes were significantly increased after inoculation of SAR-treated white and Scots pine seedlings with VPSt-1. Wilting was delayed and nematode reproduction decreased in SAR-treated white pine seedlings inoculated with VPSt-1. SAR-treated Austrian pine seedlings were resistant to VPSt-1, but SAR-treated Scots pine seedlings lost tolerance to VPSt-1 and wilted 50-60 days after inoculation.     

Biological control ofFusarium oxysporum f.sp.cubense in banana by inoculation withPseudomonas fluorescens

Native strains ofPseudomonas fluorescens exhibitedin vitro antibiosis towards isolates of races 1 and 4 ofFusarium oxysporum f.sp.cubense, the Panama wilt pathogen of banana. The seedlings ofMusa balbisiana seedlings treated withP. fluorescens showed less severe wilting and internal discolouration due toF. oxysporum f.sp.cubense infection in greenhouse experiments. In addition to suppressing Panama wilt, bacterized seedlings ofM. balbisiana also showed better root growth and enhanced plant height.