Source of mycorrhizal inoculum influences growth of Faidherbia albida seedlings

Poor land use management and practice inhibit the growth and establishment of tree seedlings in dryland areas.We assessed arbuscular mycorrhizal fungi(AM)status of Faidherbia albida(Del.)A.Chev.trees grown on different land uses.We quantified the growth and nutrient uptake of F.albida seedlings inoculated with AM from different sources.These efforts were based on soil and fine root samples from the rhizosphere soils of F.albida trees.AM root colonization was determined using the gridline intersect method.Spores were extracted by the wet sieving and decanting method and identified to genus level.The seedling experiment had a completely randomized onefactorial design with four treatments and five replications.Faidherbida albida seedlings were grown in a greenhouse.All in situ F.albida trees were colonized by AM fungi.AM root colonization of F.albida trees was significantly higher(P<0.0086)in area exclosures than on lands used for grazing or cultivation.Spore abundance was significantly higher(P<0.0014)in area exclosures followed by cultivated land and grazing land.Glomus was the dominant genus in all land-uses.AM-inoculated F.albida seedlings grew better(P<0.05)than non-inoculated controls.Seedlings inoculated with AM from area exclosure had significantly(P<0.05)higher growth and nutrient uptake than those inoculated with AM from grazing and cultivated land.This emphasizes the importance of the native soil AM potential for better establishment of seedlings to achieve optimum plant growth improvement and assist in rehabilitation of degraded arid lands.     

风化煤用量下覆膜和AM真菌对玉米生长和土壤微环境的影响

为缓解我国东部贫瘠土壤,以风化煤与覆膜为切入点,通过室内盆栽试验,研究两种覆膜方式(无覆膜和覆薄膜)和两个供试土壤基质(砂土基质和砂煤混合基质)下接种AM真菌对干旱胁迫时玉米生长特性、水分利用效率与土壤性状的影响。结果表明:两个覆膜方式下,砂煤混合基质相比砂土基质提高了接种AM真菌处理的玉米根系侵染率和土壤根外菌丝密度,但无明显差异;同时土壤总球囊霉素和易提取球囊霉素含量分别显著提高了80.0%~106.5%和55.0%~73.3%(P0.05)。同一覆膜方式下,砂煤混合基质接种AM真菌和CK处理的土壤有机碳、全氮与速效磷含量分别显著高于砂土基质下相应处理,但降低了土壤速效钾含量。砂煤混合基质下覆薄膜与接种AM真菌联合对玉米株高、生物量、叶片SPAD值及水分利用效率的促进效果最好;同时砂煤混合基质接种AM真菌处理提高了无覆膜下土壤蔗糖酶和全覆膜下过氧化氢酶和碱性磷酸酶含量,分别比砂土基质下处理显著提高了46.8%~59.8%、37.9%~70.0%与57.8%~87.5%(P0.05)。研究表明施加一定量风化煤时,接种AM真菌和覆薄膜能够促进水分胁迫下的植物生长发育,改善水分利用效率和提高土壤肥力。     

Colonization of Aeromonas salmonicida subsp. masoucida strains in Atlantic salmon (Salmo salar L.) during infection

Aeromonas salmonicida subsp. masoucida (ASM) is classified as atypical A. salmonicida and brought huge economic damages to the local salmonid aquaculture in China. An ASM strain named AS‐C4 was used to investigate the colonization of ASM in Atlantic salmon (Salmo salar L.) by an immersion challenge with the control group (T0, no AS‐C4), group T1 (2.67 × 10⁴ CFU/ml AS‐C4) and group T2 (2.67 × 10⁷ CFU/ml AS‐C4). The numbers of AS‐C4 copies in different fish tissues (gill, intestine, skin, blood, muscle, spleen, liver and kidney) were determined at different time points post challenge using the quantitative real‐time PCR (qRT‐PCR). AS‐C4 were detected in the gill and intestine as early as 0 hr after the challenge both in T1 and T2 groups, suggesting that the gill and intestine were probably the portals of entry of AS‐C4 into salmon. Although AS‐C4 could not be detected in the skin until 24 hr after the challenge in T1 group, it could be detected in the skin as early as 0 hr after the challenge in T2 group, indicating that the skin may also be a portal of entry of AS‐C4 into salmon. AS‐C4 was immediately detected in the blood within 3 hr after it entered the host, suggesting that AS‐C4 successfully invaded the bloodstream of fish. After AS‐C4 colonized the host, it colonized the internal tissues, such as the spleen, liver, kidney and muscle. The results of this study will contribute to the understanding of the pathogenesis of the ASM strains and give a broader understanding of the infection route of ASM in it's host, providing more information for the development of new therapeutic strategies to protect against this pathogen in aquaculture.     

根际微生物组构建的影响因素研究进展

基于根际微生物调控作物生长发育已成为生态健康和农业发展研究的热点。综述了国内外关于植物根际微生物组构建影响因素的相关研究进展,探讨了根际周边微生物从土壤进入植物根系内部的定殖选择过程,重点关注植物本体、土壤类型、地理位置、生长环境等因素对植物根际微生物组的调控作用,揭示国内外研究中发现的影响根际微生物组构建的主控因素,阐明根际微生物组-宿主复杂的互作关系,以期为绿色农业、环境生态保护等研究提供新的思路。     

群体感应信号物质对吡咯伯克霍尔德氏菌JK-SH007在杨树内定殖的影响

为了明确杨树溃疡病生防菌吡咯伯克霍尔德氏菌JK-SH007的群体感应系统是否与其内生定殖相关，本文通过群体感应指示菌紫色杆菌CV026和液相色谱串联四级杆飞行时间质谱技术（HPLC-Q-TOF-MS）确定其群体感应信号物质种类，并利用结晶紫染色、菌体回收、GFP标记等技术，研究其群体感应信号物质对该菌株生物膜及在杨树苗内的定殖能力的影响。结果表明，菌株JK-SH007产生的群体感应信号物质为含8个碳原子酰基侧链的辛酰基-L-高丝氨酸内酯（C₈-HSL）。群体感应信号物质C₈-HSL的添加对该菌株生物膜及在杨树苗内的定殖能力有影响，并且呈现低浓度促进，较高浓度抑制的规律。C₈-HSL的添加与菌株JK-SH007生物膜的OD值和菌体量具有显著相关性，相关系数分别为0.923和0.756。当添加1.0% C₈-HSL终浓度达到5×10^{-8 g/L}时，菌株JK-SH007生物膜的形成量达到峰值。荧光显微镜镜检发现，当添加100 μL C₈-HSL时，杨树组培苗根和茎中GFP荧光标记的菌株JK-SH007的定殖数量明显较CK多。菌株JK-SH007的群体感应与其在杨树内的内生定殖能力密切相关，群体感应信号物质C₈-HSL具有增强菌株JK-SH007内生定殖的能力，同时也表明该物质有利于该菌株生防效果的发挥。     

小麦赤霉病生防菌DZSG23的抗病机制

课题组前期从健康杜仲叶片中分离得到1株内生细菌枯草芽孢杆菌DZSG23,此菌可以较好地防控小麦赤霉病。为明确芽孢杆菌DZSG23在小麦中的定殖与强化抗病机制研究,利用抗生素标记法分析了DZSG23菌体在小麦组织中的定殖情况,采用荧光定量PCR技术检测不同生育期小麦穗部PR-1、AOS、ACOI等基因的表达水平变化。结果表明,DZSG23可在苗期小麦植株和小麦穗表面稳定定殖;DZSG23浇灌接种苗期小麦后的第34天,DZSG23在苗期小麦植株的根、茎和叶中的定殖量分别达到1.437×10⁶ CFU·g^-1、3.285×10³ CFU·g^-1和2.377×10³ CFU·g^-1;DZSG23喷施小麦穗表面15 d后,穗表面菌群密度仍可达7.146×10³ CFU·g^-1。此外,诱导系统抗性(ISR)信号通路研究表明,拮抗菌DZSG23可以诱导PR-1和AOS基因的上调表达,表明拮抗菌DZSG23引入小麦后可诱导小麦的水杨酸(SA)和茉莉酸(JA)信号通路,增强其抗病性。     

Arbuscular mycorrhizas and performance of Polylepis australis trees in relation to livestock density

Polylepis australis trees endemic to Argentina dominate the canopy of subtropical high altitude forests. Here, livestock rearing is the main economic activity and is suspect of the low performance of P. australis trees through direct and indirect effects which could include the reduction in arbuscular mycorrhizal fungi (AMF) and their benefit to trees. To elucidate the role of AMF, we compare plant performance indicators, arbuscular mycorrhizal (AM) colonization and AMF communities in 20 trees distributed in two areas of central Argentina which differed in livestock grazing intensity. The area with high livestock density presented more soil degradation and trees with a lower overall plant performance than the area with reduced livestock density. The AM colonization values of P. australis were considerably higher than reported for other tree species and the area with high livestock density had a lower proportion of arbuscules and higher proportion of hyphae, while vesicles and AM colonization – all structure considered together – did not differ between areas. Overall AMF spore number and of most species when considered separately was significantly higher in the area with high livestock density, suggesting a high tolerance and adaptation of AMF to livestock. We conclude that a reduction in livestock improves the performance of P. australis, that this improvement could be mediated by an increase in the proportion of arbuscules, but there does not appear to be any limitation in AM colonization or AMF spore number which could otherwise be limiting forest restoration.     

Functional compatibility of two arbuscular mycorrhizae with thirteen fruit trees in Senegal

Functional compatibility between thirteen tropical fruit trees (Afzelia africana Smith., Adansonia digitata L., Aphania senegalensis Radlk., Anacardium occidentale L., Cordyla pinnata (Lepr. ex A. Rich.) Milne-Redhead, Dialium guineensis Wild., Landolphia heudelottii A.DC., Sclerocarya birrea (A.Roch.) Hochst., Saba senegalensis (A. DC.) Pichon and four reference hosts Balanites aegyptiaca (L.) Del., Parkia biglobosa (Jacq.), Tamarindus indica L. and Zizyphus mauritiana Lam.) and two arbuscular mycorrhizal fungi (AMF) (Glomus aggregatum Schenck and Smith emend. Schenck and Glomus intraradices Schenck and Smith), was investigated. Marked differences were found between them in terms of mycorrhizal formation, root colonization, relative mycorrhizal dependency (RMD) and phosphorus concentrations in shoot tissues. A. africana, L. heudelottii and S. senegalensis did not form symbiotic associations, and the growth of A. africana decreased following mycorrhizal inoculation, while L. heudelottii and S. senegalensis showed no dependency. In contrast, A. digitata, A. senegalensis, A. occidentale, B. aegyptiaca and S. birrea were well colonized with AMF, but did not significantly increase in biomass production. Five fruit trees did, however, show dependency by a positive interaction with G. aggregatum, the most effective AMF. Z. mauritiana was found to be very highly dependent (RMD > 75%), T. indica was highly dependent (50–75% RMD), and D. guineensis, P. biglobosa and C. pinnata were moderately dependent (25–50% RMD). Phosphorus absorption probably contributed to this dependency more than the absorption of potassium. These results indicate that some tropical fruit trees do derive benefits from AM inoculation, while others do not.This revised version was published online in November 2005 with corrections to the Cover Date.     

水稻内生细菌B196的鉴定及其对水稻纹枯病的防治作用

从水稻体内分离得到的细菌菌株B196对水稻纹枯病菌Rhizoctonia solani的生长有较强抑制作用.通过形态学和生理生化鉴定及16S rDNA序列分析,将菌株B196鉴定为巨大芽孢杆菌Bacillus megaterium.采用浸种和喷雾的方法将菌株B196接种到水稻植株后,均能在稻株体内回收到该菌株,表明菌株B196能在水稻体内定殖.菌株B196对水稻纹枯病的盆栽和田间防效分别为64.29%和55.13%.