Time and burial depth influencing the viability and bacterial colonization of sclerotia of Sclerotinia sclerotiorum

Sclerotia are the primary over wintering inoculum of Sclerotinia sclerotiorum (Lib.) de Bary. The effects of tillage on the primary inoculum are not well understood. The purpose of this research was to study sclerotial viability over time and between burial depths in soil, to identify bacteria colonizing and degrading the sclerotia, and determine whether these bacteria may be utilized as biological control agents. Correlation analysis indicated that a significant negative relationship existed between sclerotial viability and elapsed temporal factors (R²=−0.68, P<0.0001), and depth of burial (R²=−0.58, P<0.0001). After twelve months, sclerotia on the soil surface had the highest viability (57.5%), followed by those at the 5 cm depth (12.5%), and only 2.5% of those placed at the 10 cm depth remained viable. A significant negative relationship between sclerotial viability and bacterial populations also existed (R²=−0.60, P<0.0001). Two hundred and sixty-eight bacteria were isolated from sclerotia, 29 of which showed strong in vitro antagonism to the mycelial growth of S. sclerotiorum. Biodiversity of the inhibitory bacterial isolates was minimal on sclerotia from the soil surface and within all depths sampled at three months (i.e. in January). All burial depths within the April and July sampling dates produced bacterial diversities that were distinct from each other.     

Survival of Coniothyrium minitans associated with sclerotia of Sclerotinia sclerotiorum in soil

The development and survival of the mycoparasite Coniothyrium minitans associated with sclerotia of the plant pathogen Sclerotinia sclerotiorum was studied in pasteurised and non-sterile (untreated) soil. Using scanning electron microscopy, developing pycnidia were first seen within the sclerotial medulla at 7 days post-inoculation with the mycoparasite in pasteurised soil. However, by 14 days post-inoculation, pycnidia had developed fully in both pasteurised and non-pasteurised treatments, and conidial droplets were exuded onto the outer surface of the infected sclerotia. Thirty days post-inoculation, irrespective of soil treatment, the majority of the sclerotial medulla had been converted to pycnidia, with the sclerotial rind remaining largely intact. The pycnidia and dried intact droplets were still observed 6 months post-inoculation with C. minitans, although the conidia on the outer surface of the dried droplets had largely collapsed by this stage. Germinability studies at 10 months post-inoculation showed that approximately 13% of the conidia in dried droplets were still viable. This work shows the potential for infected sclerotia of S. sclerotiorum to provide a unique reservoir for the survival of C. minitans.     

Relationship between the biocontrol fungus Trichoderma harzianum and the phytopathogenic fungus Fusarium solani f.sp. pisi

Relationship between the biocontrol fungus Trichoderma harzianum ThzID1-M3 and the plant pathogen Fusarium solani f.sp. pisi (Fsp) was determined in this study. Dual culture assay indicated the competitive interaction between ThzID1-M3 and Fsp. Alginate pellets of ThzID1-M3 and Fsp conidia were added to non-sterile soil with pea seeds. The interaction between Trichoderma and Fsp adversely affected their establishment in soil. The addition of ThzID1-M3 significantly reduced the Fsp population, as well as the colonization of roots by Fsp. In contrast, the added Fsp significantly reduced the proliferation of ThzID1-M3 and Trichoderma spp. The results suggest that the competition may be the main mechanism of the antagonistic activity of Trichoderma against Fsp.     

土壤不同微生物量对木霉菌定殖的影响和木霉菌生态学习性研究

木霉菌（Trichodermaspp．）在真菌中具有重要生防价值，以其存在的广泛性、在环境中易定殖、繁殖速度快等优点受到人们的重视。20世纪70年代以来人们对生防机制作了深入研究，证实木霉菌对植物病原真菌具有竞争作用、重寄生作用、抗生作用、诱导植物抗病性等生防机制，并从分子水平上探索了其作用机理。同时人们以木霉菌活菌为材料对多种植物病害的防病效果进行了大量小型试验，取得了较好效果，并以此为基础研制出了木霉菌生防农药。但在生产实践中发现，木霉菌活菌制剂的田间应用效果与实验室的试验效果相差甚远。笔者认为木霉菌在自然环境中的定殖与繁殖不仅受到温度、湿度等物理环境因素的影响，同时也会受到环境中其他微生物的影响，以往的研究多集中在物理因素方面，本试验研究了木霉菌在不同微生物量土壤中的定殖情况及木霉菌生态学习性，旨在为生产实践中提高木霉菌的生防效果提供依据。     

Evaluation of different Coniothyrium minitans inoculum sources and application rates on apothecial production and infection of Sclerotinia sclerotiorum sclerotia

The effects of three Coniothyrium minitans isolates (Conio, IVT1 and Contans^®), applied to soil as conidial suspensions or as maizemeal-perlite (MP) inocula (Conio), on apothecial production and infection of Sclerotinia sclerotiorum sclerotia were assessed in two soil pot bioassays and two novel box bioassays in the glasshouse at different times of the year. C. minitans isolate Conio applied as either MP or ground MP at full rate (10⁶-10⁷ cfu cm⁻³ soil) consistently decreased the carpogenic germination, recovery and viability of sclerotia and increased C. minitans infection of the sclerotia of S. sclerotiorum by in comparison with either MP or conidial suspension treatments applied at lower rates (10³-10⁴ cfu cm⁻³ soil). Additionally, when applied at the same rate, MP inoculum of C. minitans was consistently more effective at reducing carpogenic germination than a conidial suspension. The effect of MP and ground MP at full rate on carpogenic germination was expressed relatively early as those sclerotia recovered before apothecia appeared on the soil surface already had reduced numbers of apothecial initials. In general, there were few differences between the isolates of C. minitans applied as conidial suspensions. Box bioassays carried out at different times of the year indicated that temperature and soil moisture influenced both apothecial production and mycoparasitism. Inoculum concentration of C. minitans and time of application appear to be important factors in reducting apothecial production by S. sclerotiorum.     

利用微生物防除根寄生杂草列当

根寄生杂草列当(Orobanche spp.)已经严重制约全球许多地区的农业发展,寻找有效防除措施迫在眉睫。由于列当具有特殊生活史且与寄主关系密切,常规防除杂草措施难以达到理想防效。目前,尚无既能有效防除列当又不对寄主造成危害且便于大规模推广应用的列当防除措施。在众多列当防除措施中,微生物防除越来越引起关注和重视。本文对微生物防除列当的国内外研究进展及防除机理进行了综述。目前,列当生防微生物的研究主要集中在镰刀菌(Fusarium spp.)等列当病原菌和根瘤菌(Rhizobium spp.)等列当寄主植物共生菌上。微生物防除列当的机制主要包括两方面:一是通过产生代谢产物直接影响列当的萌发和生长,或通过降解列当种子萌发诱导物质间接影响列当的萌发;二是通过提高寄主植物自身对列当的抗性间接影响列当的寄生和生长。此外,本文还重点介绍了植物土传病害的土壤拮抗微生物防除列当杂草的可行性及研究进展。植物土传病害病原菌和列当均首先通过在地下侵染作物的根系进而危害作物正常生长,而作物抗土传病害的机理也与抗列当的机理类似。因此,存在于土壤中具有防治植物土传病害能力的微生物可能也具有防除根寄生杂草列当的功能。本团队前期试验从植物土传病害的土壤拮抗微生物中筛选到在盆栽试验中能够有效防除向日葵列当(O.cumana Wallr.)和瓜列当(O.aegyptiaca Pers.)的放线菌各1株,分别为淡紫褐链霉菌(Streptomyces enissocaesilis Sveshnikova)和密旋链霉菌(Streptomyces pactum Bhuyan B.K)。其中,密旋链霉菌的菌剂在田间试验中既降低了瓜列当的出土数量又增加了番茄的产量。总之,微生物是防除根寄生杂草列当的一条有效途径。     

Pyruvate dehydrogenase activity is important for colonization of seeds and roots by Enterobacter cloacae

Enterobacter cloacae is a plant-beneficial bacterium that shows promise for suppression of damping-off of cucumber and other crops caused by Pythium ultimum. We have been using a mutational approach to determine the E. cloacae genes important in bacterial-plant and bacterial-pathogen interactions in the spermosphere and rhizosphere. E. cloacae M43 is a transposon mutant of E. cloacae 501R3 that was significantly impaired in colonization of seeds and roots of diverse crop plants. Strain M43 did not increase in population on cucumber, sunflower, and wheat seeds and was significantly reduced in growth on pea seeds relative to strain 501R3. Populations of M43 were also dramatically lower than those of strain 501R3 in cucumber, pea, sunflower, and wheat rhizosphere in 42 d experiments. Molecular characterization of M43 demonstrated that there was a single transposon insertion in the genome of this strain and that this insertion was in a region of the E. cloacae genome with a high degree of DNA sequence identity with aceF. aceF encodes the dihydrolipoamide acetyltransferase subunit of the pyruvate dehydrogenase complex (PDHC). Cell lysates from strain 501R3 grown on minimal medium plus 50 mM glycerol and 2 mM acetate contained 0.011±0.0036 U pyruvate dehydrogenase activity while cell lysates from M43 grown under identical conditions contained no detectable pyruvate dehydrogenase activity. Additionally, the nutritional use profile of M43 under aerobic and anaerobic conditions was as expected for an ace mutant. Experiments reported here strongly suggest a role for aceF and the PDHC in colonization of seeds and roots of diverse crop plants by E. cloacae.     

苋菜对钾素吸收和利用上的基因型差异

The kinetics of K^ absorption and the utilization of both applied K and K in a calcareous alluvisol with low available K by different genotypes of grain amaranth(Amaranthus spp.),an ancient pseudo-cereal that produces a large biomass and a rich source of health nutrients and mineral elements,were studied by means of ion depletion technique and pot experiments.Grain amaranth had a high affinity for K^ absorption comparison with corn and cotton.However,there were differences among Amaranthus spp.in Kabsorption and utilization.Some cultivars such as R104,CX-4,Du001,Hy015 and Hr029 which had a higher rate of K absorption and stronger affinity for K^ were typical varieties with high K-use efficiency(KUE).The results showed that high KUE cultivars grew quickly,possessed stronger ability to take up soil slowly available K and Mineral K,and did not respond to K fertilization in the soil with low available K.Correspondingly,grain amaranth cultivars CX-77,Cr024,Vd001,Re003 and Sn003 were relatively low in KUE,Compared with high KUE cultivars,they took up more soil available K and both of their dry matter accumulation and K uptake responded to K applied significalty.     

Incidence of eyespot on winter triticale and quantification of Oculimacula spp. population using real-time PCR in Lithuania

The aim of this study was to estimate the incidence of eyespot in winter triticale crops in different agro-ecological zones of Lithuania and to use real-time polymerase chain reaction (Real-time PCR) to determine the dominant Oculimacula fungi populations in winter triticale crops grown in Lithuania, which has not been previously established. Differences in common fungicide usage practices in triticale crops between Lithuanian agro-ecological zones suggest that the composition of Oculimacula fungi differs across the country. From 2008 to 2012, a total of 70 winter triticale fields were reviewed for eyespot incidence, and the presence of eyespot was identified in 93.5% of the fields tested. Over this five-year period, the disease incidence averaged 32%. The highest incidence (34.8%) of eyespot was found in the Middle Lowland zone of Lithuania, the lowest (25.8%) was in the Eastern zone and an intermediate incidence (30.2%) was observed in the Western zone. During the 2010–2012 period, Oculimacula acuformis was the most prevalent Oculimacula spp. in the majority of triticale crops inspected. Only in 3 cases out of 27 was the amount of Oculimacula yallundae DNA higher than that of O. acuformis. According to our results, the incidence of eyespot in triticale varied greatly and could be of economic importance in some fields. The predominance of O. acuformis over O. yallundae is an important consideration in the choice of fungicides for eyespot control.     

腐殖酸对Mycobacterium sp. NJS-1降解芘的影响

为研究腐殖酸(Humic acid,HA)对微生物降解环境中多环芳烃(Polycyclic Aromatic Hydrocarbons,PAHs)的影响,以四环芘为典型PAHs及HA为代表性溶解性有机质,选取芘高效降解菌Mycobacterium sp. NJS-1于有无HA条件下降解芘,应用傅里叶变换回旋离子共振质谱(FT-ICR-MS),激光共聚焦显微镜(CLSM),及光谱技术分析降解过程中芘的残留特征、中间产物信息及菌落的变化特征。结果显示：未添加HA,芘降解率为35.33%±3.27%;添加HA后,其降解率明显提高,达到88.33%±3.40%,表明HA对高效菌Mycobacterium sp. NJS-1降解芘有明显的促进作用。不添加HA,菌落Mycobacterium sp. NJS-1分泌的双加氧酶只进攻芘的C_4,5位点,而添加HA后增加了进攻芘的C_1,2位点,因此增加了芘的代谢途径。添加HA后,CLSM结果显示无死亡细胞出现而且团聚明显,表明HA能够提高细胞的存活率并促进微生物膜的形成。同时,在降解芘的过程中,产生了酪氨酸类蛋...     

基因宏阵列和荧光定量PCR方法对西瓜枯萎病害土壤中尖孢镰刀菌的快速检测和定量

采用基因宏阵列(Macroarray)和荧光定量PCR(Real-time PCR)的方法,对引起西瓜枯萎病害的病原菌尖孢镰刀菌(Fusarium oxysporum)进行了快速监测和快速绝对定量,并且对实验条件进行了优化和摸索。结果显示,在西瓜枯萎病害发病较为严重的处理N-+P-和N-+P+的根际土壤中,Macroarray检测到强烈的阳性信号,表明尖孢镰刀菌的大量存在,同时荧光定量PCR的结果也表明在这两个处理的根际土壤中尖孢镰刀菌数量最多,分别为每g土壤8.89×105和2.24×105个拷贝数;而在未发生枯萎病害的处理N++P-和N++P+中,Macroarray未检测到阳性信号,根际土壤中尖孢镰刀菌数量分别为每g土壤6.23×103和3.28×103个拷贝数;而四个处理的土体土壤中尖孢镰刀菌的数量均维持在每g土壤102～103个拷贝数,Macroarray未检测到阳性信号。与传统检测方法如病原菌的分离培养、平板稀释计数等相比,上述分子生物学方法对病原真菌的检测和定量更为准确快速、省时省力。     

硫杆菌以及好养异养型硫氧化菌对元素硫的氧化

The prediction of the oxidation rate of elemental sulfur (S⁰) is a critical step in sulfur (S) fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S⁰ oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S⁰ applied to the soil were oxidized at 20 and 30 ℃, respectively. The oxidation of S⁰ proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm^-2 d^-1 was measured during the first two weeks at 30 ℃. At 20 ℃ the highest oxidation rate of 10.2 μg S cm^-2 d^-1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S⁰ the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 10⁵ and 1.4 × 10⁵ g^-1 soil at the start of the experiment to 4 × 10⁸ and 5.6 × 10⁸ g^-1 soil 14 days after S⁰ application, respectively. No Thiobacillus spp. was present eight weeks after S⁰ application. The results suggested that oxidation of residual S⁰ completely relied on aerobic heterotrophic S-oxidizing bacteria.     

Transfer and loss of naturally-occurring plasmids among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils

Plasmid transfer among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils from a long-term experiment in Braunschweig, Germany, was investigated under laboratory conditions. Three replicate samples each of four sterilized soils with total Zn contents of 54, 104, 208 and 340 mg kg⁻¹ were inoculated with an equal number (1×10⁵ cells g⁻¹ soil) of seven different, well-characterized isolates of R. leguminosarum bv. viciae. Four of the isolates were from an uncontaminated control plot (total Zn 54 mg kg⁻¹) and three were from a metal-contaminated plot (total Zn 340 mg kg⁻¹).After 1 year the population size was between 10⁶ and 10⁷ g⁻¹ soil, and remained at this level in all but the most contaminated soil. In the soil from the most contaminated plot no initial increase in rhizobial numbers was seen, and the population declined after 1 year to <30 cells g⁻¹ soil after 4 years. One isolate originally from uncontaminated soil that had five large plasmids (no. 2-8-27) was the most abundant type re-isolated from all of the soils. Isolates originally from the metal-contaminated soils were only recovered in the most contaminated soil. After 1 year, four isolates with plasmid profiles distinct from those inoculated into the soils were recovered. One isolate in the control soil appeared to have lost a plasmid. Three isolates from heavy metal contaminated soils (one isolate from the soil with total Zn 208 mg kg⁻¹ and two isolates from the soil with total Zn 340 mg kg⁻¹) had all acquired one plasmid. Plasmid transfer was confirmed using the distinct ITS-RFLP types of the isolates and DNA hybridization using probes specific to the transferred plasmid. The transconjugant of 2-8-27 which had gained a plasmid was found in one replicate after 2 years of the most contaminated soil but comprised more than 50% of the isolates. A similar type appeared in a separate replicate of the most contaminated soil after 3 years and persisted in both of these soils until the final sampling after 4 years. After 2 years isolates were recovered from four of the soil replicates with the chromosomal type of 2-8-27 which appeared to have lost one plasmid, but these were not recovered subsequently.Isolate 2-8-27 was among the isolates most sensitive to Zn in laboratory assays, whereas isolate 7-13-1 showed greater zinc tolerance. Acquisition of the plasmid conferred enhanced Zn tolerance to the recipients, but transconjugant isolates were not as metal tolerant as 7-13-1, the putative donor. Laboratory matings between 2-8-27 and 7-13-1 in the presence of Zn resulted in the conjugal transfer of the same small plasmid from 7-13-1 to isolate 2-8-27 and the transconjugant had enhanced metal tolerance. Our results show that transfer of naturally-occurring plasmids among rhizobial strains is stimulated by increased metal concentrations in soil. We further demonstrate that the transfer of naturally-occurring plasmids is important in conferring enhanced tolerance to elevated zinc concentrations in rhizobia.     

Diversity and antagonistic potential of Pseudomonas spp. associated to the rhizosphere of maize grown in a subtropical organic farm

Pseudomonas spp. are one of the most important bacteria inhabiting the rhizosphere of diverse crop plants and have been frequently reported as biological control agents (BCAs). In this work, the diversity and antagonistic potential of Pseudomonas spp. in the rhizosphere of maize cultivars Nitroflint and Nitrodent grown at an organic farm in Brazil was studied by means of culture-dependent and -independent methods, respectively. Sampling of rhizosphere soil took place at three different stages of plant development: 20, 40 and 106 days after sowing. A PCR-DGGE strategy was used to generate specific Pseudomonas spp. fingerprints of 16S rRNA genes amplified from total community rhizosphere DNA. Shifts in the relative abundance of dominant populations (i.e. PCR-DGGE ribotypes) along plant development were detected. A few PCR-DGGE ribotypes were shown to display cultivar-dependent relative abundance. No significant differences in diversity measures of DGGE fingerprints were observed for different maize cultivars and sampling times. The characterisation and assessment of the antagonistic potential of a group of 142 fluorescent Pseudomonas isolated from the rhizosphere of both maize cultivars were carried out. Isolates were phenotypically and genotypically characterised and screened for in vitro antagonism towards three phytopathogenic fungi and the phytopathogenic bacterium Ralstonia solanacearum. Anti-fungal activity was displayed by 13 fluorescent isolates while 40 isolates were antagonistic towards R. solanacearum. High genotypic and phenotypic diversity was estimated for antagonistic fluorescent Pseudomonas spp. PCR-DGGE ribotypes displayed by antagonists matched dominant ribotypes of Pseudomonas DGGE fingerprints, suggesting that antagonists may belong to major Pseudomonas populations in the maize rhizosphere. Antagonists differing in their genotypic and phenotypic characteristics shared the same DGGE electrophoretic mobility, indicating that an enormous genotypic and functional diversity might be hidden behind one single DGGE band. Cloning and sequencing was performed for a DGGE double-band which had no corresponding PCR-DGGE ribotypes among the antagonists. Sequences derived from this band were affiliated to Pseudomonas stutzeri and P. alcaligenes 16S rRNA gene sequences. As used in this study, the combination of culture-dependent and -independent methods has proven to be a powerful tool to relate functional and structural diversity of Pseudomonas spp. in the rhizosphere.     

菲对秀丽隐杆线虫、中杆属和拟丽突属线虫毒性效应研究

采用悉生培养系统,研究不同浓度菲对秀丽隐杆线虫、拟丽突属与中杆属线虫的毒性效应,以及3种线虫对菲的去除作用。结果表明:(1)随着菲浓度的增加,3种线虫存活率逐渐降低。秀丽隐杆线虫在不添加菲的处理中,48 h内出现繁殖,而在添加菲的处理中,即使在最低浓度5 mg/L下,繁殖现象也会消失。中杆属与拟丽突属线虫由于世代时间较长,在本试验周期内均未出现繁殖现象。(2)暴露24 h时,比较不同浓度菲处理下线虫的相对死亡率,得到3种线虫的耐性依次为中杆属线虫≥秀丽隐杆线虫≥拟丽突属线虫,且随菲浓度的增加,秀丽隐杆线虫耐性水平逐渐降低;暴露48 h时中杆属线虫耐性依旧高于拟丽突属,而72 h时中杆属与拟丽突属线虫的耐性趋于一致。(3)3种线虫受菲胁迫后均失去头部正常摆动能力,且秀丽隐杆线虫与拟丽突属线虫体长随菲浓度的增加而逐渐降低。(4)不同种类线虫的添加均能促进菲的去除,不同线虫之间无显著差异。因此,菲会显著抑制3种线虫的存活率和生长发育,抑制秀丽隐杆线虫的繁殖。线虫的存活率受线虫种类、暴露时间、菲浓度及其交互作用的影响显著,其中中杆属线虫对菲的综合耐性最强,3种线虫均能促进溶液中菲的去除。     

二苯醚类除草剂降解菌Bacillus sp. Za微生物制剂的研发与初步应用

以二苯醚类除草剂高效降解菌株Bacillus sp. Za为材料制备微生物制剂，优化液体制剂保护剂的物质配比，筛选固体制剂的最适材料，对固体制剂进行初步应用并评价其降解效果。研究结果表明：（1）液体制剂保护剂（0.20%柠檬酸钠、0.20%羧甲基纤维素、0.30% KCl）可使活菌数提高35.71%，保存30 d的液体制剂对50 mg/L乳氟禾草灵的降解率为83.50%。（2）筛选得到猪粪有机肥作为固体制剂的最适材料，保存60 d时固体制剂活菌数为8.26×108 cfu/g，对土壤中10 mg/kg乳氟禾草灵的降解率为85.52%。（3）添加固体制剂可有效缓解乳氟禾草灵残留对玉米所产生的药害。     

Quantification of the biocontrol agent Pseudomonas fluorescens Pf153 in soil using a quantitative competitive PCR assay unaffected by variability in cell lysis- and DNA-extraction efficiency

Although often neglected, variability in cell lysis efficiency and DNA extraction yield represents the major hurdles of any polymerase chain reaction (PCR)-based quantification protocol in soil and other natural environments. In this study we developed a technique that minimizes the effects of these constraints, providing at the same time a reliable internal control to distinguish between PCR-inhibition and negative results. We used Pseudomonas fluorescens Pf153, a root-colonizing bacterium that shows biocontrol activity against tobacco and cucumber black root rot, as the target organism for PCR quantification. Prior to DNA extraction, the genetically engineered, cognate reference strain P. fluorescens CHA0/c2 was inoculated in a reference soil. CHA0/c2 in the reference soil and Pf153 in the soil sample were lysed in parallel and afterward the lysates were mixed in known proportions. CHA0/c2 carries the plasmid pME6031-cmp2 that contains an allelic variant (competitor) of the Pf153 specific sequence Pf153_2. In a quantitative competitive PCR (QC-PCR) assay the competitor allows the quantification of the target strain down to 0.66 Pf153 CFU/mg soil. Processing the reference strain in the same way as Pf153 enables the exact quantification of the target strain in biocontrol assays performed in natural soil, overcoming differences in DNA extraction efficiency and PCR amplification from different soil environments. This technique is easily adaptable to other Pseudomonas strains simply by replacing the competitor used here with one derived from a SCAR-marker which is specific for the strain of choice.     

Root colonization and growth promotion of wheat and maize by Pseudomonas aurantiaca SR1

Wheat (Triticum aestivum L.), rice (Oryza sativa) and maize (Zea mays L.) are the most important cereals worldwide. However, in the last few years, soil has been submitted to both use and handling pressures due to the increase in agricultural practices, which are leading to its degradation. The use of plant growth-promoting rhizobacteria (PGPR) as inoculants constitutes a biological alternative for sustainable production. Pseudomonas aurantiaca SR1 was formulated as an inoculant in order to evaluate its growth promotion effect in the field when applied on maize and wheat seeds at the sowing time. P and N fertilization treatments were also included in the assays. P. aurantiaca SR1 colonized the root system of both crops and it persisted at appropriate population densities. It also showed a significant plant growth-promoting effect that was reflected in the yield. Another relevant finding was that both crops, when inoculated with P. aurantiaca SR1, presented higher yields with fertilization doses lower than those conventionally applied. This indicated its potential use as a reasonable alternative for crop production, with a minimization of the ecological impact.     

生物耕作对土壤理化特性、酶活性及青花菜生长和品质的影响

通过田间试验,研究生物耕作(接种蚯蚓)对土壤理化性质、酶活性及青花菜生长和产量品质的影响。试验设置了传统机械旋耕(CK)、免耕(T1)以及生物耕作(T2)3个处理。研究结果表明:(1)生物耕作能有效提高耕层不同部位的土壤养分含量和含水量,其中尤以5～20 cm土层较为明显,生物耕作处理土壤有机质、全氮、有效磷含量以及含水量依次比传统机械旋耕(CK)增长58.33%、68.93%、67.06%和16.19%;与传统机械旋耕(CK)相比,生物耕作处理大大提升了土壤过氧化氢酶、脲酶以及蔗糖酶的活性,其中脲酶、蔗糖酶与CK之间差异显著(P<0.05)。(2)生物耕作处理下青花菜的株高、开展度、叶长、叶宽等指标与CK和T1之间差异显著(P<0.05);各处理间青花菜的叶绿素相对含量差异不大,生物耕作处理增强了青花菜在各生长期的净光合速率。(3)生物耕作处理大幅提高了青花菜品质,生物耕作处理下的青花菜Vc含量是CK的1.2倍,硫代葡萄糖苷含量分别比T1处理和CK高1.05 mol·g-1和3.29 mol·g-1,差异均达到显著水平;各处理间可溶性糖含量差异不显著。因此,在传统的农业生态系统中,培育土壤有益动物的生物数量(生物耕作)可提高土壤养分和酶活性,对改善农田土壤肥力有着重要意义。     

土壤因子对链霉菌S506定殖和促生功能的影响

链霉菌S506是从植物根际分离获得的具有促生、防病和降解根系毒素功能的根际微生物,为了解土壤环境条件对其在根际定殖和功能表达的影响,以链霉菌S506为试材,研究了土壤质地、环境温度和土壤湿度对S506在番茄根际土壤定殖及番茄植株生长的影响.结果表明,适宜链霉菌S506在番茄根际定殖和促生作用发挥的土壤质地为壤土,其次为砂土和黏土;试验所设温度梯度中,利于S506在根际定殖的环境温度为30℃,其次为22.5℃和15℃,而利于目的菌株促生功能表达的环境温度则依次为22.5℃、30℃和15℃;适宜于目的菌株在根际定殖和促生功能发挥的土壤相对湿度为20%、25%,其次为15%和30%.