The Effect of Seed Bacterization by Bacillus Cohn Bacteria on Their Colonization of the Spring Wheat Rhizosphere

The dynamics of introduced antagonistic bacteria in the spring wheat rhizosphere was studied in small-plot field experiments during several growing seasons. The population density of the introduced bacteria was found to depend considerably on the inoculum dose. At sufficiently high inoculum doses, the introduced bacteria remained in the wheat rhizosphere over the entire vegetative period (88–109 days). The maximum population density of the introduced bacteria was observed in the early terms of plant development. No correlation was found between the population density of the introduced bacteria and the degree of suppression of root rot or the structural crop yield parameters. The beneficial effect of preplanting seed bacterization on wheat plants was, as a rule, profound only during unfavorable growing seasons.     

Microorganisms in the rhizosphere of wheat colonized by the fungusGaeumannomyces graminis var.tritici

The population of microorganisms in wheat rhizosphere changed in the presence of the fungus Gaeumannomyces graminis var. tritici causing the take-all of wheat. In the majority of cases when the soil was artificially contaminated by the fungus, both the number of bacteria in the rhizosphere and the bacteria/fungi ratio temporarily increased. At the beginning bacteria growing in the presence of NH4+ predominated, later bacteria utilizing organic N-substances prevailed. Pseudomonas fluorescens and the related species colonized the rhizosphere and the soil to a greater extent in the presence of G. graminis. The wheat rhizosphere with G. graminis was found to contain a higher level of the slime-producing bacterium Agrobacterium spp.; this microorganism occurred on hyphal surfaces (in hyphosphere) of both G. graminis growing in soil and Mucor spp. Changes in microbial populations in the wheat rhizosphere during the first stage of colonization by G. graminis can be partly explained by a simultaneous rhizosphere colonization by microorganisms which accompany this fungus in soil. In the period of increase in the number of bacteria in rhizosphere a temporary stimulation of wheat growth was observed.     

Inoculum Density and Population Dynamics of Suppressive and PathogenicStreptomycesStrains and Their Relationship to Biological Control of Potato Scab

SeveralStreptomycesstrains are capable of suppressing potato scab caused byStreptomyces scabies.Although these strains have been successful in the biocontrol of potato scab in the field, little is known about how populations of pathogenicStreptomycesin the potato rhizosphere are influenced by inoculation of the suppressive strains. The effects of inoculum densities of pathogenic and suppressiveStreptomycesstrains on their respective populations on roots and in rhizosphere soil were examined during the growing season. The relationships between inoculum density or rhizosphere population densities and disease severity were also investigated. Populations of suppressiveStreptomycesstrain 93 increased significantly on roots with increasing inoculum dose. At its highest inoculum dose, the suppressive strain reached a population density greater than 10⁶CFU/g root 14 weeks after planting. The ability of the suppressive strain to increase its populations with increasing inoculum density was hindered at high inoculum doses of the pathogen, suggesting that density-dependent competitive interactions may be occurring between the two antagonists. Strain 93 was most effective at preventing scab early in the growing season (8 weeks after planting), when tubers were most susceptible to the scab disease. Population densities of the suppressive strain in soil were more highly negatively correlated with scab severity than were populations on roots, suggesting that rhizosphere soil rather than potato roots may be the primary source of inoculum of the suppressive strain for tubers.     

Irrigation differentially impacts populations of indigenous antibiotic-producing pseudomonas spp. in the rhizosphere of wheat

This work determined the impact of irrigation on the seasonal dynamics of populations of Pseudomonas spp. producing the antibiotics phenazine-1-carboxylic acid (Phz(+)) and 2,4-diacetylphloroglucinol (Phl(+)) in the rhizosphere of wheat grown in the low-precipitation zone (150 to 300 mm annually) of the Columbia Plateau of the Inland Pacific Northwest. Population sizes and plant colonization frequencies of Phz(+) and Phl(+) Pseudomonas spp. were determined in winter and spring wheat collected during the growing seasons from 2008 to 2009 from selected commercial dryland and irrigated fields in central Washington State. Only Phz(+) bacteria were detected on dryland winter wheat, with populations ranging from 4.8 to 6.3 log CFU g(-1) of root and rhizosphere colonization frequencies of 67 to 100%. The ranges of population densities of Phl(+) and Phz(+) Pseudomonas spp. recovered from wheat grown under irrigation were similar, but 58 to 100% of root systems were colonized by Phl(+) bacteria whereas only 8 to 50% of plants harbored Phz(+) bacteria. In addition, Phz(+) Pseudomonas spp. were abundant in the rhizosphere of native plant species growing in nonirrigated areas adjacent to the sampled dryland wheat fields. This is the first report that documents the impact of irrigation on indigenous populations of two closely related groups of antibiotic-producing pseudomonads that coinhabit the rhizosphere of an economically important cereal crop. These results demonstrate how crop management practices can influence indigenous populations of antibiotic-producing pseudomonads with the capacity to suppress soilborne diseases of wheat.     

Relationship between the number of bacteria added to soil or seeds and their abundance and distribution in the rhizosphere of alfalfa

A study was conducted of the relationship between the density of several bacterial strains introduced into soil or onto seeds and their abundance in the rhizosphere of alfalfa. The abundance of six species in the rhizosphere was directly correlated with the density of bacteria initially added to soil. The density of six species in the rhizosphere of 15-day-old plants also was directly correlated with the density of each strain in nonrhizosphere soil. Tests of seven species added to soil at four inoculum densities showed that bacteria that survived well in the soil attained the highest densities in the rhizosphere and those that survived poorly in the soil were present at the lowest densities in the rhizosphere. Sixteen of 19 bacterial strains added to alfalfa seeds at 10⁷ or 10⁸ cells per g colonized the rhizosphere of 15-day-old plants, but nearly all of the cells were localized in the upper third of the rhizosphere. A study of 12 bacterial strains that failed to colonize the lower part of the rhizosphere if inoculated onto seeds showed that the bacteria colonized the entire rhizosphere of 15-day-old alfalfa plants if initially inoculated throughout the soil. The data suggest that the density of individual bacterial strains in the rhizosphere is dependent on their density in the soil and that seed inoculation only has an effect on the population in the proximal portion of the alfalfa root system.     

Bacterial conjugation between pseudomonads in the rhizosphere of wheat

Abstract Transfer of plasmid RP4 between introduced pseudomonads was studied in rhizosphere and non-rhizosphere soil of wheat, in soil chambers and in culture tubes. In both experiments, the presence of growing wheat roots stimulated the occurrence of plasmid transfers in the soil. The plasmid transfer frequencies in rhizosphere soil in the soil chambers were consistently higher than those in rhizosphere soil in the culture tubes, indicating an influence of the experimental set-up.
In the soil chambers, both the survival of introduced donor and recipient strains and the plasmid transfer frequencies decreased drastically at increasing distances from the roots. In addition, plasmid transfer frequencies were influenced by the inoculum densities of both donor and recipient strains; higher frequencies were observed in soil that was initially inoculated with higher cell numbers.     

Effect of temperature and soil moisture content on the colonization of the wheat rhizosphere by antiphytopathogenic bacilli

Vegetative experiments showed that the population density of antiphytopathogenic bacillar species introduced into the rhizosphere of spring wheat seedlings essentially depended on the soil temperature and not on the soil moisture content. As a rule, the population of introduced bacilli increased with the temperature. Under both low and optimal soil moisture contents, introduced bacilli were efficiently acclimated in the wheat rhizosphere.     

Effect of temperature and soil moisture content on the colonization of the wheat rhizosphere by antipytopathogenic Bacillus Cohn

Vegetative experiments showed that the population density of antiphytopathogenic bacillar species introduced into the rhizosphere of spring wheat seedlings essentially depended on soil temperature and not on the soil moisture content. As a rule, the population of introduced bacilli increased with temperature. Under both low and optimal soil moisture contents, introduced bacilli were efficiently acclimated in the wheat rhizosphere.     

Relationships between plant roots,proteolytic organisms and activity of protease

Proteolytic bacteria represented 18–58% of the bacterial population isolated from the rhizoplane of different crops. The activity of protease was considerably higher on roots of wheat growing in the soil than in the rhizosphere or free soil. However, only a slightly positive rhizosphere effect in the relative occurrence of casein-hydrolyzing bacteria could be observed. An indirect relationship between numbers of bacteria hydrolyzing casein and the activity of the enzyme could be found. The activity of protease related to a unit of culturable proteolytic bacteria was considerably higher on the root than in the rhizosphere and in the soil. A relationship between characteristics of the production of the enzyme by proteolytic bacteria and the protease activity on the surface of roots was demonstrated. The resulting enzyme activity on the surface of roots depended apparently on growth conditions of the plant and nature of root exudates and was influenced both by inactivation and protection due to adsorption of the enzyme by roots.     

Soft rot Erwinia bacteria in the rhizosphere of weeds and crop plants in Colorado, United States and Scotland

The soft rot coliform bacteria Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica were isolated by an enrichment method from the rhizosphere of many weed species and crop plants, collected in commercial potato fields either currently in potatoes or in a different crop as part of the rotation. Erwinia carotovora was isolated from 24 plant species in Colorado and 47 species in Scotland. Weeds contaminated with E. carotovora were found in fields growing other crops in which potatoes had not been grown for 1–2 and sometimes much longer. Weeds collected from virgin land in Colorado were not contaminated with E. carotovora but in Scotland virgin soils containing weed roots yielded E. carotovora subsp. carotovora . In general, the numbers of contaminated weeds rose from nil or low levels in spring and early summer to considerably higher levels during mid-season, and fell to progressively lower levels later. Erwinia carotovora subsp. carotovora was the predominant organism recovered from the rhizosphere, but E. carotovora subsp. atroseptica was less common, especially in Scotland, and its incidence varied in different seasons depending on factors such as temperature and moisture conditions. The bacteria could apparently persist in the root zone for an extended period of time and may be a source of inoculum to contaminate soft rot erwinia-free seed potato stocks; the origin of the bacteria was uncertain.     

Biochemical weathering of calcium-bearing minerals by rhizosphere micro-organisms,and its influence on calcium accumulation in trees

Summary The rhizosphere microflora of redcedar was found to have a higher percentage of calcium silicate-solubilizing rhizosphere bacteria than the rhizosphere microflora of white pine of similar age growing in the same locality under identical conditions. Though the species composition of the silicatesolubilizing microbial population varied considerably from winter to spring, the redcedar roots had more silicate-solubilizers than the white pine roots inboth seasons. Since redcedar is known to have a higher calcium content than white pine, these results indicate that calcium accumulation by redcedar and white pine is strongly influenced by the rate at which calcium is released from soil minerals by the weathering action of the trees' rhizosphere micro-organisms. A symbiotic relationship between the trees and the microflora is suggested.     

Characterization of rhizosphere colonization by luminescent Enterobacter cloacae at the population and single-cell levels.

A bioluminescence marker system was used to characterized colonization of the rhizosphere by a bacterial inoculum, both in terms of population activity and at the single-cell level. Plasmid pQF70/44, which contains luxAB genes under the control of a strong constitutive phage promoter, was introduced into the rhizobacterium and model biocontrol agent Enterobacter cloacae. Light output from the lux-modified strain was detected by luminometry of samples from growing cultures of E. cloacae and from inoculated soil and wheat root samples. The minimum detection limits for fully active cells under optimum conditions were 90 and 445 cells g-1 for liquid culture and soil, respectively. The metabolic activities of the lux-marked population of E. cloacae, characterized by luminometry, contrasted in rhizosphere and nonrhizosphere soil. Cells in the rhizosphere were active, and there was a linear relationship between light output and cell concentration. The activity of cells in nonrhizosphere coil could not be detected unless the soil was supplied with substrate. Novel use of a charge-coupled device is reported for the spatial characterization of rhizosphere colonization by E. cloacae (pQF70/44) at the single-cell and population levels. Used macroscopically, the charge-coupled device identified differences in colonization due to competition from indigenous soil organisms. The lux-marked bacterium was able to colonize all depths of roots in the absence of competition but was restricted tot he spermosphere in the presence of competition (nonsterile soil).(ABSTRACT TRUNCATED AT 250 WORDS)     

Monitoring temporal and spatial variation in rhizosphere bacterial population diversity: A community approach for the improved selection of rhizosphere competent bacteria

The potential for developing a reliable strategy for selecting rhizosphere competent bacteria, based on an improved understanding of the community diversity and population dynamics of fluorescent pseudomonads, was investigated. Isolates from a collection of over 690 fluorescent pseudomonads, obtained from sugar beet and wheat plants grown in field soils in laboratory microcosms, were genotypically and phenotypically characterised. RFLP rRNA analysis (ribotyping) revealed that the sampled population was composed of 385 related but distinct ribotypes. Most ribotypes were isolated only once and represented a transient colonising population. However, representatives of 26 ribotypes were detected more often, of which five were isolated from rhizosphere soils sampled 7 months after the first sampling. Comparative phenotypic analysis of isolates (motility, antibiotic resistance and production, adherence, fatty acid composition, substrate utilisation patterns) demonstrated that the ability to utilise organic acids as carbon sources correlated with rhizosphere competence. Single inoculum and competitive colonisation studies in planted microcosms confirmed rhizosphere competence, but also demonstrated synergistic interactions. The colonisation ability and population densities of transient strains were significantly increased when co-inoculated with rhizosphere competent isolates. These data demonstrate potential cross-feeding and combined niche exploitation, rather than direct competition, confirming the multi-factorial nature of rhizosphere competence in diverse fluorescent pseudomonad communities. They also highlight the need to consider the use of mixed inocula for plant growth promotion and the systematic selection of strains for effective biotechnological exploitation.     

小麦/玉米轮作田根际微生物多样性分析

【背景】小麦/玉米轮作是中国粮食作物主要种植模式之一,目前对小麦/玉米轮作田根际土壤微生物差异变化缺乏全面的了解。【目的】明确小麦/玉米根际土壤微生物差异变化并了解其潜在功能。【方法】以小麦/玉米根际土壤为材料,运用细菌16S rRNA基因和真菌rDNA ITS基因测序,分析小麦/玉米根际土壤微生物多样性。【结果】玉米季微生物丰富度高于小麦季,而多样性无明显差异。放线菌门(Actinobacteria)、变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)和绿弯菌门(Chloroflexi)为小麦季和玉米季根际土壤的优势细菌门,优势真菌门为子囊菌门(Ascomycota)。小麦季和玉米季共有细菌和真菌分别是631个和261个,小麦季特有细菌和真菌分别是38个和58个,玉米季特有细菌和真菌分别是25个和39个。LEfSe分析(LDA阈值为2)细菌和真菌表明,放线菌纲(Actinobacteria)和微囊菌目(Microascales)在小麦季富集,鞘脂单胞菌目(Sphingomonadales)和银耳纲(Tremellomycetes)在玉米季富集。小麦季、玉...     

土壤食细菌线虫与细菌的相互作用及其对N、P矿化生物固定的影响及机理

采用悉生微缩体系,研究了４０ｄ 培养期内不添加外源基质条件下食细菌线虫（Ｐｒｏｔｏｒｈａｂｄｔｉｓ ｓｐ．）和细菌（Ｐｓｅｕｄｏｍ ｏｎａｓｓｐ．）的相互作用及其对Ｎ、Ｐ转化的影响。在种植及不种植小麦的土壤中,发现接种线虫后细菌数量显著增加,非根标土壤细菌的增加量又比根际土明显。在种植小麦体系中,根际与非根际土壤线虫均比不种作物体系有增加趋势,其中根际土壤线虫种群的提高尤为显著。只加细菌处理中土壤Ｎ、Ｐ均无净矿化,相反培养前期出现轻微的生物固定。线虫的引入显著提高了土壤矿质Ｎ、微生物量Ｎ 和微生物量Ｐ的含量,但对土壤有效Ｐ影响很小。这表明线虫活动主要是促进了Ｎ的矿化,而Ｐ表现出较强的生物固定。文中还分析了线虫捕食对细菌的增殖作用以及线虫——细菌相互作用在Ｎ、Ｐ矿化和生物固定中的机理。     

两种镉积累型小麦根际微生物群落结构及功能多样性

为探究不同积累型小麦品种对根际微生物群落结构及功能多样性的影响,以镉低积累型小麦济麦22和镉高积累型小麦冀5265为研究材料,采用分离培养法和Biolog-Eco微平板法分析根际细菌数量、可培养优势群落结构以及微生物群落功能多样性。结果表明：污染土壤济麦22根际总细菌数量和抗Cd细菌数量均显著高于冀5265,而非污染土壤中两品种间无差异。污染土济麦22根际发现较多产脲酶和高镉抗性菌株(200 mg/L)。污染土济麦22根际优势菌多为Arthrobacter sp.和Bacillus sp.,冀5265根际优势菌主要为Streptomyces sp.;非污染土济麦22与冀5265根际优势菌群相似,均以Bacillus sp.为主。Biolog试验结果表明,两个小麦品种根际微生物群落对碳源的利用能力存在差异,济麦22根际微生物AWCD值、Mc Intosh指数、Shannon-Wiener指数、Simpson指数在污染土和无污染土中均显著高于冀5265。因此,污染土壤中不同积累型小麦品种根际微生物群落结构及功能多样性均存在差异,该研究结果对于揭示高低积累型小麦根际微生物机制提供了重要参考依...     

Sexual reproduction of Zymoseptoria tritici on durum wheat in Tunisia revealed by presence of airborne inoculum,fruiting bodies and high levels of genetic diversity

Septoria tritici blotch (STB) caused by the heterothallic ascomycete Zymoseptoria tritici is currently one of the most devastating diseases of wheat worldwide. The extent of sexual reproduction of this pathogen is well documented on bread wheat, but not on durum wheat. The objective of the present study was to quantify the occurrence of Z. tritici sexual reproduction on durum wheat in the Tunisian environment. The assessment was undertaken using a triple approach combining fruiting body assessment, ascospore trapping and population genetic analyses. The results highlighted the formation of pseudothecia on leaves and stubble from the autumn until the end of the growing season. Likewise, qPCR monitoring highlighted a constant release of Z. tritici airborne inoculum during the wheat-growing season, with a peak of production at the end of the season. Genetic investigations using microsatellites revealed high levels of gene and genotypic diversities, an equal distribution of mating types, and a lack of genetic clustering within and between growing seasons. Taken together, these findings indicate that Z. tritici undergoes sexual reproduction on durum wheat in Tunisia at least to the same extent than on bread wheat in Western Europe, and that the dry and warm climate does not affect the mating process of the fungus. Frequent occurrence of sexual reproduction is a valuable knowledge to take into account in STB control strategies on durum wheat.     

Seasonal variation of phenol/benzoate-degrading iron-reducing bacteria in irrigated tropical paddy soils as affected by some management practices

The study provides the first evidence of the presence and abundance of bacterial population that coupled ferric iron reduction to aromatic compounds degradation in tropical irrigated paddy soils in the Philippines. Culturable phenol/benzoate degrading iron-reducing bacteria was enumerated by the most probable number (MPN) counts using phenol or benzoate as sole carbon source, and ferric oxide [Fe(OH)(3)] as the sole electron acceptor. Population density of phenol degrading iron-reducing bacteria (P-IRB) in irrigated paddy soil ranged from 10(2) to 10(8)g(-1) dry soil, and increased with the progressive rice growth in rice cropping seasons; the study also revealed a significant rhizosphere effect on population of P-IRB. However, high enumeration of benzoate degrading iron-reducing bacteria (B-IRB) was obtained in all the tested soil samples averaging at 1.2 x 10(6)g(-1) dry soil, and did not fluctuate significantly over the rice cropping seasons. Statistical data showed that less cropping density with aerated fallow and high nitrogen rate favored the population growth of P-IRB. However, results showed that population size of B-IRB was relatively insensitive to the effect of either seasonal or extrinsic factors tested in this study.     

Colonization potential of bacteria in the rhizosphere

The effect of inoculum density on growth and steady-state populations of aPseudomonas sp., aMycoplana sp., and aCurtobacterium sp. in the rhizosphere if gnotobiotic barley plants was studied. Inoculation of sterile barley seedling at concentrations of about 1×10³, 1×10⁵ and 1×10⁷ viable cells (mg dry wt root)^–1 resulted in rapid colonization; maximum populations of about 5×10⁷ viable cells (mg dry wt root)^–1 developed in each case. We define this maximum population as the colonization potential. Measurement of growth of known rhizosphere bacteria might be a useful index of the amount of available carbon and energy lost by growing roots.     

First Quantitative Study of Rove Beetles in Oklahoma Winter Wheat Fields

Adult rove beetles (Staphylinidae) were sampled every 7–14 days from one winter wheat field located in each of the four major wheat growing regions of Oklahoma during the 1999–2000 and 2000–2001 growing seasons. The number of cereal aphids per tiller, wheat plant growth stage, and wheat tiller density also were estimated. A total of 12 genera representing 13 species of beetles were collected from the field. The density of rove beetles was generally low, ranging from 0.003 beetles per m² in fall to 0.106 beetles per m² in spring. Rove beetle communities differed among seasons. After accounting for the effect of season, there was no statistically significant association between rove beetle community structure and field location, aphid density, wheat plant growth stage, or wheat plant density. Most rove beetle species showed no association with a particular season, however, Aleochara notula Erichson, Lathrobium sp., and Oxypoda sp. were present predominantly in fall, while Bisnius inquitus Erichson was associated with winter. Oxypoda sp. was the most abundant rove beetle in winter wheat fields in spring and was relatively abundant in winter, but was not collected from wheat fields in fall. Tachyporus jocosus Say was present in wheat fields during all seasons. T. jocosus was the most abundant rove beetle species in the winter wheat fields in fall and winter and was the second most abundant species during spring.