Plant-dependent genotypic and phenotypic diversity of antagonistic rhizobacteria isolated from different Verticillium host plants

To study the effect of plant species on the abundance and diversity of bacterial antagonists, the abundance, the phenotypic diversity, and the genotypic diversity of rhizobacteria isolated from potato, oilseed rape, and strawberry and from bulk soil which showed antagonistic activity towards the soilborne pathogen Verticillium dahliae Kleb. were analyzed. Rhizosphere and soil samples were taken five times over two growing seasons in 1998 and 1999 from a randomized field trial. Bacterial isolates were obtained after plating on R2A (Difco, Detroit, Mich.) or enrichment in microtiter plates containing high-molecular-weight substrates followed by plating on R2A. A total of 5,854 bacteria isolated from the rhizosphere of strawberry, potato, or oilseed rape or bulk soil from fallow were screened by dual testing for in vitro antagonism towards VERTICILLIUM: The proportion of isolates with antagonistic activity was highest for strawberry rhizosphere (9.5%), followed by oilseed rape (6.3%), potato (3.7%), and soil (3.3%). The 331 Verticillium antagonists were identified by their fatty acid methyl ester profiles. They were characterized by testing their in vitro antagonism against other pathogenic fungi; their glucanolytic, chitinolytic, and proteolytic activities; and their BOX-PCR fingerprints. The abundance and composition of Verticillium antagonists was plant species dependent. A rather high proportion of antagonists from the strawberry rhizosphere was identified as Pseudomonas putida B (69%), while antagonists belonging to the Enterobacteriaceae (Serratia spp., Pantoea agglomerans) were mainly isolated from the rhizosphere of oilseed rape. For P. putida A and B plant-specific genotypes were observed, suggesting that these bacteria were specifically enriched in each rhizosphere.     

Impact of Plant Species and Site on Rhizosphere-Associated Fungi Antagonistic to Verticillium dahliae Kleb.

Fungi with antagonistic activity toward plant pathogens play an essential role in plant growth and health. To analyze the effects of the plant species and the site on the abundance and composition of fungi with antagonistic activity toward Verticillium dahliae, fungi were isolated from oilseed rape and strawberry rhizosphere and bulk soil from three different locations in Germany over two growing seasons. A total of 4,320 microfungi screened for in vitro antagonism toward Verticillium resulted in 911 active isolates. This high proportion of fungi antagonistic toward the pathogen V. dahliae was found for bulk and rhizosphere soil at all sites. A plant- and site-dependent specificity of the composition of antagonistic morphotypes and their genotypic diversity was found. The strawberry rhizosphere was characterized by preferential occurrence of Penicillium and Paecilomyces isolates and low numbers of morphotypes (n = 31) and species (n = 13), while Monographella isolates were most frequently obtained from the rhizosphere of oilseed rape, for which higher numbers of morphotypes (n = 41) and species (n = 17) were found. Trichoderma strains displayed high diversity in all soils, but a high degree of plant specificity was shown by BOX-PCR fingerprints. The diversity of rhizosphere-associated antagonists was lower than that of antagonists in bulk soil, suggesting that some fungi were specifically enriched in each rhizosphere. A broad spectrum of new Verticillium antagonists was identified, and the implications of the data for biocontrol applications are discussed.     

Impact of plant species and site on rhizosphere-associated fungi antagonistic to Verticillium dahliae kleb

Fungi with antagonistic activity toward plant pathogens play an essential role in plant growth and health. To analyze the effects of the plant species and the site on the abundance and composition of fungi with antagonistic activity toward Verticillium dahliae, fungi were isolated from oilseed rape and strawberry rhizosphere and bulk soil from three different locations in Germany over two growing seasons. A total of 4,320 microfungi screened for in vitro antagonism toward Verticillium resulted in 911 active isolates. This high proportion of fungi antagonistic toward the pathogen V. dahliae was found for bulk and rhizosphere soil at all sites. A plant- and site-dependent specificity of the composition of antagonistic morphotypes and their genotypic diversity was found. The strawberry rhizosphere was characterized by preferential occurrence of Penicillium and Paecilomyces isolates and low numbers of morphotypes (n = 31) and species (n = 13), while Monographella isolates were most frequently obtained from the rhizosphere of oilseed rape, for which higher numbers of morphotypes (n = 41) and species (n = 17) were found. Trichoderma strains displayed high diversity in all soils, but a high degree of plant specificity was shown by BOX-PCR fingerprints. The diversity of rhizosphere-associated antagonists was lower than that of antagonists in bulk soil, suggesting that some fungi were specifically enriched in each rhizosphere. A broad spectrum of new Verticillium antagonists was identified, and the implications of the data for biocontrol applications are discussed.     

Bulk and Rhizosphere Soil Bacterial Communities Studied by Denaturing Gradient Gel Electrophoresis: Plant-Dependent Enrichment and Seasonal Shifts Revealed

The bacterial rhizosphere communities of three host plants of the pathogenic fungus Verticillium dahliae, field-grown strawberry (Fragaria ananassa Duch.), oilseed rape (Brassica napus L.), and potato (Solanum tuberosum L.), were analyzed. We aimed to determine the degree to which the rhizosphere effect is plant dependent and whether this effect would be increased by growing the same crops in two consecutive years. Rhizosphere or soil samples were taken five times over the vegetation periods. To allow a cultivation-independent analysis, total community DNA was extracted from the microbial pellet recovered from root or soil samples. 16S rDNA fragments amplified by PCR from soil or rhizosphere bacterium DNA were analyzed by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints showed plant-dependent shifts in the relative abundance of bacterial populations in the rhizosphere which became more pronounced in the second year. DGGE patterns of oilseed rape and potato rhizosphere communities were more similar to each other than to the strawberry patterns. In both years seasonal shifts in the abundance and composition of the bacterial rhizosphere populations were observed. Independent of the plant species, the patterns of the first sampling times for both years were characterized by the absence of some of the bands which became dominant at the following sampling times. Bacillus megaterium and Arthrobacter sp. were found as predominant populations in bulk soils. Sequencing of dominant bands excised from the rhizosphere patterns revealed that 6 out of 10 bands resembled gram-positive bacteria. Nocardia populations were identified as strawberry-specific bands.     

Evaluation of potential biocontrol rhizobacteria from different host plants of Verticillium dahliae Kleb

AIMS: A screening approach was developed to assess the potential of rhizobacterial strains to control Verticillium wilt caused by Verticillium dahliae Kleb. METHODS AND RESULTS: Sixty randomly chosen antagonistic bacterial strains originally isolated from rhizosphere of three different host plants of V. dahliae--strawberry, potato and oilseed rape--were evaluated for biocontrol and plant growth promotion by analysing in vitro antagonism towards V. dahliae and other plant pathogenic fungi, production of fungal cell wall-degrading enzymes and plant growth-promoting effects on strawberry seedlings. To test the plant growth-promoting effect, a microplate assay with strawberry seedlings was developed. Although the rhizobacterial strains were isolated from different plants they showed effects on the growth of strawberry seedlings. According to the in vitro biocontrol and plant growth-promoting activity, the three best candidates Pseudomonas putida B E2 (strawberry rhizosphere), Ps. chlororaphis K15 (potato rhizosphere) and Serratia plymuthica R12 (oilseed rape rhizosphere) were selected for greenhouse experiments to verify the in vitro screening results. Under greenhouse conditions the isolates selected according to this strategy were as effective, or more effective than commercial biocontrol agents and may therefore possibly be valuable as antagonists of V. dahliae. CONCLUSIONS: In this study, the screening strategy resulted in a selection of three interesting biocontrol candidates against Verticillium: Ps. putida B E2 (strawberry rhizosphere), Ps. chlororaphis K15 (potato rhizosphere) and Ser. plymuthica R12 (oilseed rape rhizosphere). SIGNIFICANCE AND IMPACT OF THE STUDY: A new combination of in vitro screening methods including a microplate assay with strawberry seedlings to test the plant growth promoting effect which allow to more efficiently select potential biological control agents was developed successfully.     

The rhizosphere effect on bacteria antagonistic towards the pathogenic fungus Verticillium differs depending on plant species and site

Rhizobacteria with antagonistic activity towards plant pathogens play an essential role in root growth and plant health and are influenced by plant species in their abundance and composition. To determine the extent of the effect of the plant species and of the site on the abundance and composition of bacteria with antagonistic activity towards Verticillium dahliae, bacteria isolated from the rhizosphere of two Verticillium host plants, oilseed rape and strawberry, and from bulk soil were analysed at three different locations in Germany over two growing seasons. A total of 6732 bacterial isolates screened for in vitro antagonism towards Verticillium resulted in 560 active isolates, among which Pseudomonas (77%) and Serratia (6%) were the most dominant genera. The rhizosphere effect on the antagonistic bacterial community was shown by an enhanced proportion of antagonistic isolates, by enrichment of specific amplified ribosomal DNA restriction analysis types, species and genotypes, and by a reduced diversity in the rhizosphere in comparison to bulk soil. Such an effect was influenced by the plant species and by the site of its cultivation. Altogether, 16S rRNA gene sequencing of 66 isolates resulted in the identification of 22 different species. Antagonists of the genus Serratia were preferentially isolated from oilseed rape rhizosphere, with the exception of one site. For isolates of Pseudomonas and Serratia, plant-specific and site-specific genotypes were found.     

Bulk and rhizosphere soil bacterial communities studied by denaturing gradient gel electrophoresis: plant-dependent enrichment and seasonal shifts revealed

The bacterial rhizosphere communities of three host plants of the pathogenic fungus Verticillium dahliae, field-grown strawberry (Fragaria ananassa Duch.), oilseed rape (Brassica napus L.), and potato (Solanum tuberosum L.), were analyzed. We aimed to determine the degree to which the rhizosphere effect is plant dependent and whether this effect would be increased by growing the same crops in two consecutive years. Rhizosphere or soil samples were taken five times over the vegetation periods. To allow a cultivation-independent analysis, total community DNA was extracted from the microbial pellet recovered from root or soil samples. 16S rDNA fragments amplified by PCR from soil or rhizosphere bacterium DNA were analyzed by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints showed plant-dependent shifts in the relative abundance of bacterial populations in the rhizosphere which became more pronounced in the second year. DGGE patterns of oilseed rape and potato rhizosphere communities were more similar to each other than to the strawberry patterns. In both years seasonal shifts in the abundance and composition of the bacterial rhizosphere populations were observed. Independent of the plant species, the patterns of the first sampling times for both years were characterized by the absence of some of the bands which became dominant at the following sampling times. Bacillus megaterium and Arthrobacter sp. were found as predominant populations in bulk soils. Sequencing of dominant bands excised from the rhizosphere patterns revealed that 6 out of 10 bands resembled gram-positive bacteria. Nocardia populations were identified as strawberry-specific bands.     

不同填闲模式对黄瓜根际土壤酶活性及细菌群落的影响

以温室连作3年黄瓜土壤为研究对象,以黄瓜为主栽作物,以青葱、小麦、油菜为不同季节填闲作物设置盆栽试验,采用常规化学方法、PCR-DGGE及qPCR技术,研究不同填闲模式对黄瓜土壤酶活性及细菌群落的影响.结果表明: 随着种植茬次的增加,填闲小麦处理的土壤脲酶、中性磷酸酶及转化酶活性均显著高于填闲青葱和油菜处理,同时油菜处理显著高于青葱处理;不同填闲模式间黄瓜根际土壤细菌群落结构不同,冬季填闲青葱和夏季填闲小麦处理维持了相对较高的多样性指数.qPCR检测结果表明: 随着种植茬次的增加,小麦处理的土壤细菌数量显著高于青葱和油菜处理.综上,不同填闲模式对土壤酶活性和细菌群落均产生一定影响,改变了土壤环境,其中夏季填闲小麦能保持相对较高的土壤酶活性、土壤细菌群落结构多样性及细菌数量.
     

基于高通量测序分析大豆和油菜根际微生物群落结构的差异

根肿病是由芸薹根肿菌侵染引起的专性寄生性土传病害,严重制约着油菜等十字花科作物的可持续生产.前期研究发现,大豆作为前茬作物可以显著降低后茬油菜根肿病的发生和危害,"豆-油轮作"模式是一种值得探索和应用的根肿病防治新途径.为了解开大豆作为前茬防治根肿病发生的机理,本研究基于扩增子测序技术探究大豆与油菜根际土壤微生物的群落结构差异.结果表明:大豆和油菜根际土壤微生物类群在门水平的优势类群相同,包括变形菌门、拟杆菌门、酸杆菌门、放线菌门、子囊菌门、接合菌门、担子菌门和壶菌门等丰度都较高.但相比于油菜根际土壤,大豆根际土壤富含具有生防作用和促进植物生长的微生物,如黄杆菌属、鞘脂单胞菌属、芽孢杆菌属、链霉菌属、假单胞菌属、木霉属和盾壳霉属等;而一些植物病原细菌(如肠杆菌、黄单胞菌)和真菌(炭疽菌和尾孢菌)含量则低于油菜根际土壤;另外,大豆根际土壤中还富含具有固氮功能的根瘤菌属、慢生根瘤菌属和丛枝菌根真菌(如球囊霉属).可见,大豆根际土壤利于有益微生物生长并可抑制病原菌繁殖.大豆和油菜根际微生物组差异为大豆-油菜轮作防治根肿病提供了理论依据,并为根肿病的防治提供了一些潜在的生物防治资源.     

The relation between oilseed rape and pollination of later flowering plants varies across plant species and landscape contexts

Increasing cultivation of oilseed rape may have consequences for pollinators and wild plant pollination. By providing pollinating insects with pollen and nectar, oilseed rape benefits short-tongued, generalist insect species. Long-tongued bumble bee species, specialized to other flower types, may instead be negatively affected by increased competition from the generalists (e.g. due to nectar-robbing of long-tubed flowers) after oilseed rape flowering has ceased. We expected that the increased abundance of short-tongued pollinators and reduced abundance of long-tongued bumble bees in landscapes with a high proportion of oilseed rape would impact the pollination of later flowering wild plant species. In addition, we expected contrasting effects on plants pollinated by short-tongued pollinators and those pollinated by long-tongued bumble bees. We predicted that semi-natural grasslands, which provide insects with alternative floral resources, would reduce both negative and positive effects on pollination by mitigating competition between pollinators.In 16 semi-natural grasslands, surrounded by agricultural landscapes, with a variation in both the proportion of oilseed rape and the proportion of semi-natural grassland within 1 km, we studied reproductive output in two species of potted plants with different pollination strategies: the woodland strawberry (Fragaria vesca) and red clover (Trifolium pratense). The first species is mainly pollinated by short-tongued pollinators, e.g. hoverflies and solitary bees, and the latter by long-tongued bumble bees. Both species flowered after oilseed rape.Strawberry weight was higher in landscapes with a high proportion of oilseed rape, but only in landscapes with a low proportion of semi-natural grassland. The proportion of developed achenes was also positively related to the proportion of oilseed rape, but only during the latest flowering period. In contrast, red clover seed set was unrelated to the proportion of oilseed rape. Whereas the discrepancy between the two strawberry measurements calls for further research, this study suggests that oilseed rape can affect later flowering plants and that the impact differs among species.     

Effects of site and plant species on rhizosphere community structure as revealed by molecular analysis of microbial guilds

The bacterial and fungal rhizosphere communities of strawberry (Fragaria ananassa Duch.) and oilseed rape (Brassica napus L.) were analysed using molecular fingerprints. We aimed to determine to what extent the structure of different microbial groups in the rhizosphere is influenced by plant species and sampling site. Total community DNA was extracted from bulk and rhizosphere soil taken from three sites in Germany in two consecutive years. Bacterial, fungal and group-specific (Alphaproteobacteria, Betaproteobacteria and Actinobacteria) primers were used to PCR-amplify 16S rRNA and 18S rRNA gene fragments from community DNA prior to denaturing gradient gel electrophoresis (DGGE) analysis. Bacterial fingerprints of soil DNA revealed a high number of equally abundant faint bands, while rhizosphere fingerprints displayed a higher proportion of dominant bands and reduced richness, suggesting selection of bacterial populations in this environment. Plant specificity was detected in the rhizosphere by bacterial and group-specific DGGE profiles. Different bulk soil community fingerprints were revealed for each sampling site. The plant species was a determinant factor in shaping similar actinobacterial communities in the strawberry rhizosphere from different sites in both years. Higher heterogeneity of DGGE profiles within soil and rhizosphere replicates was observed for the fungi. Plant-specific composition of fungal communities in the rhizosphere could also be detected, but not in all cases. Cloning and sequencing of 16S rRNA gene fragments obtained from dominant DGGE bands detected in the bacterial profiles of the Rostock site revealed that Streptomyces sp. and Rhizobium sp. were among the dominant ribotypes in the strawberry rhizosphere, while sequences from Arthrobacter sp. corresponded to dominant bands from oilseed rape bacterial fingerprints.     

Effects of crop plants on abundance of Pochonia chlamydosporia and other fungal parasites of root‐knot and potato cyst nematodes

The effects of a host plant on reproduction/abundance of fungal populations in relation to soil nutrients released by plants in the rhizosphere were studied. Abundance in the soil and potato rhizosphere of the fungi Paecilomyces lilacinus, Monographella cucumerina (CABI 380408) and Pochonia chlamydosporia var. chlamydosporia (Pc280, potato cyst nematode biotype) and P. chlamydosporia var. catenulata (Pc392, root‐knot nematode biotype) were assessed. The different ability of break crops (oilseed rape, sugarbeet and wheat) in the potato rotation to support Pa. lilacinus, Pochonia isolates Pc280 and Pc392 and abundance of the latter two isolates in soil and rhizosphere of potato plants infected with Meloidogyne incognita were also studied. Potato chits and crop seedlings were planted into boiling tubes containing 5000 chlamydospores or conidia g^?1 in acid washed sand (pH 6) and kept in a growth chamber at 20°C, and 16 h of light for up to 9 weeks. The abundance of the fungi in sand (fallow) differed significantly between fungal species, being in general less abundant in the absence than in the presence of the plant, although there was no interaction between plant species and fungal isolate. There was evidence of a different response to Me. incognita for Pc392 than for Pc280 but there was no significant effect of the presence of the nematode on the rate of increase of the fungus.     

Rhizosphere microbial community and its response to plant species and soil history

The plant rhizosphere is a dynamic environment in which many parameters may influence the population structure, diversity and activity of the microbial community. Two important factors determining the structure of microbial community present in the vicinity of plant roots are plant species and soil type. In the present study we assessed the structure of microbial communities in response to four plant species (i.e. maize (Zea mays L.), oat (Avena sativa L.), barley (Hordeum vulgare L.) and commercial grass mix) planted in soil with different land use history (i.e. arable land under crop rotation, maize monoculture and permanent grassland). Both factors, plant species and land use history, showed clear effects on microbial community and diversity as determined by PCR-DGGE fingerprinting with universal and group-specific bacterial primers. Moreover, we explored the rhizosphere effect of these plant species on the abundance of bacterial antagonists of the potato pathogen Rhizoctonia solani AG3. The data showed that the abundance and taxonomic composition of antagonists differed clearly between the different plants. The highest percentages of antagonists were found in maize and grass rhizosphere. When antagonistic Pseudomonas populations were compared, the highest, abundance and diversity of antagonists were detected in barley and oat rhizospheres, as compared to maize and grass rhizosphere. The results obtained in our study demonstrate clearly that plant species and soil type are two important factors affecting the structure of total bacterial, Pseudomonas and Bacillus community.     

Effects of genetically modified potatoes with increased zeaxanthin content on the abundance and diversity of rhizobacteria with in vitro antagonistic activity do not exceed natural variability among cultivars

To assess potential effects of genetically modified (GM) potatoes on the abundance and diversity of rhizobacteria with in vitro antagonistic activity in relation to natural variability among cultivars, two GM potato lines accumulating the carotenoid zeaxanthin in their tubers, the parental cultivar and four additional commercial cultivars were planted at two field sites in Germany. Rhizosphere samples were taken at three developmental stages of the plants. A total of 3,985 bacteria isolated from the rhizosphere were screened for their in vitro antagonistic activity towards Rhizoctonia solani, Verticillium dahliae and Phytophthora infestans using a dual-culture assay. Genotypic characterisation, 16S rRNA gene sequencing and antifungal metabolite analysis was performed to characterize the 595 antagonists obtained. The 16S rRNA gene-based identification of in vitro antagonists revealed strong site-dependent differences in their taxonomic composition. This study showed that the site was the overriding factor determining the proportion and diversity of antagonists from the rhizosphere of potato while the effect of the genetic modification on the proportion of antagonists obtained did not exceed natural variability among the five commercial cultivars tested.     

Cultivation-independent analysis of Pseudomonas species in soil and in the rhizosphere of field-grown Verticillium dahliae host plants

Despite their importance for rhizosphere functioning, rhizobacterial Pseudomonas spp. have been mainly studied in a cultivation-based manner. In this study a cultivation-independent method was used to determine to what extent the factors plant species, sampling site and year-to-year variation influence Pseudomonas community structure in bulk soil and in the rhizosphere of two Verticillium dahliae host plants, oilseed rape and strawberry. Community DNA was extracted from bulk and rhizosphere soil samples of flowering plants collected at three different sites in Germany in two consecutive years. Pseudomonas community structure and diversity were assessed using a polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) system to fingerprint Pseudomonas-specific 16S rRNA gene fragments amplified from community DNA. Dominant and differentiating DGGE bands were excised from the gels, cloned and sequenced. The factors sampling site, plant species and year-to-year variation were shown to significantly influence the community structure of Pseudomonas in rhizosphere soils. The composition of Pseudomonas 16S rRNA gene fragments in the rhizosphere differed from that in the adjacent bulk soil and the rhizosphere effect tended to be plant-specific. The clone sequences of most dominant bands analysed belonged to the Pseudomonas fluorescens lineage and showed closest similarity to culturable Pseudomonas known for displaying antifungal properties. This report provides a better understanding of how different factors drive Pseudomonas community structure and diversity in bulk and rhizosphere soils.     

Diversity and biocontrol potential of endophytic fungi in Brassica napus

This study was conducted to isolate endophytic fungi from oilseed rape (Brassica napus), to identify the fungal endophytes based on morphology and ITS (ITS1-5.8S rDNA-ITS2) sequences, and to evaluate their efficacy in suppression of the plant pathogenic fungi Sclerotinia sclerotiorum and Botrytis cinerea. Selected endophytic fungal isolates were further tested for promoting growth of oilseed rape in potting experiments. A total of 97 endophytic fungal isolates were obtained from roots (35), stems (49) and leaves (13) of B. napus. Forty fungal species were identified and most species (80%) belong to Ascomycota. The species composition is highly diversified with Simpson’s diversity index reaching 0.959. Alternaria alternata is the dominant species accounting for 12.4% of the isolates. Twenty-four isolates exhibited antifungal activity against S. sclerotiorum in dual cultures on potato dextrose agar forming inhibition zones of 3–17 mm in width. The culture filtrates of Aspergillus flavipes CanS-34A, Chaetomium globosum CanS-73, Clonostachys rosea CanS-43 and Leptosphaeria biglobosa CanS-51 in potato dextrose broth exhibited consistent and effective suppression of oilseed rape leaf blight caused by S. sclerotiorum. Fusarium oxysporum CanR-46 was detected capable of production of volatile organic compounds highly inhibitory to S. sclerotiorum and B. cinerea. Moreover, A. alternata CanL-18, Fusarium tricinctum CanR-70 and CanR-71r, and L. biglobosa CanS-51 exhibited growth-promoting effects on oilseed rape. These results suggest that B. napus harbors diversified endophytic fungi, from which potential biocontrol agents against S. sclerotiorum and B. cinerea, and for promoting growth of B. napus can be screened.     

Population Dynamics of Soil Pseudomonads in the Rhizosphere of Potato (Solanum tuberosum L.)

Rhizosphere population dynamics of seven Pseudomonas fluorescens and Pseudomonas putida strains isolated from rhizospheres of various agricultural plants were studied on potato (Solanum tuberosum L.) in field soil under controlled environmental conditions. Rhizosphere populations of two strains (B10 and B4) were quantitatively related to initial seed piece inoculum levels when plants were grown at −0.3 bar matric potential. At a given inoculum level, rhizosphere populations of strain B4 were consistently greater than those of strain B10. In vivo growth curves on 4-cm root tip-proximal segments indicated that both strains grew at similar rates in the potato rhizosphere, but large populations of strain B10 were not maintained at 24°C after 7 h, whereas those of strain B4 were maintained for at least 40 h. Although both strains grew more rapidly in the rhizosphere at 24°C than at 12°C, their rhizosphere populations after seed piece inoculation were generally greater at 12 or 18°C, indicating that in vivo growth did not solely determine rhizosphere populations in these studies. In vitro osmotolerance of seven Pseudomonas strains (including strains B4 and B10) was correlated with their abilities to establish stable populations in the rhizosphere of potato. Stability of rhizosphere populations of the Pseudomonas strains studied here was maximized at low (i.e., 12°C) soil temperatures. These results indicate that Pseudomonas strains differ in their capacity to maintain stable rhizosphere populations in association with potato. This capacity, distinct from the ability to grow in the rhizosphere, may limit the establishment of rhizosphere populations under some environmental conditions.     

基于高通量测序的福建北部马铃薯晚疫病株根际土壤细菌群落分析

[背景]马铃薯晚疫病是一种由致病疫霉[Phytophthora infestans(Mont.)de Bary]引起的毁灭性病害,当环境条件适宜时,残留在土壤中的病原菌会侵染马铃薯植株导致病害的发生.[目的]明确健康马铃薯植株与发病植株的根际土壤细菌结构与多样性.[方法]采集马铃薯晚疫病发病地的健康植株根际土壤(M2J...     

An overview of rhizosphere processes related with plant nutrition in major cropping systems in China

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.