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1.
Nineteen monoconidial isolates (referred to as clones) of Trichoderma from different species aggregates, one isolate of Gliocladium virens, and one isolate of an Acrostalagmus sp. (that was naturally associated with sclerotia of Sclerotinia spp and Macrophomina phaseolina) were tested. They were incubated in controlled conditions, in sterile soil, with sclerotia of Corticium rolfsii, Sclerotinia minor, or S. sclerotiorum. At the end of appropriate periods of incubation (respectively 26, 20 and 8 days), the sclerotia were retrieved from soil and checked for invasion by the antagonist. Important differences between the parasitic ability of Trichoderma clones were noted. Clones from at least three different species (T. aureoviride, T. hamatum, T. harzianum) exhibited a high antagonistic activity. Activity of the G. virens isolate was at the same level as the best clones of Trichoderma, whereas no parasitic tendencies were found in the isolate of Acrostalagmus sp., thus confirming previous results.A rather good correlation was found between the capacity of the clones for attacking C. rolfsii sclerotia and their ability to parasitize both Sclerotinia.In conclusion, it is proposed that a screening with only one of the sclerotial species would give clones efficient against all three, and possibly against related sclerotial types. 相似文献
2.
Ten isolates of Trichoderma spp were examined for their ability to antagonize growth and to parasitize mycelium of Sclerotium rolfsii (Sr-1) on agar media, to inhibit germination of sclerotia of S. rolfsii on natural soil plates and to sporulate on the sclerotia, and to protect bean seedlings against the pathogen in the greenhouse. A high negative correlation (r = ?0.844) was observed between plant stand in the greenhouse and sclerotial germination on soil plates but not with antagonism on agar plates. Three isolates of T. harzianum (Th-7, Th-20, WT-6) and one of T. hamatum (TRI-4) were especially effective in reducing sclerotial germination and controlling disease in the greenhouse. Three isolates of Trichoderma spp (WT-6, TMP, and TRI-4), effective in reducing sclerotial germination of isolate Sr-1, also prevented sclerotial germination in four out of five additional S. rolfsii isolates studied. 相似文献
3.
Organic residues provide the fundamental energy supply supporting soil fungal communities. Provision of adequate energy is required for soil microbial communities to adapt and function in the presence of ecological stress, such as copper (Cu) contamination. However, contamination can also lead to decreased ecological fitness of microorganisms, limiting their ability to access substrates. Thus, complex interactions exist between substrates, metals, energy supply/accessibility, fungal communities and their processes, and these have implications for ecosystem processes. We investigated the interaction between energy resources and Cu tolerance on soil fungal communities, including Fusarium and Trichoderma (model disease causing and beneficial genera). Using quantitative PCR and DGGE fingerprinting, the effects of increasing soil Cu levels (0 to >3000 mg Cu kg−1 soil) on size and structure of soil fungal communities were tested under basal and plant-residue (medic; Medicago trunculata) added conditions. The interaction between increasing soil Cu levels and the addition of plant resources on fungal community structure was tested using multivariate analysis. The relative size (DNA copies per unit of soil DNA) of soil fungal communities, including Trichoderma and Fusarium, significantly (P < 0.05) increased (94% and 32% respectively) with addition of medic to soil. In medic-applied samples, the bacterial to fungal ratio decreased, demonstrating the selective influence of the cellulose-rich substrate on the fungal community. Under the high nutrient conditions fungal DNA increased as a fraction of the total soil DNA, demonstrating the tolerance of fungi to Cu (relative to other microbiota) given adequate energy resources. Copper had no impact on the abundance of Fusarium or Trichoderma, but significantly affected community structure (PERMANOVA; P < 0.05). With increasing Cu, species selection and replacement could be observed, particularly in soils where medic had been included. Plant residue addition itself was a highly selective factor affecting the structure of communities of Trichoderma and Fusarium (P < 0.05). The effects of increasing Cu could be seen in both medic and basal soils for Trichoderma, but only in the basal treatments for soil Fusarium. This was due to very low dispersion in Fusarium community structure in the medic-added treatment (PERMDISP; P < 0.05). The results show the interactive influence of organic matter inputs and heavy metal contamination on size and structure of soil fungal communities. The data show that species selection and replacement is an important mechanism for community adaptation to increasing levels of soil Cu, and this mechanism can be influenced by addition of resources to the soil. 相似文献
4.
Some members of the fungal genus Trichoderma are able to colonize and destroy sclerotia, the thick-walled resting structures of the soilborne plant pathogenic fungus Sclerotinia sclerotiorum, thus providing a potential means of biological disease control. However, current methods to detect and quantify colonization of sclerotia are labor-intensive, and generally qualitative rather than quantitative in nature. Our objective was to develop quantitative real-time PCR (polymerase chain reaction) methods to detect and measure colonization of sclerotia by Trichoderma spp. Specific PCR primer/probe sets were developed for Trichoderma spp. and for S. sclerotiorum. A total of 180 ITS1 (internal transcribed spacer) and ITS2 sequences from different species in the genus Trichoderma were aligned, and consensus sequences were determined. Six candidate primer sets were based on conserved regions of the consensus sequence, and the specificity of each nucleotide sequence was examined using BLAST (Basic Local Alignment Search Tool; NCBI) software. Each candidate primer set was tested on genomic DNA of T. harzianum strain ThzID1-M3, as well as six different Trichoderma isolates from soil, and on genomic DNA of S. sclerotiorum. The optimum primer/probe set selected, TGP4, successfully amplified genomic DNA of all Trichoderma isolates tested, and showed high precision and reproducibility over a linear range of eight orders of magnitude, from 85 ng to 8.5 fg of T. harzianum genomic DNA. TGP4 did not amplify S. sclerotiorum DNA. A specific PCR primer/probe set (TMSCL2) was developed for S. sclerotiorum, based on the calmodulin gene sequence. TMSCL2 did not amplify Trichoderma DNA. Quantitative real-time PCR with the primers then was evaluated in experiments to test differential effects of two soil moisture levels (−50 kPa, −1000 kPa matric potential) on biocontrol of S. sclerotiorum by indigenous Trichoderma spp. Periodically over 40 days, Trichoderma and S. sclerotiorum DNA in sclerotia were quantified by PCR with appropriate primers. Over 90% of the sclerotia were colonized by indigenous Trichoderma spp. at −1000 kPa, over the 40-day period, compared to only 60% at −50 kPa. In addition to determining incidence of colonization, the PCR method allowed measurement of the extent of sclerotial colonization, which also was significantly greater in the drier soil. Quantitative real-time PCR with the TGP4 primer/probe set provides a sensitive detection and measurement tool to evaluate colonization of sclerotia by Trichoderma spp. 相似文献
5.
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. 相似文献
6.
Louise M. Nelson 《Soil biology & biochemistry》1982,14(3):219-222
Fifty bacterial isolates from a parathion-treated soil (Gilat, Israel) were tested for their ability to hydrolyze the organophosphorus insecticide, parathion in peptone-yeast extract medium. After 5 days 33 isolates had hydrolyzed at least a portion of the added parathion. Eight of these isolates hydrolyzed 75% of the added parathion in 5 days and appeared to be Bacillus strains. Ten of these 33 isolates had hydrolyzed all of the parathion after 5 days and appeared to be Arthrohacter strains. One isolate from each group was tested further. During the logarithmic phase of growth, Bacillus sp., isolate 10, hydrolyzed less than 10% of the parathion added to peptone-yeast extract medium and was not active in parathion hydrolysis when inoculated into sterilized, parathion-treated soil. Arthrobacter sp., isolate 6, hydrolyzed parathion rapidly in peptone-yeast extract medium and in sterilized, parathion-treated soil. It used parathion or its hydrolysis product, p-nitrophenol, as sole carbon source. The parathion hydrolyzing enzyme appeared to be constitutive in isolate 6. Single applications of p-nitrophenol at concentrations greater than 1 mM inhibited growth but successive additions of smaller amounts permitted growth to continue. 相似文献
7.
《Applied soil ecology》2007,35(1):237-246
Effectiveness of Trichoderma strains for biocontrol of soilborne pathogens requires an improved understanding of soil and root ecology of this fungus. We compared the population dynamics of Trichoderma hamatum strain T382 (T382) and indigenous Trichoderma spp. in soil and on roots in different strawberry production systems. Strawberry transplants, either amended or not-amended with Trichoderma biocontrol strains, were planted in field soil left untreated or treated with soil fumigant, compost, and compost-amended with T382. Soil and root samples were taken between October and June of two production seasons (2002-03 and 2003-04), and Trichoderma populations were assessed by plating soil dilutions and root pieces onto selective medium. Identity of T382 was confirmed using strain-specific primers. T382 became established and maintained a stable population of 103 cfu/g soil throughout the growing season when added to field soil in amended compost, but T382 was rarely isolated from strawberry roots. Populations of indigenous Trichoderma spp. were up to 60-fold greater in fumigated soil than in any other soil treatment. Indigenous Trichoderma spp. were isolated from a greater proportion (20–50%) of roots in fumigated soil than from roots in the other treatments (0–20%). Transplant treatments did not significantly affect Trichoderma populations on roots or in soil during field production. This study showed that compost may be used as a substrate to establish and promote survival of Trichoderma in field soil, and illustrates how soil manipulation can affect population dynamics of indigenous Trichoderma spp. on roots and in soil. 相似文献
8.
Antoine Affokpon Danny L. Coyne Rufin Dossou Agbèdè Jozef Coosemans 《Soil biology & biochemistry》2011,43(3):600-608
Seventeen isolates of the free-living soil fungus Trichoderma spp., collected from Meloidogyne spp. infested vegetable fields and infected roots in Benin, were screened for their rhizosphere competence and antagonistic potential against root-knot nematodes, Meloidogyne incognita, in greenhouse pot experiments on tomato. The five isolates expressing greatest reproductive ability and nematode suppression in pots were further assessed in a typical double-cropping system of tomato and carrot in the field in Benin. All seventeen isolates were re-isolated from both soil and roots at eight weeks after application, with no apparent crop growth penalty. In pots, a number of isolates provided significant nematode control compared with untreated controls. Field assessment demonstrated significant inhibition of nematode reproduction, suppression of root galling and an increase of tomato yield compared with the non-fungal control treatments. Trichoderma asperellum T-16 suppressed second stage juvenile (J2) densities in roots by up to 80%; Trichoderma brevicompactum T-3 suppressed egg production by as much as 86%. Tomato yields were improved by over 30% following the application of these biocontrol agents, especially T. asperellum T-16. Although no significant effects were observed on carrot galling and yield, soil J2 densities were suppressed in treated plots, by as much as 94% (T. asperellum T-12), compared with the non-fungal controls. This study provides the first information on the potential of West-African Trichoderma spp. isolates for use against root-knot nematodes in vegetable production systems. The results are highly encouraging, demonstrating their strong potential as an alternative and complementary crop protection component. 相似文献
9.
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. 相似文献
10.
Katsuki Adachi Makoto Nakatani Hideyuki Mochida 《Soil Science and Plant Nutrition》2013,59(6):889-895
Abstract The population density of endophytic bacteria in the stem of field-grown sweet potato cultivars (Beniotome [BO], Koganesengan [KS], and Shiroyutaka [SYD in Miyakonojo, Miyazaki, Japan, ranged from 102 to 104 cells g?1 fresh weight sample using a semi-solid nitrogen-free medium. Eleven strains were isolated from the stems and two isolates, BO-1 and BO-5, showed a positive reaction in the acetylene reduction activity (ARA) test. BO-1 and BO-5 were isolated from cv. Beniotome in September 1999 and 2000, respectively. Morpho-physiological characterization of these isolates revealed that BO-1 and BO-5 showed a similar colony color in potato sucrose agar slants, produced bubbles in a modified semi-solid medium, acidified the medium, and displayed similar characteristics using the API 20NE rapid diagnostic kit. Partial sequence analysis of 16S rRNA from BO-1 revealed a 100% similarity (491 bp) to that of Klebsiella oxytoca. The other 9 isolates showed a negative reaction in the ARA test, slightly acidified or did not acidify the medium. Partial sequence analysis of the 16S rRNA revealed that the isolate SY-2 corresponded to Methylobacterium sp. (99.3% similarity for 1,241 bp), BO-3 to Pantoea agglomerans (99.1% similarity for 469 bp), and BO-8 to Sphingomonas sanguinis (98.8% similarity for 419 bp). 相似文献
11.
E.E. Nelson 《Soil biology & biochemistry》1976,8(1):51-53
Poria weirii (Murr.) Murr. (an important root-infecting fungus of conifers in western North America) grown in alder stem sections and buried in soil at 15°C survived better when urea was not added to the soil. Survival over a 32 week period was inversely related to rate of urea applied. Fungus populations were greatest at 4 weeks after which numbers of Trichoderma began to increase. This corresponded with decreased survival of P. weirii; Trichoderma was the fungus isolated almost exclusively from alder sections when P. weirii was not. Increasing soil populations of actinomycetes with time may have had some effect on survival as well. 相似文献
12.
The prevalence of antibiotic production loci in soil is a key issue of current research aimed to unravel the mechanisms underlying the suppressiveness of soil to plant pathogens. Pyrrolnitrin (PRN) is a key antibiotic involved in the suppression of a range of phytopathogenic fungi. Therefore, field soils from different agricultural regimes, including permanent grassland, arable land under common agricultural rotation and arable land under maize monoculture, were investigated in respect of the prevalence of pyrrolnitrin biosynthetic loci. Primers for detection of the prnD gene were used for initial PCR/hybridisation-based assessments. By this method, evidence was obtained for the contention that PRN production loci were most prevalent in grasslands, however, robust quantitative data were not achieved.To quantify the prevalence of PRN biosynthetic loci, we designed a TaqMan PCR system based on the prnD gene for the real-time quantitative detection of this production locus in soil. The system was found to be specific for prnD sequences from Pseudomonas, Serratia and Burkholderia species. Using pure culture DNA, the prnD gene was detectable down to a level of 60 fg, or approximately 10 gene copies, per amplification reaction. Application of the system to soil DNA spiked with different levels of the target DNA indicated that, in a soil DNA background, specific amplification could be obtained to about the same level of sensitivity.Field soil samples obtained from the different agricultural regimes were then screened for the prevalence of prnD with the real-time PCR system. The quantitative data obtained suggested a strongly enhanced presence of prnD genes in grassland or grassland-derived plots, as compared to the prevalence of this biosynthetic locus in the arable land plots. The implications of these findings are placed in the context of the suppressiveness of soil to phytopathogens, notably Rhizoctonia solani AG3. 相似文献
13.
Rhizoctonia solani causes worldwide losses in numerous crops. Sclerotia of R. solani remain viable for several years in soil and are an important source of primary infection. In this study the effect of soil incorporation of Kraft pine lignin, a side product of the paper industry, on viability of R. solani AG1-1B sclerotia was investigated. The efficacy of lignin was assessed in a sandy loam (Oppuurs) and a silt loam soil (Leest) collected from commercial fields in Belgium. Evaluating sclerotial viability after 4 weeks incubation in the two soils amended with 1% (w/w) Kraft pine lignin demonstrated a soil-dependent effect. In Leest soil the addition of lignin resulted in a significantly reduced sclerotial viability, together with an increased mycoparasitism by Trichoderma spp.; in Oppuurs soil, on the other hand, only a slight and insignificant reduction in sclerotial viability was observed. Based on phospholipid fatty acid analysis, different changes in microbial community structure upon lignin amendment were detected in the two soils. Both amended soils showed a significant increase in Gram negative bacteria. In Leest soil this increase was accompanied with a significantly higher increase in fungi and actinomycetes compared with Oppuurs soil. In addition, Kraft pine lignin resulted in both soils in a small but significant increase in manganese peroxidase activity and this increase tended to be higher in Leest soil. Manganese peroxidase produced by lignin-degrading basidiomycetes has previously been shown to degrade melanin, which protects the sclerotia against biotic and abiotic stress. We hypothesize that lignin-degrading fungi increased the susceptibility of the sclerotia to sclerotial antagonists such as Trichoderma, Gram negative bacteria and actinomycetes. Clearly, the effect observed here did not rely on the stimulation of one microbial group, but is the result of an interaction of different groups. 相似文献
14.
Anita Juen 《Soil biology & biochemistry》2006,38(7):1872-1879
Polymerase chain reaction (PCR) can be used to detect prey within the gut contents of predators and allows specific trophic interactions to be studied among soil-dwelling invertebrates which cannot be examined by other approaches. PCR-inhibitory substances, however, are commonly found in DNA prepared from soil organisms or from biological material contaminated with soil. This can lead to false-negative results and the risk of not detecting trophic connections or of underestimating predation rates in field studies. In the present study, we developed mitochondrial DNA markers to detect Amphimallon solstitiale (Coleoptera: Scarabaeidae) in the gut contents of invertebrate predators. Larvae of A. solstitiale can cause serious damage in grasslands, field crops, and forests by feeding on roots. Adequate methodologies to study predation on these pests are lacking, and their invertebrate predator guild is, therefore, barely known. To test the new molecular markers for prey detection, larvae and eggs of A. solstitiale were fed to Poecilus versicolor larvae (Coleoptera: Carabidae), which are abundant below-ground predators in grassland ecosystems. Unfortunately, even when specific DNA extraction and purification methods were used, DNA extracts from predators were of poor quality and not amplifiable by PCR; this yielded false-negative results and a dramatically lower prey-detection rate. We overcame PCR-inhibition by applying ?1.28 μg μl−1 bovine serum albumin to the PCR reaction mix. This enabled us to detect A. solstitiale DNA within fed carabid larvae up to 48 and 40 h post-feeding for 127 and 463 bp sized DNA fragments, respectively. When single A. solstitiale eggs were consumed by the carabid larvae, predation could be verified in 100% of the predators within the first 8 h of digestion; some carabid larvae even tested positive 32 h after feeding. Moreover, by multiplexing primers targeting both prey and predator, we were able to simultaneously screen for prey consumption and check for co-purified PCR inhibitors. Sensitivity in prey detection was not reduced compared to singleplex PCR. We recommend the multiplex approach because it considerably reduces time and costs compared to singleplex assays. We also show that multiplex PCR not only detects specific prey, but also can identify the predator itself. This allows the identification of taxa which are difficult or not identifiable based on morphological characters, such as soil-dwelling predatory beetle larvae. 相似文献
15.
The genetic diversity of Aspergillus flavus populations isolated from the peanut-cropped soils in the peanut-growing region at Cordoba Province was evaluated by analysis of vegetative compatibility group (VCG). VCGs were determined through complementation assays between nitrate-nonutilizing (NNO) mutants. Fifty-six VCGs were identified from 100 isolates. Twenty-five VCGs contained two or more isolates and 31 VCGs contained only a single isolate. In general, there were significant differences among VCGs in aflatoxin and CPA production. One VCG group included a single atoxigenic strain since it was neither aflatoxin nor cyclopiazonic acid producer. This isolate could be useful as a biological control agent, since it was unable to form a stable heterokaryon in the complementation test with the other isolates. Seven A. flavus isolated from soil were atypical because they simultaneously produced aflatoxins B, G and CPA. 相似文献
16.
Two fungal strains producing ligninolytic enzymes and having the potential to decolorize distillery effluent were isolated from the soil of a distillery effluent contaminated site. DNA was isolated from the pure cultures of these fungi and polymerase chain reaction (PCR) amplification of their internal transcribed spacer (ITS) region of nuclear ribosomal DNA was carried out. Further, the DNA was sequenced and the comparison of generated sequence with database led to their identification as Penicillium pinophilum TERI DB1 and Alternaria gaisen TERI DB6 respectively. These two isolates along with one isolate of Pleurotus florida EM 1303 were assessed for their ligninolytic enzyme activity in culture filtrate as well as after solid state fermentation on two substrates wheat straw and corncob powder. Ergosterol was measured to assess the growth of fungi on solid media. Both P. pinophilum TERI DB1 and A. gaisen TERI DB6 were found to produce laccase, manganese-dependent peroxidases (MnP) and lignin peroxidases (LiP). The immobilized fungal biomass was then used for decolorization of the post biomethanated wastewater from the distillery. Reduction in color up to the magnitude of 86, 50 and 47% was observed with P. florida, P. pinophilum and A. gaisen respectively. 相似文献
17.
Olivier Couillerot Marie-Lara Bouffaud Ezékiel Baudoin Daniel Muller Jesus Caballero-Mellado 《Soil biology & biochemistry》2010,42(12):2298-2305
Azospirillum lipoferum CRT1 is a promising phytostimulatory PGPR for maize, whose effect on the plant is cell density-dependent. A nested PCR method is available for detection of the strain but does not allow quantification. The objective was to develop a real-time PCR method for quantification of A. lipoferum CRT1 in the rhizosphere of maize seedlings. Primers were designed based on a strain-specific RFLP marker, and their specificity was verified under qualitative and quantitative PCR conditions based on successful CRT1 amplification and absence of cross-reaction with genomic DNA from various rhizosphere strains. Real-time PCR conditions were then optimized using DNA from inoculated or non-inoculated maize rhizosphere samples. The detection limit was 60 fg DNA (corresponding to 19 cells) with pure cultures and 4 × 104 CFU equivalents g−1 lyophilized sample consisting of mixture of rhizosphere soil and roots. Inoculant quantification was effective down to 104 CFU equivalents g−1. Assessment of CRT1 rhizosphere levels in a field trial was in accordance with estimates from semi-quantitative PCR targeting another locus. This real-time PCR method, which is now available for direct rhizosphere monitoring of A. lipoferum CRT1 in greenhouse and field experiments, could be used as a reference for developing quantification tools for other Azospirillum inoculants. 相似文献
18.
Fungal communities in soils of Nigerian maize fields were examined to determine distributions of aflatoxin-producing fungi and to identify endemic atoxigenic strains of potential value as biological control agents for limiting aflatoxin contamination in West African crops. Over 1000 isolates belonging to Aspergillus section Flavi were collected from soil of 55 Nigerian maize fields located in three agroecological zones by dilution plating onto modified Rose Bengal agar. The most common member of Aspergillus section Flavi (85% of isolates) was the A. flavus L-strain followed by the unnamed taxon known as strain SBG (8%), A. tamarii (6%) and A. parasiticus (1%). Highest incidence of SBG was in Zaria district, and lowest was in Ogbomosho and Ado-Ekiti districts. Only 44% of 492 A. flavus isolates produced aflatoxins in liquid fermentation (limit of detection 5 ng g−1). Thirty-two percent of the A. flavus isolates produced >1 μg g−1 total aflatoxins but no A. flavus isolate produced G aflatoxins. When the agroecological zones were compared, significantly (P < 0.05) greater proportions of aflatoxigenic A. flavus isolates were found in the Northern Guinea Savannah (61%) than in Southern Guinea Savannah (31%). The Derived Savannah was intermediate between the other two agroecological zones. Each of the regions had atoxigenic strains of potential value as biological control agents. All SBG and A. parasiticus isolates produced both B and G aflatoxins and greater than 300 μg g−1 total aflatoxins. SBG and A. parasiticus isolates were the greatest contributors to the aflatoxin-producing potential of fungal communities in regions where these isolates occurred. 相似文献
19.
Shaili Srivastava 《Soil biology & biochemistry》2006,38(7):1904-1911
Aspergillus niger isolated from soil of leather tanning effluent had higher activity to remove chromium then the other fungal isolates. The potency of A. niger was evaluated in shake flask culture by absorption of chromium at pH 6, temperature 30 °C. The toxicity of chromium evaluated in petriplates and soil microcosm seed bioassay test had indicated increase in toxicity with the higher concentration of chromate. A. niger introduced in soil microcosm (40% moisture content) with different concentration of chromate (250, 500, 1000, 1500 and 2000 ppm) removed more than 70% chromium in soil contaminated by 250 and 500 ppm of chromate. However, chromium-contaminated soil (2000 ppm of potassium chromate) mixed with compost (5% and 10%) significantly removed chromium in presence of fungus, A. niger. The results of chromate toxicity in the wheat plants revealed that the peroxidases was induced due to increase of metal stress which was reversed in soil microcosm amended with compost. 相似文献
20.
The effects of forest fires on the soil mycotlora were investigated in a Pinus contorta forest in Alberta, where it was found that species of Trichoderma and Penicillium were reduced in the burned plot, whereas Gelasinospora sp occurred only in the burned plot: Cylindrocarpon destructans appeared not to be affected by fire.The response of fungi to aqueous extracts of burned and unburned litter, measured as linear growth on agar, showed that, of the isolates tested, all but C. destructans were inhibited by the burned litter extract; C. destructans grew better on the burned litter extract. An examination of spore germination rates and growth in liquid culture showed that Trichoderma polysporum and Penicillium janthinellum were both inhibited by burned litter extracts whereas C. destructans was not. Gelasinospora sp did not grow in liquid culture, nor did it produce spores after being kept in culture for some time.It was concluded that species of Trichoderma and Penicillium were killed by the heat of the fire, and subsequently unable to rccolonize the upper layers of the soil, due to an inhibition of spore germination and growth by the chemical products of burning. C. destructans on the other hand may have been able to recolonize quickly as it appeared to be stimulated in its linear growth rate by the chemical products of burning, and its spore germination rate was only marginally lowered. The occurrence of Gelasinospora sp following fire is possibly explained by its extremely rapid growth rate, and the possibility of its ascospores being more able to withstand high temperatures in the soil.In the light of recent reports, indicating that some species of Trichoderma and Penicillium are actively antagonistic to other fungi, it is suggested that their absence after fire, in the area studied, may permit a high inoculum of C. destructans to develop in the soil, which could possibly result in a high incidence of disease in developing pine seedlings 相似文献