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1.
In Cameroon, andosols are suspected to be suppressive to cocoyam (Xanthosoma sagittifolium) root rot disease (CRRD) caused by the Oomycete pathogen Pythium myriotylum. To determine factors involved in disease suppressiveness, andosols were studied in comparison to ferralsols known to be disease-conducive. Soil samples were collected from six sites of which three were in andosols around Mount Cameroon (Boteva, Njonji, and Ekona) and the three others in ferralsols (Bakoa, Lapkwang, and Nko’o canane). Greenhouse plant experiments were used to assess soil suppressiveness. Soils were artificially infested with two levels of P. myriotylum inoculum (100 and 300 mycelia strands g−1 soil) prior to planting cocoyam. Disease severity was significantly higher in ferralsols than in andosols. Andosols partly lost their suppressiveness as a result of autoclaving and could recover suppressiveness following recolonisation by their original microflora. Soil microbial groups implicated in the disease suppression were investigated by assessing the effect of fungicide, bactericide, and pasteurisation on andosol suppressiveness. Andosols suppressiveness was significantly reduced following pasteurisation and treatment with fungicide and bactericide. The possible influence of microbial biomass on andosol suppressiveness was investigated by comparing microbial populations of suppressive andosols to those in andosols that had lost suppressiveness. A comparative analysis of suppressive and conducive soil properties was performed to identify soil variables, which may contribute to soil suppressiveness. Soil chemical analysis results showed that organic matter content was higher in andosols than in ferralsols. In addition, the content of mineral nutrients such as Ca, K, Mg and N, was higher in andosols than in ferralsols. These soil variables negatively correlated with disease severity. By contrast, sand and clay, which were higher in ferralsols than in andosols, were positively related to disease severity. This study has confirmed the suppressive nature of andosols from Mount Cameroon to CRRD. The results suggest that high organic matter content is likely mediating P. myriotylum suppression in andosols by improving soil structure, increasing soil nutrient content and microbial biomass, and sustaining microbial activity.  相似文献   

2.
Biowaste can be converted into compost by composting or by a combination of anaerobic digestion and composting. Currently, waste management systems are primarily focused on the increase of the turnover rate of waste streams whereas optimisation of product quality receives less attention. This results in low quality composts that can only be sold on bulk markets at low prices. A new market for quality compost could be potting mixes for horticultural container-grown crops to partially replace non-renewable peat and increase the disease suppressiveness of potting mixes. We report here on the effect of wetsieving biowaste prior to composting on compost quality and on disease suppressiveness against the plant pathogen Pythium ultimum of peat mixes amended with this compost. The increased organic matter and decreased salt content of the compost allow for significantly higher substitution rates of peat by compost. In this study up to 60% v/v compost peat replacement did not affect cucumber growth. However, disease suppressiveness of the potting mixes strongly increased from 31 to 94% when the compost amendment rate was increased from 20 to 60%. It was shown that general disease suppression for P. ultimum can only be effective when the basal respiration rate is sufficiently high to support microbial activity. In addition, organic matter of the compost should reach a sufficient stability level to turn from disease conducive to disease suppressive. Increasing the compost addition from 20 to 60% did not significantly affect plant yield, yield variation were due to differences in nutrient levels. It can be concluded that compost from wetsieved biowaste has high potential to replace peat in growing media for the professional market.  相似文献   

3.
Arable fields of 10 organic farms from different locations in The Netherlands were sampled in three subsequent years. The soil samples were analysed for disease suppressiveness against Rhizoctonia solani AG2.2IIIB in sugar beet, Streptomyces scabies in radish and Verticillium longisporum in oilseed rape. In addition, a variety of microbial, chemical and physical soil characteristics were assessed. All data were correlated by multiple regression and multivariate analyses with the objective to find correlations between soil suppressiveness and biotic or abiotic soil characteristics. Significant differences in soil suppressiveness were found between the fields for all three diseases. Multiple regression indicated a significant correlation between suppressiveness against Rhizoctonia and the number of antagonistic Lysobacter spp., as well as with % active fungi and bacterial diversity. Grass-clover stimulated Rhizoctonia suppression as well as the presence of antagonistic Lysobacter spp. (mainly L. antibioticus and L. gummosus) in clay soils. Streptomyces suppression correlated with the number of antagonistic Streptomyces spp., % of active fungi and bacterial population size. The presence of antagonistic Streptomyces spp. correlated with a high fungal/bacterial biomass ratio. Verticillium suppression was only measured in 2004 and 2005, due to the inconsistent suppressiveness along the years. Nevertheless, a significant correlation with pH, potential nitrogen mineralization and bacterial biomass was found. Bacterial and fungal PCR-denaturing gel electrophoresis fingerprinting of bacterial and fungal communities, in general, did not significantly correlate with disease suppression. Highly significant explanatory factors of the composition of the dominating bacterial and fungal populations were % lutum, pH, C/N quotient, biomass and growth rate of bacteria. Additionally, the % of organic matter and years of organic farming were explaining significantly the composition of the bacterial population.Thus, significant correlations between several soil characteristics and suppressiveness of different soil-borne pathogens were found. For two of the three pathogens, suppression correlated with biotic soil characteristics combined with the presence of specific bacterial antagonists. Probably the soil suppressiveness measured in the organic fields is a combined effect of general and specific disease suppression.  相似文献   

4.
Disease suppressiveness against Rhizoctonia solani AG 2-1 in cauliflower was studied in two marine clay soils with a sandy loam texture. The soils had a different cropping history. One soil had a long-term (40 years) cauliflower history and was suppressive, the other soil was conducive and came from a pear orchard not having a cauliflower crop for at least 40 years. These two soils were subjected to five successive cropping cycles with cauliflower or remaining fallow in a greenhouse experiment. Soils were inoculated with R. solani AG 2-1 only once or before every crop. Disease decline occurred in all treatments cropped with cauliflower, either because of a decreased pathogen population or increased suppressiveness of the soil. Disease suppressiveness tests indicated that the conducive soil became suppressive after five subsequent cauliflower crops inoculated each cycle with R. solani AG 2-1. Suppressiveness of all treatments was measured in a seed germination test (pre-emergence damping-off) as well as by measuring the spread of R. solani symptoms in young plants (post-emergence damping-off). Results showed that suppressiveness was significantly stimulated by the successive R. solani inoculations; presence of the cauliflower crop had less effect. Suppressiveness was of biological origin, since it disappeared after sterilization of the soil. Moreover, suppressiveness could be translocated by adding 10% suppressive soil into sterilized soil. The suppressive soil contained higher numbers of culturable filamentous actinomycetes than the conducive soil, but treatments enhancing suppressiveness did not show an increased actinomycetes population. The suppressiveness of the soil samples did also not correlate with the number of pseudomonads. Moreover, no correlation was found with the presence of different mycoparasitic fungi, i.e. Volutella spp., Gliocladium roseum, Verticillium biguttatum and Trichoderma spp. The suppressive soil contained a high percentage of bacteria with a strong in vitro inhibition of R. solani. These bacteria were identified as Lysobacter (56%), Streptomyces (23%) and Pseudomonas (21%) spp. A potential role of Lysobacter in soil suppressiveness was confirmed by quantitative PCR detection (TaqMan), since a larger Lysobacter population was present in suppressive cauliflower soil than in conducive pear orchard soil. Our experiments showed that successive cauliflower plantings can cause a decline of the damage caused by R. solani AG 2-1, and that natural disease suppressiveness was most pronounced after subsequent inoculations with the pathogen. The mode of action of the decline is not yet understood, but antagonistic Lysobacter spp. are potential key organisms.  相似文献   

5.
Compost is often reported as a substrate that is able to suppress soilborne plant pathogens, but suppression varies according to the type of compost and pathosystem. Reports often deal with a single pathogen while in reality crops are attacked by multiple plant pathogens. The goal of the present study was to evaluate the disease suppression ability of a wide range of composts for a range of plant pathogens. This study was conducted by a consortium of researchers from several European countries. Composts originated from different countries and source materials including green and yard waste, straw, bark, biowaste and municipal sewage. Suppressiveness of compost-amended (20% vol./vol.) peat-based potting soil was determined against Verticillium dahliae on eggplant, Rhizoctonia solani on cauliflower, Phytophthora nicotianae on tomato, Phytophthora cinnamomi on lupin and Cylindrocladium spathiphylli on Spathiphyllum sp., and of compost-amended loamy soil (20% vol./vol.) against R. solani on Pinus sylvestris and Fusarium oxysporum f. sp. lini on flax. From the 120 bioassays involving 18 composts and 7 pathosystems, significant disease suppression was found in 54% of the cases while only 3% of the cases showed significant disease enhancement. Pathogens were affected differently by the composts. In general, prediction of disease suppression was better when parameters derived from the compost mixes were used rather than those derived from the pure composts. Regression analyses of disease suppression of the individual pathogens with parameters of compost-amended peat-based mixes revealed the following groupings: (1) competition-sensitive: F. oxysporum and R. solani/cauliflower; (2) rhizosphere-affected: V. dahliae; (3) pH-related: P. nicotianae; and (4) specific/unknown: R. solani/pine, P. cinnamomi and C. spathiphylli. It was concluded that application of compost has in general a positive or no effect on disease suppression, and only rarely a disease stimulating effect.  相似文献   

6.
The effect of storage conditions on compost suppressiveness against fusarium wilt of melon, caused by Fusarium oxysporum f. sp. melonis (FOM) was studied in relation to the dynamics of compost microbial activity and biodegradability. For this purpose, mature suppressive compost, prepared from tomato plants and separated cow manure, was divided into four portions and stored for one year under cool/warm (12 or 28 °C) or dry/wet (15-35 or 55-65% moisture content) conditions, in four different combinations: cool-dry, warm-dry, cool-wet and warm-wet. All composts retained and even enhanced their suppressive capacity during storage, with no significant differences among them by the end of the storage period. However, significant differences were found in the dynamics of some of the measured chemical and microbial properties. The microbial activity of composts stored under wet conditions was higher than that of those stored under dry condition, which resulted in a substantial decrease in dissolved organic matter content (expressed as dissolved organic carbon; DOC) and increase in its recalcitrance to biological degradation, decrease in basal heat emission, slower response to added glucose or citric acid, and higher NO3 concentration, indicating increased nitrification under wet conditions. The DOC significantly correlated with several microbial properties as well as with compost suppressiveness of fusarium wilt of melon seedlings, and may be regarded as a most suitable general index for compost maturity. A best-subset multiple linear regression analysis revealed that the three best predictors, namely dissolved organic carbon (DOC), basal heat, and mesophilic bacterial counts, could explain as much as 83% of the total variance in compost suppressiveness. The generally agreed association between compost maturity and suppressiveness was verified in this case. It appears that compost microbial populations might compete and interfere with the saprophytic stage of FOM conidia, between germination and host invasion. In conclusion, it was demonstrated that compost suppressiveness against fusarium wilt of melon can be maintained for at least one year under a wide range of storage conditions, without any loss of suppressive capacity. This fact has positive logistical implications for the use of suppressive composts against FOM.  相似文献   

7.
The objective of this study was to evaluate the effect of sewage sludge on soil suppressiveness to the pathogens Fusarium oxysporum f. sp. lycopersici on tomato, Sclerotium rolfsii on bean, Sclerotinia sclerotiorum on tomato, Rhizoctonia solani on radish, Pythium spp. on cucumber, and Ralstonia solanacearum on tomato. Soil samples were collected from an experimental corn field in which sewage sludge had been incorporated once a year, since 1999. Sludge from two sewage treatment stations in Brazil (Franca and Barueri, SP) were applied at the rates of one (1N), two (2N), four (4N) and eight (8N) times the N recommended doses for the corn crop. Soil suppressiveness was evaluated by methods using indicator host plants, baits and mycelial growth. There was no effect of sewage sludge on soil suppressiveness to Fusarium oxysporum f. sp. lycopersici in tomato plants. For S. rolfsii, reduction of the disease in bean was inversely proportional to the dose of Franca sludge. The incidence of dead plants, caused by S. sclerotiorum, was directly proportional to sludge doses applied. For R. solani and R. solanacearum, there was a linear trend with reduction in plant death in soils treated with increasing amounts of sludge from Franca. There was an increase in the pathogen community of Pythium spp., proportional to the amounts of sewage applied. The effects of sewage sludge varied depending on the pathogen, methodology applied and on the time interval between the sewage sludge incorporation and soil sampling.  相似文献   

8.
The aim of this study was to investigate the potentials and limitations in restoring soil suppressiveness in disturbed soils. Soils from three sites in UK and Switzerland (STC, REC, THE) differing in their level of suppressiveness to soil-borne and air-borne diseases were γ-irradiated and this soil matrix was re-inoculated with 1% (w/w) of either parent native soil or native soil from the other sites (‘soil inoculum’). Suppressiveness to air-borne and soil-borne diseases was quantified by means of the host-pathogen systems Lepidium sativum (cress)-Pythium ultimum, an oomycete causing root rot and seedling damping-off, and Arabidopsis thaliana-Hyaloperonospora parasitica, an oomycete causing downy mildew. Soil microbial biomass, activity and community structure, as determined by phospholipid fatty acid (PLFA) profiles, were measured in native, γ-irradiated, and re-inoculated soils. Both, L. sativum and A. thaliana were highly susceptible to the pathogens if grown on γ-irradiated soils. Re-inoculation completely restored suppressiveness of soils to the foliar pathogen H. parasitica, independently of soil matrix or soil inoculum, whereas suppressiveness to P. ultimum depended on the soil matrix and, to a lesser extent, on the soil inoculum. However, the soil with the highest inherent suppressiveness did not reach the initial level of suppressiveness after re-inoculation. In addition, native microbial populations as defined by microbial biomass, activity and community structure, could not be fully restored in re-inoculated soils. As for suppressiveness to P. ultimum, the soil matrix, rather than the source of soil inoculum was identified as the key factor for re-establishing the microbial community structure. Our data show that soils do not or only slowly fully recover from sterilisation by γ-irradiation, indicating that agricultural soil management practices such as soil fumigation or heat treatments frequently used in vegetable cropping should be avoided.  相似文献   

9.
A cultivation-based approach was used to determine the in vitro antagonistic potential of soil bacteria towards Rhizoctonia solani AG3 and Fusarium oxysporum f. sp. lini (Foln3). Four composite soil samples were collected from four agricultural sites with previous documentation of disease suppression, located in France (FR), the Netherlands (NL), Sweden (SE) and the United Kingdom (UK). Similarly, two sites from Germany (Berlin, G-BR; and Braunschweig, G-BS) without documentation of disease suppression were sampled. Total bacterial counts were determined by plating serial dilutions from the composite soil samples onto R2A, AGS and King's B media. A total of 1,788 isolates (approximately 100 isolates per medium and site) was screened for antifungal activity, and in vitro antagonists (327 isolates) were found amongst the dominant culturable bacteria isolated from all six soils. The overall proportion of antagonists and the number of isolates with inhibitory activity against F. oxysporum were highest in three of the suppressive soils (FR, NL and SE). Characterization of antagonistic bacteria revealed a high phenotypic and genotypic diversity. Siderophore and protease activity were the most prominent phenotypic traits amongst the antagonists. The composition and diversity of antagonists in each soil was site-specific. Nevertheless, none of the antimicrobial traits of bacteria potentially contributing to soil suppressiveness analyzed in this study could be regarded as specific to a given site.  相似文献   

10.
Two fungal plant pathogens, Rhizoctonia solani AG 2-2 and Fusarium oxysporum f.sp. lini, were studied in relation to general responses of soil fungi and bacteria following incorporation of Brassica juncea. Our aim was to understand to what extent the changes in the biological and physicochemical characteristics of the soil could explain the effects on the studied pathogens and diseases, and to determine the temporal nature of the responses. Short-term effects of mustard incorporation (up to 4 months) were investigated in a microcosm experiment, and compared with a treatment where composted plant material was incorporated. In a field experiment, the responses were followed up to 11 months after removal or incorporation of a mustard crop. In general, responses in the variables measured changed more after incorporation of fresh mustard material than after addition of similar amounts of composted plant material (microcosms) or after removal of the mustard crop (field). The soil inoculum potential of R. solani AG 2-2 decreased directly after incorporation of mustard, but increased later to disease levels above those in the untreated soil. Neither of these effects could be explained by changes in the population density of R. solani AG 2-2. Fusarium spp. were less influenced, although an increase in the suppressiveness to Fusarium wilt was observed after mustard incorporation as compared with the treatment where mustard was removed. The microbial responses to mustard incorporation were more pronounced for bacteria than for fungi. After an initial substantial increase, the bacterial density decreased but remained above the levels in the control treatment throughout the experimental periods. The bacterial community structure was modified up to 8 months after mustard incorporation. We conclude that incorporation of fresh mustard influences soil microbial communities, especially the bacteria, and has a potential to control the pathogenic activity of R. solani 2-2 on a short-term perspective. The time dependency in microbial responses is important and should be taken into consideration for the evaluation of the potential of Brassicas to control plant disease on a field scale.  相似文献   

11.
Response of soil microbial communities to compost amendments   总被引：1，自引：0，他引：1  
Soil organic matter is considered as a major component of soil quality because it contributes directly or indirectly to many physical, chemical and biological properties. Thus, soil amendment with composts is an agricultural practice commonly used to improve soil quality and also to manage organic wastes. We evaluated in laboratory scale experiments the response of the soilborne microflora to the newly created soil environments resulting from the addition of three different composts in two different agricultural soils under controlled conditions. At a global level, total microbial densities were determined by classical plate count methods and global microbial activities were assessed by measuring basal respiration and substrate induced respiration (SIR). Soil suppressiveness to Rhizoctonia solani diseases was measured through bioassays performed in greenhouses. At a community level, the modifications of the metabolic and molecular structures of bacterial and fungal communities were assessed. Bacterial community level physiological profiles (CLPP) were determined using Biolog™ GN microtiter plates. Bacterial and fungal community structures were investigated using terminal restriction fragment length polymorphism (T-RFLP) fingerprinting. Data sets were analyzed using analysis of variance and ordination methods of multivariate data. The impact of organic amendments on soil characteristics differed with the nature of the composts and the soil types. French and English spent mushroom composts altered all the biological parameters evaluated in the clayey soil and/or in the sandy silty clay soil, while green waste compost did not modify either bacterial and fungal densities, SIR values nor soil suppressiveness in any of the soils. The changes in bacterial T-RFLP fingerprints caused by compost amendments were not related to the changes in CLPP, suggesting the functional redundancy of soil microorganisms. Assessing the density, the activity and the structure of the soil microflora allowed us not only to detect the impact of compost amendment on soil microorganisms, but also to evaluate its effect at a functional level through the variation of soil disease suppressiveness. Differences in disease suppressiveness were related to differences in chemical composition, in availability of nutrients at short term and in microbial composition due to both incorporation and stimulation of microorganisms by the compost amendments.  相似文献   

12.
Clubroot disease of cruciferous plants caused by the soil-borne pathogen Plasmodiophora brassicae is difficult to control because the pathogen survives for a long time in soil as resting spores. Disease-suppressive and conducive soils were found during the long-term experiment on the impact of organic matter application to arable fields and have been studied to clarify the biotic and abiotic factors involved in the disease suppression. The fact that a large amount of organic matter, 400 t ha−1 yr−1 farmyard manure (FYM) or 100 t ha−1 yr−1 food factory sludge compost (FSC), had been incorporated for more than 15 yr in the suppressive soils and these soils showed higher pH and Ca concentration than the disease conducive soil led us to hypothesize that an increase in soil pH due to the long-term incorporation of Ca-rich organic matter might be the primary cause of the disease suppression. We have designed a highly reproducible bioassay system to examine this hypothesis. The suppressive and conducive soils were mixed with the resting spores of P. brassicae at a rate of 106 spore g−1 soil, and Brassica campestris was grown in a growth chamber for 8 d. The number of root hair infections was assessed on a microscope. It was found that the incorporation of FYM and FSC at 2.5% (w/w) to the conducive soil suppressed the infection and that the finer particles (?5 mm) of FSC inhibited the infection and increased soil pH more effectively. Neutralization of the conducive soil by Ca(OH)2, CaCO3 and KOH suppressed the infection, but the effectiveness of KOH was less than those of Ca(OH)2 and CaCO3. Acidification of the suppressive soils by H2SO4, promoted the infection. The involvement of soil biota in the disease suppression was investigated using the sterilized (γ-ray irradiation) suppressive soils with respect to soil pH. The γ-ray irradiation promoted the infection at pH 5.5, but no infection was observed at pH 7.4 irrespective of the sterilization status. All these observations suggest that soil pH is a major factor in disease suppression by organic matter application and that Ca and soil biota play certain roles in the suppression under the influence of soil pH.  相似文献   

13.
In Switzerland, similar types of rhizosphere pseudomonads producing the biocontrol compound 2,4-diacetylphloroglucinol (Phl) have been found in soils suppressive to Thielaviopsis basicola-mediated black root rot of tobacco as well as in conducive soils. However, most findings were based on the analysis of a limited number of Pseudomonas isolates, obtained from a single experiment and only from T. basicola-inoculated plants. Here, an approach based on denaturing gradient gel electrophoresis (DGGE) of dominant phlD alleles from tobacco rhizosphere provided different phlD migration patterns. Sequencing of phlD-DGGE bands revealed a novel phylogenetic cluster of phlD sequences found in both suppressive and conducive soils in addition to previously-documented phlD alleles. phlD-DGGE bands and alleles differed little from one plant to the next but more extensively from one sampling to the next during the three-year study. Three of the 13 bands and 12 of the 31 alleles were only found in suppressive soil, whereas five bands and 13 alleles were found exclusively in conducive soil. The population structure of phlD+ pseudomonads depended more on the individual soil considered and its suppressiveness status than on inoculation of tobacco with T. basicola. In conclusion, phlD-DGGE revealed additional phlD diversity compared with earlier analyses of individual Pseudomonas isolates, and showed differences in phlD+Pseudomonas population structure in relation to disease suppressiveness.  相似文献   

14.
Fusarium wilts are economically important diseases for which there are no effective chemical control measures. Biological control strategies are becoming efficient alternatives for controlling this disease. The suppressiveness to Fusarium oxysporum f. sp. lycopersici race 1 of grape marc compost and cork compost was evaluated in comparison to peat by using a susceptible cultivar of tomato (Lycopersicon esculentum cv. Marmande). Based on community level physiological profiles, different community structures were evident among the plant growth media evaluated. The peat microbial community, growth medium conducive to wilt, used mostly sugars, while those associated with both composts, the very suppressive grape marc and the moderately suppressive cork, used mostly carboxylic acids, amino acids, amines, phenolic compounds and polymers.  相似文献   

15.
On-farm composting is an efficient, environmentally safe and cost-effective process for recycle vegetable residues into productive cycles. Benefits of these composts could include their ability to mediate soil-borne plant pathogen suppression with a significant impact on eco-friendly crop management. In this work, on-farm composts were assayed for ability to control, both in vitro and in vivo, damping-off causing pathogens Rhizoctonia solani and Sclerotinia minor. Tomato and escarole-derived compost was the most suppressive and, furthermore, together with that derived from artichoke wastes, exhibited multi-suppressive activity. Compost communities, characterized at metabolic and global levels by Biolog system, microbial counting, CO2-release and FDA hydrolysis rate, play a major role in compost-based biological control. The complete biotic inactivation by autoclaving composts, has, in fact, reduced or eliminated their ability in pathogen suppression. Solid state 13C CPMAS-NMR spectroscopy revealed that spectral areas typical for phenolic C, as well as methoxyl C, may be associated to suppressivity mechanism(s). These evidences suggested that the ecological relationships between organic carbon molecular distribution and microbial structure may contribute to discriminate suppressive composts from null and conducive ones. Nutritional microniches in compost may then have profound effects on the community functions, including those linked to the suppressiveness.  相似文献   

16.
Glucosinolate profiles differ among plant species and their isothiocyanate (ITC) derivatives differ in toxicity to nematodes. Successful management of plant-parasitic nematodes by ITCs requires the incorporation of appropriate amounts of glucosinolate-containing biomass. Plant materials, containing glucosinolate-precursors of the ITCs most toxic to nematodes, were selected and applied to soil based upon ITC lethal concentration (LC) values. This provided a reliable and repeatable basis for application rates for suppression of Meloidogyne javanica and Tylenchulus semipenetrans by Brassica hirta and M. javanica by B. juncea. Sufficient biomass of B. hirta to potentially yield 0.03-0.12 μmol ml−1 of glucotropeolin reduced nematode survival compared to similar amounts of broccoli (Brassica oleraceae var. botrytis). At biomass levels providing >0.37 μmol ml−1 of glucotropeolin, mortality of M. javanica was 100% with B. hirta. Biomass of B. juncea potentially yielding 2.82 μmol ml−1 of sinigrin reduced M. javanica survival 65% below that obtained by a similar amount of broccoli. Rates of B. juncea to yield lethal levels of allyl ITC to reduce T. semipenetrans survival underestimated the glucosinolate application rates for this amendment. Application of plant biomass to soil >2.9% w/w reduced M. javanica survival regardless of the glucosinolate concentration of the amendment material. Application of brassicaceous amendments to soil initiates complex and dynamic biological and chemical processes. Despite the inherent complexity, we find that brassicaceous amendments can be applied to achieve consistent and repeatable nematode suppression when based upon the chemistry of the incorporated material.  相似文献   

17.
We studied nine composts derived from wastes and by-products of the olive oil, wine, and Agaricus mushroom agro-industries. They were mixed with peat at 1:3 w w −1 ratios and comparatively evaluated in pot experiments to assess suppressiveness against soil-borne and foliar pathogens of tomato. All compost amendments demonstrated high levels of suppressiveness against Phytophthora nicotianae Breda de Haan in tomato, when they were applied directly after curing (T0) indicating the occurrence of a “general suppression phenomenon” (81–100% decrease in plant disease incidence). They were, however, relatively less effective when applied 9 months after curing (T1, 55–100% disease decrease). Suppressiveness against Fusarium oxysporum f.sp. radicis-lycopersici Jarvis & Shoemaker was relatively lower and varied widely among composts (8–95% and 22–87% decrease in plant disease incidence for T0 and T1, respectively). Three of the composts conferred induced systemic resistance against the foliar pathogen Septoria lycopersici Speg. Biotic properties were determined, including respiration, fluorescein diacetate hydrolysis, and β-glucosidase activity of composts. The comparative evaluation of the nine composts revealed no shared critical biotic or abiotic characteristics indicative of their suppressive effects on the soil-borne and foliar pathogens. The complex origin of compost suppressiveness is discussed and the implementation of individual evaluation of each compost product for a specific use is advocated.  相似文献   

18.
The potential for field soils to cause Aphanomyces root rot of pea (Pisum sativum) was estimated for a large number of samples from commercial pea fields over a period of 5 years, using a greenhouse bioassay. The aim of the research project was to gain a mechanistic understanding of soil suppressiveness to the disease. Regression analysis showed that of the measured soil variables (Ca, Mg, K, P, pH), soil Ca concentrations had the strongest (negative) correlation with disease prevalence, and also a significant negative correlation with disease severity in samples with confirmed presence of the disease. Greenhouse bioassays using a set of non-infested soils inoculated with artificially produced oospore inoculum of the casual organism Aphanomyces euteiches, showed a similar negative correlation between soil Ca content and disease severity. Disease severity was not consistently affected by soil sterilisation, but was lowered by the addition of two different Ca salts. In contrast, addition of sodium bicarbonate to two soils lowered the content of water-soluble Ca in the soils and increased disease severity. Studies of cultures of A. euteiches exposed to varying Ca concentrations in vitro showed that zoospore production was inhibited at submillimolar concentrations, while mycelial growth was stimulated or unaffected. We conclude that free Ca is a major variable controlling the degree of soil suppressiveness against A. euteiches, and that inhibition of zoospore production from oospores is a possible mechanism.  相似文献   

19.
This study was conducted with sugar beet in greenhouse and field at two soil type with different organic matter (containing 2.4 and 15.9% OM, referred as the low- and high-OM soil) conditions in order to investigate seed inoculation of sugar beet, with five N2-fixing and two phosphate solubilizing bacteria in comparison to control and mineral fertilizers (N and P) application. Three bacterial strains dissolved P; all bacterial strains fixed N2 and significantly increased growth of sugar beet. In the greenhouse, inoculations with PGPR increased sugar beet root weight by 2.8-46.7% depending on the species. Leaf, root and sugar yield were increased by the bacterial inoculation by 15.5-20.8, 12.3-16.1, and 9.8-14.7%, respectively, in the experiment of low- and high-OM soil. Plant growth responses were variable and dependent on the inoculants strain, soil organic matter content, growing stage, harvest date and growth parameter evaluated. The effect of PGPR was greater at early growth stages than at the later. Effective Bacillus species, such as OSU-142, RC07 and M-13, Paenibacillus polymyxa RC05, Pseudomonas putida RC06 and Rhodobacter capsulatus RC04 may be used in organic and sustainable agriculture.  相似文献   

20.
Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha−1 to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg−1 in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha−1, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.  相似文献   

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