Soil Fungistasis Research Articles

Manure amendments and fungistasis, and relation with protection of wheat from Fusarium graminearum

Certain soils promote crop health because they are pathogen-suppressive (i.e., fungistatic) or disease-suppressive, but the effect of soil management on these properties is not fully understood. Here, we tested the hypothesis that manure could favor fungistasis by screening 26 manured or non-manured wheat fields from Serbia for their ability to control survival/growth of the fungal plant pathogen Fusarium graminearum Fg1. Quantitative PCR showed that the pathogen grew after inoculation in all 26 autoclaved soils. In absence of autoclaving, the pathogen was stable or grew in 16 soils (37 % manured) but declined in the 10 others (70 % manured). For most soils, there was no significant link between soil chemistry and fungistasis, except with Mionica in western/central Serbia. Mionica soils MI2 and MI3, which had received manure, exhibited higher levels of organic matter and potassium compared with soils MI4 and MI5, which had not received manure and were non-fungistatic. Using Mionica soils, we then tested the hypothesis that fungistatic (manured) soils rather than non-fungistatic (non-manured) soils would protect wheat from F. graminearum disease. Indeed, fungistatic soils were suppressive to wheat damping-off. Non-fungistatic soil MI4 was conducive, as expected, but non-fungistatic soil MI5 turned out to be suppressive. Metabarcoding showed that the structure of prokaryotic and fungal rhizosphere communities depended mostly on field location, with a significant effect of F. graminearum inoculation. In conclusion, our findings show that certain farming practices (here, manure amendments) may promote soil fungistasis towards F. graminearum. However, both fungistatic and non-fungistatic soils can be suppressive to F. graminearum disease in wheat, and their differences in rhizosphere microbiota suggest different phytoprotection mechanisms.

Perennial soil characteristics are the main factor driving in vitro inhibition of the wheat fungal pathogen Fusarium graminearum in a French case study

AbstractSoils are termed ‘suppressive’ when they can limit the emergence and propagation of plant diseases. However, little is known regarding what factors determine suppressiveness and whether they could be improved for a given soil. Agricultural practices, such as tillage systems, influence the properties of the soil, and could be a lever to improve soil suppression of pathogens. In this study, we investigated the impact of soil type and crop management practices on soil suppressiveness towards Fusarium graminearum, a major winter wheat (Triticum aestivum) pathogen. As it is transmitted via crop residues left on soil, F. graminearum is susceptible to soil suppression. Soil suppressiveness has been evaluated in more than a 100 sampled fields in the Limagne plain (Puy‐de‐Dôme, France), to represent a great diversity of soil types (either calcisol, vertisol or fluvisol) and cropping systems (organic, reduced tillage or intensive cropping systems). The physicochemical composition of the sampled soils and crop management practices, identified through farmer surveys, were included in a generalized linear mixed‐effect model to explain soil fungistasis. A fungistasis test was performed by putting a plug of PDA‐agar inoculated with Fusarium in contact with the soil and measuring the area of fungal growth. This test revealed a wide variety of soil fungistatic properties, ranging from conducive soils (22% of soil covered by fungal growth) to very suppressive soils (1% of soil covered). Suppressiveness was related to soil perennial properties (p‐value <.001) rather than practices. Overall, these results show that soil type and composition play a key role in fungistasis, and that soil suppressiveness is a complex, multifactorial process.

Soil Fungistasis against Fusarium Graminearum under Different tillage Systems

The establishment of the harmful pathogen Fusarium graminearum in different agroecosystems may strongly depend on the ability of the soils to suppress its development and survival. This study aimed to evaluate the influence of different soil tillage systems (i.e., conventional tillage, reduced tillage and no-tillage) on soil fungistasis against F. graminearum. Soil samples were collected three times during the plant growing season in 2016 and 2017 from a long-term, 20-year soil tillage experiment. The F. graminearum in the soil samples was quantified by real-time qPCR. The soil fungistasis was evaluated by the reduction in the radial growth of F. graminearum in an in vitro assay. The antagonistic activity of the soil bacteria was tested using the dual culture method. The F. graminearum DNA contents in the soils were negatively correlated with soil fungistasis (r = -0.649 *). F. graminearum growth on the unfumigated soil was reduced by 70-87% compared to the chloroform fumigated soil. After the plant vegetation renewal, the soil fungistasis intensity was higher in the conventionally tilled fields than in the no-tillage. However, no significant differences were obtained among the tillage treatments at the mid-plant growth stage and after harvesting. 23 out of 104 bacteria isolated from the soil had a moderate effect, and only 1 had a strong inhibitory effect on the growth of F. graminearum. This bacterium was assigned 100% similarity to the Bacillus amyloliquefaciens Hy7 strain (gene bank no: JN382250) according to the sequence of the 16S ribosome subunit coding gene. The results of our study suggest that the presence of F. graminearum in soil is suppressed by soil fungistasis; however, the role of tillage is influenced by other factors, such as soil biological activity, type and quantity of plant residues and environmental conditions.

Winter wheat grain production using organic farming technology

The influence of microbiological preparations on the soil fertility of leached chernozem and the productivity of winter wheat was studied. Treatment of seeds with preparations of various preparative forms (CE and powder) increases microbiological activity and balances the nutrient regime of the soil. When seedlings appeared, the number of ammonifying microorganisms in the studied variants was 126-185 % higher than the control variant. The introduction of drugs in the indicated dosage at the rate of 300 l/ha of the working solution further contributed to the growth of this group of microorganisms, they were 4-9 times higher than the number of bacteria in the control variant. Microbiological preparations increased soil fungistasis. The number of soil micromycetes decreased by 46-62 % during the entire growing season of wheat. The development of fungi of the genus Fusarium was also inhibited. Their number was an order of magnitude lower in the studied variants, compared with the control. Microbiological preparations, converting phosphorus and potassium compounds into an easily accessible form, contributed to an increase in the content of P2O5 in winter wheat crops, in the studied variants by 1.6-1.9 times, and K2O 1.3-1.6 times higher than the control variant. The yield of winter wheat on the variants of using biological preparations in 2021 exceeded the control variant by 6.5 and 12.4 %, and in 2022 by 7.3-10.2 %. The yield of winter wheat under the traditional technology of its cultivation practically did not exceed the options for using the studied preparations.

Dormancy and germination of microsclerotia of Verticillium longisporum are regulated by soil bacteria and soil moisture levels but not by nutrients

The soil-borne pathogen Verticillium longisporum infects roots of its host plant, oilseed rape, and systemically colonizes stems where it finally forms microsclerotia at crop maturity. Once returned to the soil after harvest, microsclerotia undergo a stage of dormancy, in which they may survive for several years. Since there is neither efficient chemical control nor effective resistance in oilseed rape cultivars to control the disease, alternative control strategies may consist in regulating the germination and dormancy of microsclerotia in the soil. Therefore, a series of experiments were conducted to explore the effects of nutrients, soil moisture, and the soil microbiome on germination of dormant microsclerotia. Experiments with microsclerotia exposed in vitro to different nutrients indicated that under sterile conditions the stimulating effect of nutrients on microsclerotia germination was not enhanced as compared to water. Moreover, further assays revealed a strong inhibitory effect of unsterile soil on microsclerotia germination. Accordingly, oilseed rape plants inoculated with microsclerotia of V. longisporum showed severe infection with V. longisporum when grown in autoclaved soil, in contrast to plants grown in unsterile soil. These experiments indicate a crucial role of soil fungistasis and thus the soil microbiome on microsclerotia germination. Further bioassays demonstrated that viable soil bacteria obtained from the rhizosphere of oilseed rape plants and bulk field soil effectively inhibited microsclerotia germination, whereas dead bacteria and bacterial culture filtrates hardly suppressed germination. A putative inhibitory role of volatile organic compounds (VOCs) produced by soil bacteria was confirmed in two-compartment Petri dishes, where microsclerotia germination and colony growth were significantly inhibited. Bacterial VOCs were collected and analyzed by GC–MS. In total, 45 VOCs were identified, among which two acid and two alcohol compounds were emitted by all tested bacteria. A bioassay, conducted with corresponding pure chemicals in two-compartment Petri dishes, indicated that all acidic volatile compounds, including 3-methylbutanoic acid, 2-methylbutanoic acid, hexanoic acid, and 2-methylpropionic acid, induced strong inhibitory effects on microsclerotia. We conclude that bacterial acidic volatiles play a key role in the fungistatic effect on microsclerotia of V. longisporum in the soil and could thus be targeted for development of novel strategies to control this pathogen by artificially regulating dormancy of microsclerotia in soil.

Fungistatic Mechanism of Ammonia against Nematode-Trapping Fungus Arthrobotrys oligospora, and Strategy for This Fungus To Survive Ammonia.

ABSTRACTSoil fungistasis is a phenomenon in which the germination and growth of fungal propagules is widely inhibited in soils. Although fungistatic compounds are known to play important roles in the formation of soil fungistasis, how such compounds act on soil fungi is little studied. In this study, it was found that ammonia (NH3) induced global protein misfolding marked by increased ubiquitination levels of proteins (ubiquitylome data and Western blot verification). The misfolded proteins should trigger the endoplasmic reticulum (ER) stress, which was indicated by electron microscope image and proteome data. Results from the mutants of BiP and proteasome subunit alpha 7 suggested that ER stress played a mechanistic role in inhibiting conidial germination. Results from proteome data indicated that, to survive ammonia fungistasis, conidia first activated the unfolded protein response (UPR) to decrease ER stress and restore ER protein homeostasis, and the function of UPR in surviving ammonia was confirmed by using mutant strains. Second, ammonia toxicity could be reduced by upregulating carbon metabolism-related proteins, which benefited ammonia fixation. The results that metabolites (especially glutamate) could relieve the ammonia fungistasis confirmed this indirectly. Finally, results from gene knockout mutants also suggested that the fungistatic mechanism of ammonia is common for soil fungistasis. This study increased our knowledge regarding the mechanism of soil fungistasis and provided potential new strategies for manipulating soil fungistasis.IMPORTANCE Soil fungistasis is a phenomenon in which the germination and growth of fungal propagules is widely inhibited in soil. Although fungistatic compounds are known to play important roles in the formation of soil fungistasis, how such compounds act on soil fungi remains little studied. This study revealed an endoplasmic reticulum stress-related fungistatic mechanism with which ammonia acts on Arthrobotrys oligospora and a survival strategy of conidia under ammonia inhibition. Our study provides the first mechanistic explanation of how ammonia impacts fungal spore germination, and the mechanism may be common for soil fungistasis. This study increases our knowledge regarding the mechanism of soil fungistasis in fungal spores and provides potential new strategies for manipulating soil fungistasis.

Methylglyoxal Has Different Impacts on the Fungistatic Roles of Ammonia and Benzaldehyde, and Lactoylglutathione Lyase Is Necessary for the Resistance of Arthrobotrys oligospora to Soil Fungistasis.

Biocontrol of root-knot nematode has attracted increasing attention over the past two decades. The inconsistent field performance of biocontrol agents, which is caused by soil fungistasis, often restricts their commercial application. There is still a lack of research on the genes involved in biocontrol fungi response to soil fungistasis, which is important for optimizing practical applications of biocontrol fungi. In this study, the lactoylglutathione lyase-encoding AOL_s00004g335 in the nematophagous fungi Arthrobotrys oligospora was knocked out, and three mutant strains were obtained. The hyphal growth of mutants on the three media was almost the same as that of the wild-type strain, but mutants had slightly higher resistance to NaCl, SDS, and H2O2. Methylglyoxal (MG) significantly increased the resistance of A. oligospora to ammonia, but decreased the resistance to benzaldehyde. Furthermore, the resistance of the mutants to soil fungistasis was largely weakened and MG could not increase the resistance of A. oligospora to soil fungistasis. Our results revealed that MG has different effects on the fungistatic roles of ammonia and benzaldehyde and that lactoylglutathione lyase is very important for A. oligospora to resist soil fungistasis.

Tillage System and Crop Sequence Affect Soil Disease Suppressiveness and Carbon Status in Boreal Climate.

The soil-borne plant pathogens cause serious yield losses and are difficult to control. In suppressive soils, disease incidence remains low regardless of the presence of the pathogen, the host plant, and favorable environmental conditions. The potential to improve natural soil disease suppressiveness through agricultural management practices would enable sustainable and resilient crop production systems. Our aim was to study the impact of autumn tillage methods and crop sequence on the soil carbon status, fungistasis and yield in boreal climate. The disease suppression was improved by the long-term reduced and no tillage management practices with and without crop rotation. Compared to the conventional plowing, the non-inversion tillage systems were shown to change the vertical distribution of soil carbon fractions and the amount of microbial biomass by concentrating them on the soil surface. Crop sequence and the choice of tillage method had a combined effect on soil organic carbon (SOC) sequestration. The improved general disease suppression had a positive correlation with the labile carbon status and microbial biomass. From the most common Fusarium species, the predominantly saprophytic F. avenaceum was more abundant under non-inversion practice, whereas the opposite was true for the pathogenic ones. Our findings furthermore demonstrated the correlation of the soil fungistasis laboratory assay results and the prevalence of the pathogenic test fungus Fusarium culmorum on the crop cereals in the field. Our results indicate that optimized management strategies have potential to improve microbial related soil fungistasis in boreal climate.

Comparative Transcriptomics Reveals Features and Possible Mechanisms of Glucose-Mediated Soil Fungistasis Relief in Arthrobotrys oligospora.

Soil-borne pest diseases result in large annual agricultural losses globally. Fungal bio-control agents are an alternative means of controlling pest diseases; however, soil fungistasis limits the effect of fungal agents. Nutrients can relieve soil fungistasis, but the mechanisms behind this process remain poorly understood. In this study, we determined and quantified the transcriptomes of Arthrobotrys oligospora, a nematode-trapping fungus, derived from samples of fresh conidia, germinated conidia, soil fungistatic conidia, and glucose-relieved conidia. The transcriptomes of fungistatic and glucose-relieved conidia were significantly different from those of the other two conidia samples. KEGG pathway analyses showed that those genes upregulated in fungistatic and glucose-relieved conidia were mainly involved in translation and substance metabolism, and the downregulated genes were mainly involved in MAPK pathway, autophagy, mitophagy, and endocytosis. As being different from the transcriptome of fungistatic conidia, upregulated genes in the transcriptome of glucose-relieved conidia are also related to replication and repair, spliceosome, oxidative phosphorylation, autophagy, and degradation pathway (lysosome, proteasome, and RNA degradation). And the upregulated genes resulted from comparison of glucose-relieved conidia and fungistatic conidia were enriched in metabolic pathways, cycle, DNA replication, and repair. The differentially splicing events in the transcriptome of glucose-relieved conidia are far more than that of other two transcriptomes, and genes regulated by differentially splicing were analyzed through KEGG pathway analysis. Furthermore, autophagy genes were proved to play important role in resisting soil fungistasis and glucose-mediated soil fungistasis relief. These data indicate that, in addition to being a carbon and energy source for conidia germination, glucose may also help to relieve soil fungistasis by activating many cellular processes, including autophagy, DNA replication and repair, RNA alternative splicing, and degradation pathways.

Volatile-mediated antagonism of soil bacterial communities against fungi.

SummaryCompetition is a major type of interaction between fungi and bacteria in soil and is also an important factor in suppression of plant diseases caused by soil‐borne fungal pathogens. There is increasing attention for the possible role of volatiles in competitive interactions between bacteria and fungi. However, knowledge on the actual role of bacterial volatiles in interactions with fungi within soil microbial communities is lacking. Here, we examined colonization of sterile agricultural soils by fungi and bacteria from non‐sterile soil inoculums during exposure to volatiles emitted by soil‐derived bacterial communities. We found that colonization of soil by fungi was negatively affected by exposure to volatiles emitted by bacterial communities whereas that of bacteria was barely changed. Furthermore, there were strong effects of bacterial community volatiles on the assembly of fungal soil colonizers. Identification of volatile composition produced by bacterial communities revealed several compounds with known fungistatic activity. Our results are the first to reveal a collective volatile‐mediated antagonism of soil bacteria against fungi. Given the better exploration abilities of filamentous fungi in unsaturated soils, this may be an important strategy for bacteria to defend occupied nutrient patches against invading fungi. Another implication of our research is that bacterial volatiles in soil atmospheres can have a major contribution to soil fungistasis.

Phytomonitoring of woody plants in the urban agglomeration

Phytomonitoring including mycological studies with information about plant pathogens, etc., is required to develop strategic directions for maintaining green spaces in urban agglomeration. Mycological analysis of the aerial part and roots of urban tree plants can be used to determine the composition and structures of microbial-plant associations in visually healthy and affected plants. The relevance of these works is due to rapid development of diseases and pests and their active distribution in close proximity to city residents. In coniferous and deciduous plants with symptomatic lesions (Picea abies (L.) H. Karst., Pinus spp., Quercus robur L., Tilia spp.), the species diversity of micromycetes in the phylloplane and rhizosphere decreased by 21–38% compared to visually healthy plants. It was suggested using the following micromycetes as marker organisms for assessing the soil fungistasis of artificial bicenoses and the state of coniferous trees: Dicoccum sp., Fusarium moniliforme J. Sheld., Fusarium culmorum. Perennial urban plants require improvement of the above-ground part using foliar fertilizers and phytostimulants, bioprotection tools, humates, mycorrhizal preparations, destructors of organic compounds of roots and adjacent lawns. The prospects of phytomonitoring of old-growing trees were emphasized. Reconstruction and enhancement of their resistance to aggressive environments require complex works.

Conservation agriculture: new crop production technologies

Among the arguments in favor of new crop production technologies are the need for improvement of regional ecology and biodiversity, and high-quality biological products. Methods for reducing crop losses caused by air and soil droughts in the central and southern regions of Russia were analyzed. Field observations (2010-2016) were carried out using a crop rotation scheme of experimental fields with a wide range of crop varieties: wheat, barley, corn, sunflower, peas, chickpeas, alfalfa, and flax. The purpose of the article is to assess regional characteristics of effective soil fertility using different resource-saving technologies. Biological productivity (regional, local) was used as an integral indicator of effectiveness of agricultural technologies and crop yields. High effective fertility was observed when using a zero agrotechnology in Volgograd region and minimum tillage method in Stavropol region. The need for the control of soil fungistasis as a basis of biological activity of the soil and long-term improvement of effective fertility of the arable land was emphasized.

Sandy soils amended with bentonite induced changes in soil microbiota and fungistasis in maize fields

The addition of bentonite, used as soil conditioner, can promote sandy soil macro-aggregate formation, moisture content retention and increase soil nutrient concentrations. However, there is limited knowledge about how bentonite influences soil microbial communities and interconnections among community members associated with crops, such as maize in continuous production on sandy soils. Metabarcoding analysis of the fungal internal transcribed spacer 1 (ITS1) region and the bacterial 16S rRNA gene V4 region revealed that the fungal communities in sandy maize fields (dominated by Guehomyces, Alternaria and Mortierella) were more diverse and abundant in soils amended with bentonite than those without bentonite amendment. By contrast, the bacterial communities (dominated by Proteobacteria and Actinobacteria) had similar alpha-diversity under both conditions but many functional guilds, including those affiliated with fermentation and N-cycling, differed significantly in community compositional structure between soils with and without bentonite amendment. The increase in soil nutrient concentrations due to the addition of bentonite was a key factor associated with changes in the bacterial communities. However, the fungal communities were more strongly influenced by the capacity of bentonite to increase soil moisture retention and enhance macro-aggregate development. Molecular ecological network analysis revealed more competitive (62.1% of total significant associations) than cooperative (37.9%) associations among microbial community members across all soils studied. The observation that fungal phytopathogens recovered from bentonite-amended soils had more negative correlations (75.6%) with naturally occurring beneficial bacteria and/or fungi than those in non-bentonite soils (65.2%), perhaps suggests, although speculation, that the addition of bentonite promoted soil fungistasis. In summary, our study showed that the addition of bentonite increased maize productivity and reshaped the microbial functional guilds in sandy soils, a consequence of improved soil structure as well as water and nutrient retention; however, the amendment’s long-term impact on soil suppressiveness to fungal phytopathogens is worth further investigation.

Co-occurrence analysis reveal that biotic and abiotic factors influence soil fungistasis against Fusarium graminearum.

The current study determined the levels of soil fungistasis against a soil-borne pathogen inoculum, Fusarium graminearum (Fg, a major causal agent of Fusarium Head Blight (FHB)), in 31 wheat fields by quantifying Fg growth after a 15-day incubation period using qPCR in autoclaved versus non-autoclaved soils. The results were used to define the six most Fg-resistant and the six most Fg-conducive soils. By using a metabarcoding approach, the diversity of the bacterial communities was significantly higher in Fg-resistant soils than in Fg-conducive soils. Microbial taxa potentially contributing to Fg-fungistasis of soil were selected if they were significantly more prevalent and/or abundant in Fg-resistant soils than in Fg-conducive soils. Some of these candidate indicators, e.g. Pseudomonas spp. and Bacillus spp., have been reported previously as effective biocontrol agents against plant pathogens. Correlation-based network analysis further showed that the members of the bacterial communities in Fg-resistant soils were more connected than in Fg-conducive soils. Moreover, network modules was found significantly correlated with certain edaphic abiotics factors (such as the soil manganese and nitrogen content) and Fg-fungistasis. Such observations may suggest and emphasize, although conceptual, the importance of synergistic rather than individual effects of network members, and the nutrient use efficiency in contributing to Fg-resistance of soils in wheat fields in France.

Proteomic changes in Arthrobotrys oligospora conidia in response to benzaldehyde-induced fungistatic stress

Soil fungistasis limits the effect of fungal agents designed to control plant-parasitic nematodes. Benzaldehyde is a fungistatic factor produced by soil microorganisms that can suppress conidial germination, but the molecular mechanism of this suppression is unknown. In this study, three conidial proteomes of Arthrobotrys oligospora ATCC24927, a nematode-trapping fungus, were obtained, quantified, and compared. Under benzaldehyde fungistatic stress, conidial protein expression profile changed significantly. Screening with a twofold selection criterion revealed 164 up-regulated and 110 down-regulated proteins. 17 proteins related to protein translation were down-regulated and gene transcription analysis suggested that the repression of proteins translation might be one mechanism by which benzaldehyde inhibites conidial germination. Benzaldehyde also resulted in the down-regulation of respiratory chain proteins and mitochondrial processes, as well as the repression of conidial DNA synthesis. In addition, the conidia up-regulated several proteins that enable it to resist benzaldehyde-induced fungistatis, and this was confirmed by a functional assessment of two knockout mutants. This study reveals putative mechanisms by which benzaldehyde causes fungistasis as well as the proteomic response of conidia to benzaldehyde. SignificanceSoil fungistasis limits the effect of fungal agents designed to control plant-parasitic nematodes. Benzaldehyde is one of fungistatic factors produced by soil microorganisms that can suppress conidial germination. In this study, we found that conidial protein expression profile changed significantly under benzaldehyde fungistatic stress. This research revealed new mechanistic data that describe how benzaldehyde is responsible for fungiststis by inhibiting conidial germination. Moreover, we also found that conidia can resist benzaldehyde by up-regulating proteins such as benzaldehyde dehydrogenase and heat shock proteins. This study also showed that proteomics methods play important roles in addressing soil fungistatic mechanisms.

土壌静菌作用 : 糸状菌の生活に及ぼす生態的意義(土の微生物世界)

土壌静菌作用 : 糸状菌の生活に及ぼす生態的意義(土の微生物世界)

The antimicrobial volatile power of the rhizospheric isolate Pseudomonas donghuensis P482.

Soil and rhizosphere bacteria produce an array of secondary metabolites including a wide range of volatile organic compounds (VOCs). These compounds play an important role in the long-distance interactions and communication between (micro)organisms. Furthermore, bacterial VOCs are involved in plant pathogens inhibition and induction of soil fungistasis and suppressivenes. In the present study, we analysed the volatile blend emitted by the rhizospheric isolate Pseudomonas donghuensis P482 and evaluated the volatile effect on the plant pathogenic fungi and bacteria as well as one oomycete. Moreover, we investigated the role of the GacS/GacA system on VOCs production in P. donghuensis P482. The results obtained demonstrated that VOCs emitted by P. donghuensis P482 have strong antifungal and antioomycete, but not antibacterial activity. The production of certain volatiles such as dimethyl sulfide, S-methyl thioacetate, methyl thiocyanate, dimethyl trisulfide, 1-undecan and HCN is depended on the GacS/GacA two-component regulatory system. Apparently, these compounds play an important role in the pathogens suppression as the gacA mutant entirely lost the ability to inhibit via volatiles the growth of tested plant pathogens.

Frequent Applications of Organic Matter to Agricultural Soil Increase Fungistasis

Soil–borne plant pathogens are among the most important limiting factors for the productivity of agro–ecosystems. Fungistasis is the natural capability of soils to inhibit the germination and growth of soil–borne fungi in the presence of optimal abiotic conditions. The objective of this study was to assess the effects of different soil managements, in terms of soil amendment types and frequency of application, on fungistasis. For this purpose, a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i. e., glucose, alfalfa straw and wheat straw). Thereafter, the fungistasis response was assessed on four fungi (Aspergillus niger, Botrytis cinerea, Pyrenochaeta lycopersici and Trichoderma harzianum). Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method. Results showed that irrespective of the fungal species and amendment types, frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration. The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities. This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity.

Screening of Trichoderma isolates for their potential of biosorption of nickel and cadmium.

Fourteen Trichoderma isolates were evaluated for their tolerance to two heavy metals, nickel and cadmium. Three isolates, MT-4, UBT-18, and IBT-I, showed high levels of nickel tolerance, whereas MT-4, UBT-18, and IBT-II showed better tolerance of cadmium than the other isolates. Under nickel stress, biomass production increased up to a Ni concentration of 60 ppm in all strains but then decreased as the concentrations of nickel were further increased. Among the nickel-tolerant isolates, UBT-18 produced significantly higher biomass upon exposure to nickel (up to 150 ppm); however, the minimum concentration of nickel required to inhibit 50% of growth (MIC50) was highest in IBT-I. Among the cadmium-tolerant isolates, IBT-II showed both maximum biomass production and a maximum MIC50 value in cadmium stress. As the biomass of the Trichoderma isolates increased, a higher percentage of nickel removal was observed up to a concentration of 40 ppm, followed by an increase in residual nickel and a decrease in biomass production at higher nickel concentrations in the medium. The increase in cadmium concentrations resulted in a decrease in biomass production and positively correlated with an increase in residual cadmium in the culture broth. Nickel and cadmium stress also influenced the sensitivity of the Trichoderma isolates to soil fungistasis. Isolates IBT-I and UBT-18 were most tolerant to fungistasis under nickel and cadmium stress, respectively.

Response of soil fungi and biological processes to crop residues in no-tillage system

ABSTRACT Soil management and crop rotation can directly affect the soil microbial community. This study aimed at determining soil quality indicators and soilborne fungi in a no-tillage system. A randomized blocks design, in a 3 × 2 factorial arrangement, was used. Three cover crops (palisade grass, millet and common bean) provided straw and root residues to the following crops of corn and soybean. The common bean-soybean sequence provided little soil covering and higher metabolic quotient and soil basal respiration and total enzymatic activity, as well as a general increase of soilborne fungi. The principal component analysis revealed that 76.61 % of the variance can be explained by the three first components, with cover crops, soil basal respiration and metabolic quotient regarded as the main qualitative and quantitative sources of variance in the first component. Carbon from the microbial biomass was the soil quality indicator best correlated to crop yield and negatively correlated to Fusarium solani density. The Rhizoctonia solani population was correlated with higher metabolic quotient and soil total enzymatic activity and basal respiration. The palisade grass crop favored soil fungistasis and enhancement of antagonist Trichoderma spp. populations. The multivariate approach demonstrated the association of soil fungi with soil quality indicators, as well as a higher influence of cover crops on the variance observed, in comparison to cash crops.