Combined use of biocontrol agents and zeolite as a management strategy against <Emphasis Type="Italic">Fusarium</Emphasis> and <Emphasis Type="Italic">Verticillium</Emphasis> wilt

Vascular wilt pathogens, like Fusarium oxysporum and Verticillium dahliae, cause heavy economic loses to a range of crops. The lack of chemical control intensifies the problem. In the present study, the initial in vitro activity of 134 bacterial isolates, originating from various stages of the composting process of cotton residues, against F. oxysporum f. sp. melonis (FOM) and V. dahliae was evaluated. The most efficient strains, named SP10 and C20 M, belong to Bacillus sp. Both strains significantly reduced Fusarium and Vertilicillium wilt in melon and aubergine respectively. Furthermore, zeolite was tested alone or in combination with SP10 against V. dahliae and FOM. It was shown that the combination of zeolite and SP10 in the transplant soil plug was the most disease suppressive treatment. Interestingly the single application of zeolite was also plant-protective. The positive effect of zeolite on plant health could be linked with the recorded up-regulation of plant defense genes.     

Evaluation of Compost Amendments for Control of Vascular Wilt Diseases

Vascular wilt fungal pathogens cause heavy economic losses to a wide range of crops; amongst them are Fusarium oxysporum f. sp. melonis (FOM) and Verticillium dahliae Kleb. Several strategies for controlling these pathogens have been introduced, such as soil solarization, resistant rootstocks and biological control. In this study, the suppressive ability of seven different compost amendments and the plant growth-promoting rhizobacterium Paenibacillus alvei K165 (with proven activity against V. dahliae ) were tested against FOM in melon and V. dahliae in eggplant. It was shown that K165 had a suppressive effect against the pathogens in all experiments. On the contrary, the composts exhibited a narrow spectrum of effectiveness against the pathogens. Two composts were effective against V. dahliae and one against FOM. Moreover, we investigated the potential of the various compost samples and K165 to induce resistance in an Arabidopsis thaliana – V. dahliae or FOM model system. It was demonstrated that three composts and K165 were effective against V. dahliae ; whereas, one compost and K165 were effective against FOM. In a naturally V.dahliae infested field, the ability of K165 to enhance the suppressive effect of one of the compost amendments, was evaluated. It was demonstrated that fortification of the compost with strain K165 significantly reduced disease severity, whereas the single application of the compost was not sufficient to significantly protect the plants.     

Evaluation of a liquid formulation of Pseudomonas fluorescens against Fusarium oxysporum f. sp. cubense and Helicotylenchus multicinctus in banana plantation

Plant growth promoting rhizobacteria (PGPR) are eco-friendly alternatives to chemical fungicides to manage plant diseases. We evaluated the efficacy of a Pseudomonas fluorescens formulation against Fusarium oxysporum f. sp. cubense and Helicotylenchus multicinctus at multiple banana plantations. Three field trials were conducted to assess the wilt incidence and the populations of nematode and bacteria in the soil treated with a liquid formulation of P. fluorescens at 2.0, 3.0 and 4.0 l ha^?1 using drip irrigation system at 60, 120, 180 and 240 days after planting. The results showed that the treatment at 4.0 l ha^?1 reduced the wilt incidence by 60 %. It also reduced the overall population of H. multicinctus by 41.3–89.0 % in the treated fields. The presence of P. fluorescens in the treated soil was 5.6 × 10⁶ cfu g^?1 of soil at the time of harvest. The treatment of biocontrol agent P. fluorescens also resulted in an overall yield increase in banana production by 36.6–46.5 % compared to the control.     

Suppression of wheat Fusarium head blight by novel amphiphilic aminoglycoside fungicide K20

K20 is a novel amphiphilic aminoglycoside capable of inhibiting many fungal species. K20's capabilities to inhibit Fusarium graminearum the causal agent wheat Fusarium head blight (FHB) and to this disease were examined. K20 inhibited the growth of F. graminearum (minimum inhibitory concentrations, 7.8–15.6 mg L^?1) and exhibited synergistic activity when combined with triazole and strobilurin fungicides. Application of K20 up to 720 mg L^?1 to wheat heads in the greenhouse showed no phytotoxic effects. Spraying wheat heads in the greenhouse with K20 alone at 360 mg L^?1 lowered FHB severity below controls while combining K20 with half–label rates of Headline (pyraclostrobin) improved its disease control efficacy. In field trials, spraying K20 at 180 mg L^?1 and 360 mg L^?1 combined with half-label rates of Headline, Proline 480 SC (prothioconazole), Prosaro 421 SC (prothioconazole + tebuconazole), and Caramba (metconazole) reduced FHB indices synergistically. In addition, the K20 plus Proline 480 SC combination reduced levels of the mycotoxin deoxinivalenol by 75 % compared to the control. These data suggest that K20 may be useful as a fungicide against plant diseases such as FHB particularly when combined with commercial fungicides applied at below recommended rates.     

Strain-specific and recessive QTLs involved in the control of partial resistance to Fusarium oxysporum f. sp. melonis race 1.2 in a recombinant inbred line population of melon

Fusarium oxysporum f. sp. melonis (FOM) causes serious economic losses in melon (Cucumis melo L.). Two dominant resistance genes have been identified, Fom-1 and Fom-2, which provide resistance to races 0 and 2 and races 0 and 1, respectively, however FOM race 1.2 overcomes these resistance genes. A partial resistance to FOM race 1.2 that has been found in some Far East accessions is under polygenic control. A genetic map of melon was constructed to tag FOM race 1.2 resistance with DNA markers on a recombinant inbred line population derived from a cross between resistant (Isabelle) and susceptible (cv. Védrantais) lines. Artificial root inoculations on plantlets of this population using two strains, one that causes wilting (FOM 1.2w) and one that causes yellowing (FOM 1.2y), resulted in phenotypic and genotypic data that enabled the identification of nine quantitative trait loci (QTLs). These QTLs were detected on five linkage groups by composite interval mapping and explained between 41.9% and 66.4% of the total variation. Four digenic epistatic interactions involving seven loci were detected and increased the total phenotypic variation that was explained. Co-localizations between QTLs and resistance gene homologs or resistance genes, such as Fom-2 and Vat, were observed. A strain-specific QTL was detected, and some QTLs appeared to be recessive.     

Construction of a genome-anchored,high-density genetic map for melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) and identification of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">melonis</Emphasis> race 1 resistance QTL

Key message

Four QTLs and an epistatic interaction were associated with disease severity in response to inoculation with Fusarium oxysporum f. sp. melonis race 1 in a recombinant inbred line population of melon.

Abstract

The USDA Cucumis melo inbred line, MR-1, harbors a wealth of alleles associated with resistance to several major diseases of melon, including powdery mildew, downy mildew, Alternaria leaf blight, and Fusarium wilt. MR-1 was crossed to an Israeli cultivar, Ananas Yok’neam, which is susceptible to all of these diseases, to generate a recombinant inbred line (RIL) population of 172 lines. In this study, the RIL population was genotyped to construct an ultra-dense genetic linkage map with 5663 binned SNPs anchored to the C. melo genome and exhibits the overall high quality of the assembly. The utility of the densely genotyped population was demonstrated through QTL mapping of a well-studied trait, resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Fom) race 1. A major QTL co-located with the previously validated resistance gene Fom-2. In addition, three minor QTLs and an epistatic interaction contributing to Fom race 1 resistance were identified. The MR-1 × AY RIL population provides a valuable resource for future QTL mapping studies and marker-assisted selection of disease resistance in melon.

     

Streptomyces sp. S160: a potential antagonist against chickpea charcoal root rot caused by Macrophomina phaseolina (Tassi) Goid

Biological control of charcoal root rot disease caused by Macrophomina phaseolina in chickpea was studied by using Streptomyces sp. S160. This biocontrol agent (BCA) inhibited the mycelial growth of M. phaseolina by 50 % in vitro and significantly reduced charcoal rot incidence in the greenhouse by 33.3 %. The greenhouse experiment revealed that seed treatment along with soil application supported the highest germination (88.6 %), vigor index (7326.91) and reduced root rot incidence (12.5 %) in comparison to seed treatment and soil application alone. BCA enhanced the growth and helped in inducing resistance against charcoal rot disease of chickpea caused by M. phaseolina by increasing activity of defense-related enzymes in chickpea plants, leading to the synthesis of defense chemicals in plants. BCA (Streptomyces sp. S160) was also characterized and identified by using polyphasic approaches including 16S rDNA sequencing.     

Effect of Paenibacillus alvei, strain K165, on the germination of Verticillium dahliae microsclerotia in planta

Verticillium wilt is a devastating disease of a wide range of herbaceous and woody plant hosts, incited by the soilborne fungus Verticillium dahliae. In the present study, the effect of the potential biocontrol isolate Paenibacillus alvei, strain K165, on the germination of V. dahliae microsclerotia (msc) was investigated. Strain K165 was isolated from tomato root tips and its activity against V. dahliae has been shown in glasshouse and field experiments. In the present study, the application of K165 resulted in the reduction of msc germination of V. dahliae, in the root tips and the zone of elongation, of eggplants by 50% compared to the control treatment; whereas 10 and 12 cm away from root tips and in soil without plants the percentage of msc germination was reduced by 26% and 40%, respectively. However, K165 did not significantly affect the number and length of hyphae per germinated msc. In a split-root system, K165 triggered induced systemic resistance in eggplants against V. dahliae by reducing disease severity and msc germination by 27% and 20%, respectively. In addition, K165 colonised the rhizosphere of eggplants and soil in a population density of 5 and 3 log₁₀ cfu g⁻¹, 7 dpi, respectively. This is the first report of evaluating the direct/indirect effect of a rhizospheric bacterium on msc germination in the rhizosphere of eggplants, indicating that strain K165 reduces msc germination.     

Genetic Diversity and Pathogenicity of Fusarium oxysporum f.sp. melonis Races from Different Areas of Italy

Fusarium wilt caused by Fusarium oxysporum f.sp. melonis (FOM) is a devastating disease of melon worldwide. Pathogenicity tests performed with F. oxysporum isolates obtained from Italian melon‐growing areas allowed to identify thirty‐four FOM isolates and the presence of all four races. The aims of this work were to examine genetic relatedness among FOM isolates by race determination and to perform phylogenetic analyses of identified FOM races including also other formae speciales of F. oxysporum of cucurbits. Results showed that FOM race 1,2 was the most numerous with a total of eighteen isolates, while six and nine isolates were identified as race 0 and 1, respectively, and just one isolate was assigned to race 2. Phylogenetic analysis was performed by random amplified polymorphic DNA (RAPD) profiling and by translation elongation factor‐1α (TEF‐1α) sequencing. The analysis of RAPD profiles separated FOM races into two distinct clades. Clade 1, which included races 0, 1 and 1,2, was further divided into ‘subclade a’ which grouped almost all race 1,2 isolates, and into ‘subclade b’ which included race 0 and 1 isolates. Clade 2 comprised only race 2 isolates. The phylogenetic analysis based on TEF‐1α separated FOM from the other formae speciales of F. oxysporum. Also with TEF‐1α analysis, FOM races 0, 1 and 1,2 isolates grouped in one single clade clearly separated from FOM race 2 isolates which grouped closer to F. oxysporum f.sp. cucumerinum. RAPD technique was more effective than TEF‐1α in differentiating FOM race 1,2 isolates from those belonging to the closely related races 0 and 1. Both phylogenetic analyses supported the close relationship between the three different FOM races which might imply the derivation from one another and the different origin of FOM race 2.     

Efficacy of bacterial seed treatments for the control of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> in maize

Maize colonization by the phytopathogenic fungi Fusarium verticillioides leads to economical and food quality losses and also implicates potential health risks. In order to control this fungal species different strategies are being considered. In the present work we investigated the in situ effects of the use of two in vitro proven bacterial biological control agents against Fusarium verticillioides, using maize seedlings grown in greenhouse conditions. The treatment of maize seeds with Fusarium verticillioides 10⁷ spores ml^?1 negatively affected the length of the stem and the weight of the root systems of resultant seedlings, and also reduced the numbers of non-rhizospheric organisms with ammonification and nitrification activities. The addition of Bacillus amyloliquefaciens or Microbacterium oleovorans, at a concentration of 10⁹ colony forming units ml^?1, to the seeds significantly reduced Fusarium verticillioides count at the root inner tissues of resultant seedlings. When testing the impact of bacterial treatments on soil populations, no alterations with respect to control numbers of organisms with nitrification, ammonification or cellulolytic potentials were observed. Culturable bacterial richness and diversity calculated at the rhizoplane and root inner tissues of maize seedlings neither changed in bacterized treatments when compared to control treatment. Our study showed that the Fusarium verticillioides in vitro proven antagonists, Bacillus amyloliquefaciens and Microbacterium oleovorans (at 10⁹ colony forming units ml^?1), were also effective at greenhouse conditions without causing major changes in culturable rhizospheric and endophytic microbial richness and diversity.     

A Plant Growth-Promoting Bacterium That Decreases Nickel Toxicity in Seedlings

A plant growth-promoting bacterium, Kluyvera ascorbata SUD165, that contained high levels of heavy metals was isolated from soil collected near Sudbury, Ontario, Canada. The bacterium was resistant to the toxic effects of Ni²⁺, Pb²⁺, Zn²⁺, and CrO₄⁻, produced a siderophore(s), and displayed 1-aminocyclopropane-1-carboxylic acid deaminase activity. Canola seeds inoculated with this bacterium and then grown under gnotobiotic conditions in the presence of high concentrations of nickel chloride were partially protected against nickel toxicity. In addition, protection by the bacterium against nickel toxicity was evident in pot experiments with canola and tomato seeds. The presence of K. ascorbata SUD165 had no measurable influence on the amount of nickel accumulated per milligram (dry weight) of either roots or shoots of canola plants. Therefore, the bacterial plant growth-promoting effect in the presence of nickel was probably not attributable to the reduction of nickel uptake by seedlings. Rather, it may reflect the ability of the bacterium to lower the level of stress ethylene induced by the nickel.     

Biological Control of Fusarium spp. in Cotton, Wheat and Muskmelon by Trichoderma harzianum

A new isolate of Trichoderma harzianum (T-35) was isolated from the rhizosphere of cotton plants from a field infested with Fusarium. Under glasshouse conditions, the antagonist was applied to soil growing in a bran/peat mixture (1:1, v/v) or as a conidial suspension or used as a seed coating. When T. harzianum was tested against Fusarium oxysporum f. sp. vasinfectum, F. oxysporum f. sp. melonis or F. roseum‘Culmorum”, a significant disease reduction, was obtained in cotton, melon and wheat, respectively. Biological control of Fusarium wilt of cotton was achieved when tested at two inoculum levels of the pathogen (2 × 10⁷ and 2 × 10⁸ microconidia/kg soil), decreasing the Fusarium spp. soil population. The long term effect of T. harzianum on Fusarium wilt of cotton was studied using successive plantings. The antagonist persisted in soil throughout three consecutive plantings, reducing the Fusarium, wilt incidence in each growth cycle. At the first planting the largest amount of preparation was found superior, whereas at the third planting, no significant difference could be observed between the four rates of Trichoderma preparation. T. harzianum (T-35) controlled Fusarium wilt in cotton and muskmelon when applied in both naturally or artificially infested alluvial vertisol and sandy-loam soils, respectively. Soil or seed treatments with the antagonist provided a similar disease control of F. roseum‘Culmorum’ and of F. oxysporum f. sp. melonis.     

Management of root-knot nematode,Meloidogyne incognita and soil borne fungus,Fusarium oxysporum in cucumber using three bioagents under polyhouse conditions

Complex diseases caused by Meloidogyne incognita and Fusarium fungus in cucumber is the most destructive disease under polyhouses. The experiment was conducted in the polyhouse of the Department of Horticulture, CCS HAU, Hisar, Haryana, India during summer season (2015–16) to evaluate the potential of bacterial and fungal biocontrol agents against Meloidogyne incognita and Fusarium oxysporum f. sp. cucumerinum in cucumber. Bioagents - Trichoderma viride (Tv), Pseudomonas fluorescence (Pf), Purpureocillium lilacinum (Pl) were taken 10 and 20 g kg⁻¹ seed and bioagents liquid formulation, 10- and 15-ml kg⁻¹ seed, were mixed with the potted soil. Chemical as well as untreated check were also maintained. All the treatments significantly improved the plant growth parameter, viz., shoot length (SL), root length (RL), fresh shoot weight (FSW), fresh root weight (FRW), dry shoot weight (DSW) and dry root weight (DRW) as compared to untreated check. However, significant reduction in nematode population and maximum improvement in plant growth parameter was recorded with carbofuran followed by higher dose of bioagents liquid formulation. Among the bioagents, bioagents liquid formulation was most effective in suppressing root knot nematode galling (43 / root system) and final population in soil (131 J₂s / 200 cc soil) and fungus wilt incidence (25 %) at 30th day of after germination and significantly improved the plant growth parameters - shoot length (147.3 cm), fresh shoot weight (55.6 g), dry shoot weight (22.51 g) and dry root weight (4.50 g) from other bioagents. Bioagents liquid formulation was effective in suppression of root-knot nematode and fungus complex disease than the powder formulations of bioagents. More studies should be needed in future to evaluate the efficacy of bioagents as seed treatments and soil applications under field conditions.     

Fusarial wilt control and growth promotion of pigeon pea through bioactive metabolites produced by two plant growth promoting rhizobacteria

The bioactive metabolites produced by two plant growth promoting rhizobacteria strains, a Pseudomonas aeruginosa strain RRLJ 04 and a Bacillus cereus strain BS 03, which showed growth promotion and disease control in pigeon pea against Fusarium udum, were isolated and screened for their efficacy to control fusarial wilt of pigeon pea under gnotobiotic and nursery condition. Bioactive metabolites viz., BM 1 and BM 2 from RRLJ 04 and BM 3 from BS 03 also showed in vitro antibiosis against F. udum. Seeds treated with 50 μl seed^?1 of BM 1, 30 μl seed^?1 of BM 2 and 70 μl seed^?1 of BM 3 and grown in pathogen infested soil showed suppression of wilt disease besides growth enhancement. Per cent disease control was 90 % with BM 2 application as compared to 87 and 83 %, respectively in BM 1 and BM 3 after 90 days of growth. BM 2 treated plants were more resistant to the pathogen as compared to the other fractions tested. Mycelial dry weight was found to be reduced on treatment with the bioactive metabolites. Formation of chlamydospore-like structures was observed in the pathogen mycelium treated with BM 3. The analytical studies confirmed that two of these metabolites are phenazine derivatives.     

Quantitative changes of plant defense enzymes and phytohormone in biocontrol of cucumber Fusarium wilt by Bacillus subtilis B579

Fusarium oxysporum f. sp. cucumerinum is a destructive pathogen on cucumber (Cucumis sativus L.) seedlings and the causal organism of crown and root rot of cucumber plants. An isolate of B579, which was identified as Bacillus subtilis by 16S rDNA sequences analysis, was selected from 158 bacteria isolates as the best antagonist against F. oxysporum by dual plate assay. The production of chitinase, β-1, 3-glucanase, siderophores, indole-3-acetic acid (IAA), hydrogen cyanide (HCN), and phosphate solubilization, by B579 were screened with the selected medium by in vitro tests. The cell-free culture filtrate of B579, with a concentration of 20% (v/v), could result in the vacuolation, swelling and lysis of hyphae. Besides, it could blacken, shrunk and hindered the germination of conidia of F. oxysporum at the concentration of ≥80% (v/v). When applied as inoculants, B579 (10⁸ c.f.u. ml^?1) was able to reduce disease incidence by 73.60%, and promote seedling growth in pot trial studies. The activities of plant defense-related enzyme, peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) were significantly increased in plants treated with B579. Interestingly, a higher content of IAA, an important plant growth regulator, was detected in B579 treated plants. Furthermore, seed-soaking with B579 exhibited a better biological control effect (Biocontrol effect 73.60%) and plant growth promoting ability (Vigor Index 4,177.53) than root-irrigation (50.88% and 3,575.77, respectively), suggesting the potential use of B579 as a seed-coating agent.     

Production of methyl sulfide and dimethyl disulfide from soil-incorporated plant materials and implications for controlling soilborne pathogens

Soil-incorporated plant materials have been associated with reduction in soilborne pathogens and diseases. Mechanisms of the biocidal actions are complex and not well understood. A glasshouse experiment, a non replicated field demonstration, and a field experiment were conducted to determine volatile compounds after incorporation of various plant species and their effect on pest control. Cabbage (Brassica oleracea), canola (Brassica rapa), kale (Brassica oleracea var. acephala), lettuce (Lactuca sativa var. valmaine), two mustard varieties -Caliente (Brassica juncea) and Green wave (Brassica juncea), two radish varieties - Oil seed (Raphanus sativus var. oleiformis) and Cherriette (Raphanus sativus), common rye (Secale cereale), and sorghum Sudan grass (Sorghum bicolor var. sudanese) were used in the glasshouse experiment. Caliente 199 mustard (Brassica hirta) was planted in the field demonstration and white mustard (Sinapis alba) was used in the field experiment. Fresh plant materials were chopped manually in the glasshouse experiment and mechanically in the field studies at the flowering stage before incorporation in natural field soils. In the glasshouse experiment, the equivalent biomass dry weight ranged from a minimum of 573 g?m^?2 for L. sativa var. valmaine to a maximum of 1851 g?m^?2 for S. bicolor var. sudanese. The average biomass was 792 g?m^?2 for B. hirta and 804 g?m^?2 for S. alba in the two field studies, respectively. The glasshouse experiment used a loamy sand field soil inoculated with a natural fine sandy loam soil that was known to contain high populations of Verticillium dahliae. Soils at both field sites belonged to the sandy loam series, and efforts were made to maintain sufficient soil moisture for plant growth. Although the interest was to determine all volatile compounds in general, only methyl sulfide and dimethyl disulfide were identified and subsequently quantified. Depending on plant species and time of sampling (one to seven days after soil incorporation), 2.7 to 346.4?μg g ^?1 plant dry weight for methyl sulfide and 0 to 283.2?μg g ^?1 plant dry weight for dimethyl disulfide were found in the glasshouse experiment. In general, high concentrations of dimethyl disulfide and methyl sulfide appeared to have reduced V. dahliae colony counts in bioassay potato stem saps in the glasshouse experiment. However, the correlation was weak (R ² ?=?0.31), but a relatively stronger correlation was obtained (R ² ?=?0.58) when excluding B. oleracea and B. rapa from the regression. Dimethyl disulfide and methyl sulfide were nearly non-detectable in the field demonstration, consequently no disease assessment was made. In the field experiment, a production of 5.2?μg g ^?1 plant dry weight for methyl sulfide and 1.2?μg g ^?1 dry weight for dimethyl disulfide was found two days after soil incorporation of S. alba. Compared to the untreated control, total Fusarium oxysporum counts in field soil were significantly lower 39 days after S. alba incorporation. However, no significant impact was found on total Pythium counts. Soil population of citrus nematode (Tylenchulus semipenetrans) in the S. alba plots was significantly reduced to similar levels found in the untreated control 112 days after S. alba incorporation. Compared to the untreated control, soil density of non plant parasitic freeliving nematodes was higher 39 days after S. alba incorporation. The study demonstrated quantifiable production of methyl sulfide and dimethyl disulfide gases from a variety of plant species in glasshouse and natural field environments. Some beneficial effects against V. dahliae, F. oxysporum, and T. semipenetrans were observed. Additional studies are needed to further elucidate these complex chemical and biological interactions.     

Application of Pantoea agglomerans strain Z01 to control Fusarium wilt and its effect on the quality parameters of rockets

An antagonistic bacterium, denoted as strain Z01, was isolated from suppressive soils and identified using fatty acid profile analysis and molecular tools. Its efficacy to control Fusarium oxysporum f. sp. conglutinans on rockets (cv. Eruca sativa) was investigated in the presence of the pathogen, and its effects on the growth and pigment contents of rockets, including the plant biomass and chlorophyll and carotenoid contents, were evaluated in the absence of the pathogen. Z01 was identified as Pantoea agglomerans (GenBank accession number is JX257179). Rockets were grown under greenhouse conditions for 21 days at 25 °C and 95 % relative humidity. When the antagonist suspension was applied at 10⁸, 10⁷ and 10⁶ cells/ml by root-dipping for 20 min before transplanting, the disease incidence was 23.5 %, 28.5 % and 60.0 %, respectively. The disease incidence of rockets treated with carbendazim was 22.5 %, and in the inoculated control, the disease incidence was 82.0 %. In the absence of the pathogen, compared with the average plant biomass (10.7 g/4 plants) of the uninoculated control, application of the antagonist at 10⁸ or 10⁷ cells/ml significantly increased the biomass of the rockets by 40.9 % and 39.1 %, respectively, suggesting that Z01 had an additional ability to promote plant growth beyond its role in Fusarium wilt control. This study indicated that P. agglomerans Z01 has a potential to control Fusarium wilt in rockets. This report is the first to describe the application of P. agglomerans to control Fusarium wilt.     

Linking Belowground Carbon Allocation to Anaerobic CH4 and CO2 Production in a Forested Peatland,New York State

Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple (Acer rubrum) forest on deep peat soil. Direct measurements of CH₄ and CO₂ fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m^{? 2} s^{? 1} for CO₂ and 0.58 nmol m^{? 2} s^{? 1} for CH₄ (371 to 403 g C m^{? 2} year^{? 1}). Carbon in aboveground litter (144 g C m^{? 2} year^{? 1}) was 84% greater than C in root production (78 g C m^{? 2} year^{? 1}). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m^{? 2} year^{? 1}. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal.