Interactions Between Plant Growth Promoting Fungi and Arbuscular Mycorrhizal Fungus Glomus Mosseae and Induction of Systemic Resistance to Anthracnose Disease in Cucumber

Cucumber plants were treated with plant growth promoting fungi (PGPF), Phoma sp. (isolates GS8-2 and GS8-3) and Penicillium simplicissimum (isolate GP17-2) with or without the arbuscular mycorrhizal fungus (AMF) Glomus mosseae. Induction of systemic resistance in cucumber against the anthracnose disease caused by Colletotrichum orbiculare was tested to evaluate the nature of the interaction between the PGPF and AMF. Root colonizing ability of each fungal species as influenced by their interaction was also evaluated. Plant roots were pre-inoculated with each PGPF isolate and/or G. mosseae for four weeks and leaves were then challenge inoculated with the pathogen C. orbiculare. Plants treated with each PGPF isolate showed considerable protection against the disease, but the treatment of G. mosseae had no significant effect on disease development. However, combined inoculation of Phoma GS8-2 or GS8-3 with G. mosseae reduced the level of disease protection induced by single inoculation of each Phoma isolate. In contrast, the high levels of protection induced by the P. simplicissimum GP17-2 were not altered by combining it with G. mosseae. Root colonization of both Phoma sp. isolates was also suppressed by the presence of the G. mosseae, but such an effect was not found on the population development of P. simplicissimum. The percent cucumber root length colonized by G. mosseae was not affected by any of the PGPF isolates tested.     

Mechanism of application nursery cultivation arbuscular mycorrhizal seedling in watermelon in the field

Arbuscular mycorrhizal fungi (AMF) colonisation of plant root facilitates the absorption of nutrients such as phosphorus (P) and enhances plant biotic and abiotic resistance generally. However, arbuscular mycorrhiza (AM) colonisation decreases with application of chemical fertiliser. Here, we investigated whether AMF inoculation in nurseries would facilitate AM colonisation and take physiological and ecological functions in watermelon (Citrullus lanatus) in the field. Pot experiments were carried out to study the change of AMF colonised seedling on physiology and gene expression in nursery site. Field experiments were performed to investigate the effect of nursery AMF inoculation on yield, quality and disease resistance of watermelon in the field. The results showed that nursery‐inoculated seedlings produced more dry matter and root surface area than non‐inoculated seedlings. Expression of the secretory purple acid phosphatase (PAP) genes ClaPAP10 and ClaPAP26 was up‐regulated following AMF colonisation. Accordingly, acid phosphatase activities at the root surface and P concentrations in seedling were enhanced. After transplantation to the field, the shoot dry matter and P concentration in old stem were higher in the nursery AMF inoculated seedlings than that in non‐AMF inoculated seedling. AMF inoculation also induced increase of yields and decrease of wilt disease indexes and soluble sugar content. In addition, acid phosphatase activities and AMF spore densities were increased by nursery‐inoculation in watermelon rhizosphere soil in the field. In conclusion, nursery colonisation AMF seedling enhanced watermelon growth and yield by improving the root growth and P acquisition in nursery cultivating stage, as well as optimised soil properties in the field. Nursery cultivation of watermelon seedling with AMF was an effective technique to reduce wilt disease in continuous cropped management in watermelon.     

Biological control of Fusarium wilt of tomato with <Emphasis Type="Italic">Fusarium equiseti</Emphasis> GF191 in both rock wool and soil systems

The plant growth-promoting fungus (PGPF) Fusarium equiseti GF191 was tested for its ability to control Fusarium wilt of tomato (FWT) caused by Fusarium oxysporum f. sp. lycopersici (FOL) in both a hydroponic rock wool and soil system. F. equiseti effectively controlled FWT, with protective effects based on disease severity of 66.7–88.6% in four experiments. The numbers of colony-forming units of FOL per gram fresh weight of stems were significantly reduced (P < 0.05) in plants treated with F. equiseti. Stem extracts from F. equiseti-treated and pathogen-challenged plants significantly inhibited the germination and germ-tube length of FOL microconidia and the production of FOL budding-cells. Tomatine content in tomato stems treated with F. equiseti was significantly increased compared with the non-treated control.     

Plant Growth‐promoting Fungus Penicillium oxalicum Enhances Plant Growth and Induces Resistance in Pearl Millet Against Downy Mildew Disease

Plant Growth‐promoting Fungus (PGPF) Penicillium oxalicum was isolated from rhizosphere soil of pearl millet and was tested for its ability to promote growth and induce systemic resistance in pearl millet against downy mildew disease. The fungal isolate P. oxalicum UOM PGPF 16 was identified as P. oxalicum using ITS sequencing and morphological analysis and sequence was deposited at NCBI with accession number KF150220. Pearl millet susceptible seeds were treated with three different inducers (CS, CF and LCF) of PGPF P. oxalicum and all the inducers significantly reduced the downy mildew disease and enhanced plant growth. Among the inducers tested, CS treatment recorded highest seed germination of 91% and 1427 seedling vigour followed by LCF and CF treatments. The vegetative growth parameter and NPK uptake studies under greenhouse conditions revealed that the CS treatment of P. oxalicum remarkably enhanced the parameters tested when compared to control plants. A significant disease protection of 62% and 58% against downy mildew disease was observed in plants pretreated with CS of P. oxalicum under greenhouse and field conditions, respectively. The spatio‐temporal studies revealed that inducers P. oxalicum required a minimum of 3 days for developing maximum disease resistance which was maintained thereafter. The maximum Peroxidase (POX) activity (62.7 U) was observed at 24 h in seedlings treated with CS of PGPF P. oxalicum and the activity gradually reduced at later time points after pathogen inoculation. Chitinase (CHT) activity was significantly higher in inducer treated seedlings when compared to control seedlings inoculated with pathogen after 48 h and remained constant at all time points.     

Functional, genetic and chemical characterization of biosurfactants produced by plant growth-promoting Pseudomonas putida 267

Aims: Plant growth‐promoting Pseudomonas putida strain 267, originally isolated from the rhizosphere of black pepper, produces biosurfactants that cause lysis of zoospores of the oomycete pathogen Phytophthora capsici. The biosurfactants were characterized, the biosynthesis gene(s) partially identified, and their role in control of Phytophthora damping‐off of cucumber evaluated. Methods and Results: The biosurfactants were shown to lyse zoospores of Phy. capsici and inhibit growth of the fungal pathogens Botrytis cinerea and Rhizoctonia solani. In vitro assays further showed that the biosurfactants of strain 267 are essential in swarming motility and biofilm formation. In spite of the zoosporicidal activity, the biosurfactants did not play a significant role in control of Phytophthora damping‐off of cucumber, since both wild type strain 267 and its biosurfactant‐deficient mutant were equally effective, and addition of the biosurfactants did not provide control. Genetic characterization revealed that surfactant biosynthesis in strain 267 is governed by homologues of PsoA and PsoB, two nonribosomal peptide synthetases involved in production of the cyclic lipopeptides (CLPs) putisolvin I and II. The structural relatedness of the biosurfactants of strain 267 to putisolvins I and II was supported by LC‐MS and MS‐MS analyses. Conclusions: The biosurfactants produced by Ps. putida 267 were identified as putisolvin‐like CLPs; they are essential in swarming motility and biofilm formation, and have zoosporicidal and antifungal activities. Strain 267 provides excellent biocontrol activity against Phytophthora damping‐off of cucumber, but the lipopeptide surfactants are not involved in disease suppression. Significance and Impact of the Study: Pseudomonas putida 267 suppresses Phy. capsici damping‐off of cucumber and provides a potential supplementary strategy to control this economically important oomycete pathogen. The putisolvin‐like biosurfactants exhibit zoosporicidal and antifungal activities, yet they do not contribute to biocontrol of Phy. capsici and colonization of cucumber roots by Ps. putida 267. These results suggest that Ps. putida 267 employs other, yet uncharacterized, mechanisms to suppress Phy. capsici.     

Mixtures of plant growth-promoting rhizobacteria for induction of systemic resistance against multiple plant diseases

Studies of induced systemic resistance using strains of plant growth-promoting rhizobacteria (PGPR) have concentrated on the use of individual PGPR as inducers against multiple diseases of a single crop. To date, few reports have examined the potential of PGPR strain mixtures to induce systemic resistance against diseases of several different plant hosts. The objective of this study was to select mixtures of compatible PGPR strains with the capacity to elicit induced systemic resistance in four hosts. The specific diseases and hosts tested in this study included: bacterial wilt of tomato (Lycopersicon esculentum) caused by Ralstonia solanacearum, anthracnose of long cayenne pepper (Capsicum annuum var. acuminatum) caused by Colletotrichum gloeosporioides, damping off of green kuang futsoi (Brassica chinensis var. parachinensis) caused by Rhizoctonia solani, and cucumber mosaic virus (CMV) on cucumber (Cucumis sativus). To examine compatibility, seven selected PGPR strains were individually tested for in vitro antibiosis against all other PGPR strains and against three of the tested pathogens (R. solanacearum, C. gloeosporioides, and R. solani). No in vitro antibiosis was observed among PGPR strains or against pathogens. Twenty-one combinations of PGPR and seven individual PGPR were tested in the greenhouse for induced resistance activity. Results indicated that four mixtures of PGPR and one individual strain treatment significantly reduced the severity of all four diseases compared to the nonbacterized control: 11 mixtures reduced CMV of cucumber, 16 mixtures reduced bacterial wilt of tomato, 18 mixtures reduced anthracnose of long cayenne pepper, and 7 mixtures reduced damping off of green kuang futsoi. Most mixtures of PGPR provided a greater disease suppression than individual PGPR strains. These results suggest that mixtures of PGPR can elicit induced systemic resistance to fungal, bacterial, and viral diseases in the four hosts tested.     

Rhizobacteria that produce auxins and contain 1‐amino‐cyclopropane‐1‐carboxylic acid deaminase decrease amino acid concentrations in the rhizosphere and improve growth and yield of well‐watered and water‐limited potato (Solanum tuberosum)

Plant‐growth‐promoting rhizobacteria (PGPR) utilise amino acids exuded from plant root systems, but hitherto there have been no direct measurements of rhizosphere concentrations of the amino acid 1‐amino‐cyclopropane‐1‐carboxylic acid (ACC) following inoculation with PGPR containing the enzyme ACC deaminase. When introduced to the rhizosphere of two potato (Solanum tuberosum) cultivars (cv. Swift and cv. Nevsky), various ACC deaminase containing rhizobacteria (Achromobacter xylosoxidans Cm4, Pseudomonas oryzihabitans Ep4 and Variovorax paradoxus 5C‐2) not only decreased rhizosphere ACC concentrations but also decreased concentrations of several proteinogenic amino acids (glutamic acid, histidine, isoleucine, leucine, phenylalanine, serine, threonine, tryptophan, tyrosine, valine). These effects were not always correlated with the ability of the bacteria to metabolise these compounds in vitro, suggesting bacterial mediation of root amino acid exudation. All rhizobacteria showed similar root colonisation following inoculation of sand cultures, thus species differences in amino acid utilisation profiles apparently did not confer any selective advantage in the potato rhizosphere. Rhizobacterial inoculation increased root biomass (by up to 50%) and tuber yield (by up to 40%) in pot trials, and tuber yield (by up to 27%) in field experiments, especially when plants were grown under water‐limited conditions. Nevertheless, inoculated and control plants showed similar leaf water relations, indicating that alternative mechanisms (regulation of phytohormone balance) were responsible for growth promotion. Rhizobacteria generally increased tuber number more than individual tuber weight, suggesting that accelerated vegetative development was responsible for increased yield.     

Characterisation of antagonistic Bacillus and Pseudomonas strains for biocontrol potential and suppression of damping‐off and root rot diseases

Novel strains of rhizobacteria, Pseudomonas fluorescens Pf 9A‐14, Pseudomonas sp. Psp. 8D‐45 and Bacillus subtilis Bs 8B‐1, showed broad‐spectrum antagonistic activity and provided suppression of Pythium damping‐off and root rot of cucumber. Their biocontrol potential was further investigated for suppression of additional seedling diseases of cucumber (Phytophthora capsici) and radish (Rhizoctonia solani). Bacterial strains were also characterised for production of antibiotics, metabolites, volatiles, phytohormones and lytic enzymes. Seed and pre‐plant applications of all three antagonistic bacteria as cell suspension and talc or irradiated peat formulations to the infested potting mix provided overall high level of suppression of Phytophthora damping‐off and root rot of cucumber (66–85% healthy seedlings) and relatively low level of suppression of Rhizoctonia damping‐off of radish (18–38% healthy seedlings). Bacterial treatments also resulted in higher plant fresh masses. Seed coating with irradiated peat formulation of a mixture of three bacteria resulted in superior control of Phytophthora damping‐off and root rot of cucumber and much higher plant fresh masses. The presence of genes for biosynthesis of phenazine‐1‐carboxylic acid, 2,4‐diacetylphloroglucinol, pyrrolnitrin and pyoluteorin was confirmed in Pseudomonas strains, and that of fengycin, bacillomycin, bacilysin, surfactin and iturin A in B. subtilis Bs 8B‐1. All three strains produced HCN, salicylic acid, indole‐3‐acetic acid, protease and β‐1,3‐glucanase. Both Pseudomonas strains produced siderophores and only P. fluorescens Pf 9A‐14 showed phosphate solubilisation and chitinase activity. All three strains inhibited pathogen growth by producing volatiles, and gas chromatography–mass spectrometry analysis revealed eight compounds in Pf 9A‐14, 10 in Bs 8B‐1 and 4 in Psp 8D‐45, some with known antifungal activity. The antagonistic and plant‐growth promotion activities of these strains might be due to production of antibiotics, metabolites, lytic enzymes or phytohormones.     

Carbon trading for phosphorus gain: the balance between rhizosphere carboxylates and arbuscular mycorrhizal symbiosis in plant phosphorus acquisition

Two key plant adaptations for phosphorus (P) acquisition are carboxylate exudation into the rhizosphere and mycorrhizal symbioses. These target different soil P resources, presumably with different plant carbon costs. We examined the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on amount of rhizosphere carboxylates and plant P uptake for 10 species of low‐P adapted Kennedia grown for 23 weeks in low‐P sand. Inoculation decreased carboxylates in some species (up to 50%), decreased plant dry weight (21%) and increased plant P content (23%). There was a positive logarithmic relationship between plant P content and the amount of rhizosphere citric acid for inoculated and uninoculated plants. Causality was indicated by experiments using sand where little citric acid was lost from the soil solution over 2 h and citric acid at low concentrations desorbed P into the soil solution. Senesced leaf P concentration was often low and P‐resorption efficiencies reached >90%. In conclusion, we propose that mycorrhizally mediated resource partitioning occurred because inoculation reduced rhizosphere carboxylates, but increased plant P uptake. Hence, presumably, the proportion of plant P acquired from strongly sorbed sources decreased with inoculation, while the proportion from labile inorganic P increased. Implications for plant fitness under field conditions now require investigation.     

Local soil,but not commercial AMF inoculum,increases native and non‐native grass growth at a mine restoration site

Soil communities are often degraded in mined sites, and facilitating the recovery of soil mutualists such as arbuscular mycorrhizal fungi (AMF) may assist with the restoration of native plants. At a grassland mine restoration site, I compared a commercial AMF inoculum with soil collected from beneath native grasses as a source of inoculum, as well as a control treatment. Field plots were broadcast‐inoculated and seeded with native grasses, and biomass of native and non‐native species was measured in three consecutive years. In addition, greenhouse‐grown seedlings of a native bunchgrass (Stipa pulchra) were inoculated with similar treatments, transplanted into the field, and assessed after 18 months. When broadcast inoculation was used, the local soil inoculum tended to increase non‐native grass biomass, and marginally decreased non‐native forb biomass in the second year of study, but did not significantly affect native grass biomass. Broadcast commercial inoculum had no detectable effects on biomass of any plant group. Stipa pulchra transplants had greater N content and mycorrhizal colonization, and marginally higher shoot mass and K content, when pre‐inoculated with local soil (relative to controls). Pre‐inoculation with commercial AMF increased AMF colonization of the S. pulchra transplants, but did not significantly affect biomass or nutrient content. The findings indicate that at this site, the use of local soil as an inoculum had greater effects on native and non‐native plants than the commercial product used. In order to substantially increase native grass performance, inoculation of transplanted plugs may be one potential strategy.     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

Role of ethylene signalling in growth and systemic resistance induction by the plant growth‐promoting fungus Penicillium viridicatum in Arabidopsis

The plant growth‐promoting fungi (PGPF) have long been known to improve plant growth and suppress plant diseases. The PGPF Penicillium viridicatum GP15‐1 elicited plant growth and induced systemic resistance (ISR) in Arabidopsis thaliana against Pseudomonas syringae pv. tomato DC3000 (Pst), leading to a restriction of pathogen growth and disease development. Examination of local and systemic genes indicated that GP15‐1 did not modulate the expression of any of the tested defence‐related marker genes involved in salicylic acid (SA), jasmonic acid (JA) and ethylene signalling pathways. Subsequent challenge of GP15‐1‐colonized plants with Pst bacterium primed Arabidopsis plants for enhanced activation of the JA‐inducible Atvsp (vegetative storage protein) gene at a later stage of infection. To assess the contribution of different signalling pathways in GP15‐1‐elicited plant growth and ISR, Arabidopsis genotypes implicated in SA signalling expressing the nahG transgene (NahG) or carrying disruption in NPR1 (npr1), JA signalling (jar1) and ethylene signalling (ein2) were tested. The GP15‐1‐induced plant growth and ISR were fully compromised in an ein2 mutation. Root colonization assay revealed that the inability of the ein2 mutant to express GP15‐1‐induced plant growth and ISR was not associated with reduced root colonization by GP15‐1. In conclusion, our results demonstrate the ethylene signalling pathway is involved in plant growth promotion and ISR elicitation by the PGPF P. viridicatum GP15‐1 in Arabidopsis. These results provide evidence that ethylene signalling has a substantial role in plant growth and disease resistance.     

Fusarium species on groundnut kernels and in groundnut soil

Summary A total of 17 species and varieties of Fusarium have been isolated from groundnut kernels, rhizosphere and geocarposhere and from the soil of groundnut fields in Israel.F.solani predominated in the Fusarium flora of soil, rhizosphere and fresh kernels, and in particular on stored kernels. In the geocarposhere,F. solani, F. oxysporum andF. equiseti occurred in fairly equal amounts. Fusaria made up 16.2 to 32.6 per cent of the total mycoflora of kernels, soil, rhizosphere and geocarposphere.In tests with 14 isolates from groundnuts, production of toxins inducing visible reactions on rabbit skin was strongest when cultures were kept at 24 to 30°C. Only one isolate failed to produce a toxic reaction.The mortality of seedlings induced in inoculation tests with 23 groundnut isolates ofF. oxysporum, F. solani andF. equiseti was severe (mostly averaging 20 to 40%) in tomato and eggplant, moderate (mostly 10 to 20%) in bean, cucumber, watermelon and onion, weaker in cotton and pepper, and least in maize and wheat.     

Moderating mycorrhizas: arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries

Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (?AMF) addition of unsterilized field soil. After 9–10 weeks, half the pots received 15 mg P kg^?1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant‐available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ～0.2–0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.     

Arbuscular mycorrhiza influences carbon‐use efficiency and grain yield of wheat grown under pre‐ and post‐anthesis salinity stress

• Soil salinity severely affects and constrains crop production worldwide. Salinity causes osmotic and ionic stress, inhibiting gas exchange and photosynthesis, ultimately impairing plant growth and development. Arbuscular mycorrhiza (AM) have been shown to maintain light and carbon use efficiency under stress, possibly providing a tool to improve salinity tolerance of the host plants. Thus, it was hypothesized that AM will contribute to improved growth and yield under stress conditions.
• Wheat plants (Triticum aestivum L.) were grown with (AMF+) or without (AMF?) arbuscular mycorrhizal fungi (AMF) inoculation. Plants were subjected to salinity stress (200 mm NaCl) either at pre‐ or post‐anthesis or at both stages. Growth and yield components, leaf chlorophyll content as well as gas exchange parameters and AMF colonization were analysed.
• AM plants exhibited a higher rate of net photosynthesis and stomatal conductance and lower intrinsic water use efficiency. Furthermore, AM wheat plants subjected to salinity stress at both pre‐anthesis and post‐anthesis maintained higher grain yield than non‐AM salinity‐stressed plants.
• These results suggest that AMF inoculation mitigates the negative effects of salinity stress by influencing carbon use efficiency and maintaining higher grain yield under stress.

     

The combination of arbuscular mycorrhizal fungi inoculation (Glomus versiforme) and 28‐homobrassinolide spraying intervals improves growth by enhancing photosynthesis,nutrient absorption,and antioxidant system in cucumber (Cucumis sativus L.) under salinity

Salinity is one of the major obstacles in the agriculture industry causing huge losses in productivity. Several strategies such as plant growth regulators with arbuscular mycorrhizal fungi (AMF) have been used to decrease the negative effects of salt stress. In our experiment, 28‐homobrassinolide (HBL) with spraying intervals was combined with AMF (Glomus versiforme) in cucumber cultivars Jinyou 1^# (salt sensitive) and (Changchun mici, in short, CCMC, salt tolerant) under NaCl (100 mmol/L). Studies have documented that the foliar application of HBL and AMF colonization can enhance tolerance to plants under stress conditions. However, the mechanism of the HBL spraying intervals after 15 and 30 days in combination with AMF in cucumber under salt stress is still unknown. Our results revealed that the HBL spraying interval after 15 days in combination with AMF resulted in improved growth, photosynthesis, and decreased sodium toxicity under NaCl. Moreover, the antioxidant enzymes SOD (superoxide dismutase; EC 1.15.1.1) and POD activity (peroxidase; EC 1.11.1.7) showed a gradual increase after every 10 days, while the CAT (catalase; EC 1.11.1.6) increased after 30 days of salt treatments in both cultivars. This research suggests that the enhanced tolerance to salinity was mainly related to elevated levels of antioxidant enzymes and lower uptake of Na⁺, which lowers the risk of ion toxicity and decreases cell membrane damage.     

Interactions between arbuscular mycorrhizae and Fusarium oxysporum f. sp. ciceris: effects on fungal development,seedling growth and wilt disease suppression in Cicer arietinum L.

The purpose of present study was to develop a management strategy based on a time effective inoculation of arbuscular mycorrhizal fungi (AMF) to mitigate the yield losses of Cicer arietinum L. due to Fusarium oxysporum f. sp. ciceris (Foc). The interactions between AMF (mycorrhizal consortium; Myc) and Foc were studied in three separate experiments in two successive years (2011 and 2012). In particular, we investigated: the effect of Myc on population density of Foc, the effect of Foc on mycorrhisation (root colonisation index and AMF spore density/50?g sand) and the interactive effects of Myc and Foc on growth, phosphorus (P) content and disease severity index of C. arietinum. Results suggested that pre-inoculating plants with AMF (Myc?+?Foc) considerably reduced Foc population density, while combined (Myc/Foc) and early inoculation of AMF (Myc?+?Foc) increased mycorrhisation, growth and P content of plants. Combined and early inoculation of AMF reduced disease severity index up to 68 and 89.5%, respectively. Thus, the results suggested that soil pretreated with AMF acted as bioprotectant against the Fusarium. In conclusion, Myc should be inoculated before transplantation of crop seedlings to the fields. However, extrapolation of the results to the real field conditions should be done with caution because of differences in growth conditions and substrate used in present study i.e. net house and sand, respectively.     

氮和土著AMF对黄瓜间作土壤酶活性及氮利用的影响

设施土壤氮（N）肥的大量不合理施用和高残留是导致作物硝态N含量超标和农业面源污染的主要因素之一。研究土著丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）与间作体系强化蔬菜对不同形态N的利用并结合土壤酶活性的反馈作用,可为设施土壤N素的高效利用和降低土壤N残留提供依据。本研究采用盆栽试验,设置黄瓜单作和黄瓜//大豆间作种植模式,不同AMF处理[不接种（NM）、接种土著AMF]和不同形态N处理[不施N（N0）、有机N（谷氨酰胺120mg/kg,ON120）、无机N（碳酸氢铵120mg/kg,ION120）],探讨了设施条件下施用不同形态N、接种土著AMF与间作大豆对黄瓜根围土壤酶活性及氮利用的影响。结果表明,与NM相比,接种土著AMF使设施黄瓜地上部、根系生物量及植株N吸收量均有不同程度的增加,根围土壤NH₄ ⁺-N、NO₃ ^--N含量呈现降低趋势。同一N处理-土著AMF条件下,间作大豆处理下的黄瓜根系菌根侵染率显著高于单作处理;间作大豆也使黄瓜植株地上部、根系生物量及N吸收量显著增加,同时显著降低了根围土壤铵态N含量。此外,间作-土著AMF条件下,ON120和ION120处理的黄瓜根围土壤脲酶活性较N0处理分别提高了30%和14%,蛋白酶和硝酸还原酶活性也呈现出相同趋势。可见,所有复合处理中,以间作体系接种土著AMF与施用适量有机N的组合明显促进了设施黄瓜生长和N素利用率。     

Alterations in Root Exudation of Intercropped Tomato Mediated by the Arbuscular Mycorrhizal Fungus Glomus mosseae and the Soilborne Pathogen Fusarium oxysporum f.sp. lycopersici

Arbuscular mycorrhizal fungi (AMF) can control soilborne diseases such as Fusarium oxysporum f.sp. lycopersici (Fol). Root exudates play an important role in plant–microbe interactions in the rhizosphere, especially, in the initial phase of these interactions. In this work, we focus on (i) elucidating dynamics in root exudation of Solanum lycopersicum L. in an intercropping system due to AMF and/or Fol; (ii) its effect on Fol development in vitro; and (iii) the testing of the root exudate compounds identified in the chromatographic analyses in terms of effects on fungal growth in in vitro assays. GC‐MS analyses revealed an AMF‐dependent increase in sugars and decrease in organic acids, mainly glucose and malate. In the HPLC analyses, an increase in chlorogenic acid was evident in the combined treatment of AMF and Fol, which is to our knowledge the first report about an increase in chlorogenic acid in root exudates of AM plants challenged with Fol compared with plants inoculated with AMF only, clearly indicating changes in root exudation due to AMF and Fol. Root exudates of AMF tomato plants stimulate the germination rate of Fol, whereas the co‐inoculation of AMF and Fol leads to a reduction in spore germination. In the in vitro assays, citrate and chlorogenic acid could be identified as possible candidates for the reduction in Fol germination rate in the root exudates of the AMF+Fol treatment because they proved inhibition at concentrations naturally occurring in the rhizosphere.     

High‐throughput sequencing provides insight into manipulated soil fungal community structure and diversity during temperate forest restoration

The process of community assembly in fungal communities is poorly understood and may have important implications for restoration. However, there is a shortage of data describing fungal community composition at various stages of restoration. This study describes how microbial inoculation with field‐collected soils or a commercial inoculum influenced fungal communities during temperate tree restoration. We utilized Illumina Mi‐Seq sequencing technology to examine fungal community structure in the rhizosphere soils of trees at the conclusion of one growing season. Inoculation treatment was found to be a significant determinant of fungal community structure in one of our three experimental tree species (Liriodendron tulipifera). We also found a marginally significant influence of inoculation method on fungal community structure in the rhizosphere soils of Quercus rubra, an ectomycorrhizal tree species. Importantly, within these taxa, the use of commercial inocula, while failing to lead to detectable abundances of the inoculated taxa, strongly influenced the resulting fungal community structure after 4 months in the field, relative to control trees that received no such inoculation. We observed lower abundances of Hebeloma, a potentially important ectomycorrhizal genera, in Quercus trees receiving the commercial inoculum compared with control trees; thus, the commercial inoculum might have unexpected consequences for fungal community assembly. Such unintended legacy effects of soil inoculation should be considered in ecological restoration. Furthermore, by taking a time series approach to sampling, high‐throughput sequencing approaches could be used to test the principles of ecological assembly theory, including legacy effects of taxa no longer detectable in the community.