Nickel-tolerant Brevibacillus brevis and arbuscular mycorrhizal fungus can reduce metal acquisition and nickel toxicity effects in plant growing in nickel supplemented soil

The growth of clover (Trifolium repens ) and its uptake of N, P and Ni were studied following inoculation of soil with Rhizobium trifolii, and combinations of two Ni-adapted indigenous bacterial isolates (one of them was Brevibacillus brevis) and an arbuscular mycorrhizal (AM) fungus (Glomus mosseae). Plant growth was measured in a pot experiment containing soil spiked with 30 (Ni I), 90 (Ni II) or 270 (Ni III) mg kg⁻¹ Ni-sulphate (corresponding to 11.7, 27.6 and 65.8 mg kg⁻¹ available Ni on a dry soil basis). Single inoculation with the most Ni-tolerant bacterial isolate (Brevibacillus brevis) was particularly effective in increasing shoot and root biomass at the three levels of Ni contamination in comparison with the other indigenous bacterial inoculated or control plants. Single colonisation of G. mosseae enhanced by 3 fold (Ni I), by 2.4 fold (Ni II) and by 2.2 fold (Ni III) T. repens dry weight and P-content of the shoots increased by 9.8 fold (Ni I), by 9.9 fold (Ni II) and by 5.1 fold (Ni III) concomitantly with a reduction in Ni concentration in the shoot compared with non-treated plants. Coinoculation of G. mosseae and the Ni-tolerant bacterial strain (B. brevis) achieved the highest plant dry biomass (shoot and root) and N and P content and the lowest Ni shoot concentration. Dual inoculation with the most Ni-tolerant autochthonous microorganisms (B. brevis and G. mosseae) increased shoot and root plant biomass and subtantially reduced the specific absorption rate (defined as the amount of metal absorbed per unit of root biomass) for nickel in comparison with plants grown in soil inoculated only with G. mosseae. B. brevis increased nodule number that was highly depressed in Ni I added soil or supressed in Ni II and Ni III supplemented soil. These results suggest that selected bacterial inoculation improved the mycorrhizal benefit in nutrients uptake and in decreasing Ni toxicity. Inoculation of adapted beneficial microorganisms (as autochthonous B. brevis and G. mosseae) may be used as a tool to enhance plant performance in soil contaminated with Ni.     

Possible influence of Rhizobium on VA mycorrhiza metabolic activity in double symbiosis of alfalfa plants (Medicago sativa L.) grown in a pot experiment

Summary Alfalfa (Medicago sativa, L. cv Aragón) plants were grown under greenhouse conditions in pots of inert sand and vermiculite. The plants were inoculated with Rhizobium meliloti strain 102F28, with Glomus fasciculatus or with a mixture of both microorganisms. Plants inoculated with both Rhizobium and Glomus had the highest shoot dry weight and the lowest root-to-shoot ratio. Roots from dually inoculated plants also had a higher oxygen uptake and nodule nitrogenase activity than those from plants inoculated with either of the two microsymbionts alone. However, the dry weight of the roots from only VAM-infected plants was higher than those from Rhizobium or from Rhizobium plus Glomus-inoculated ones. These differences did not correlate with succinate dehydrogenase activity, which was similar between treatments. Nutrient element concentrations were increased in dually infected plants in comparison with those of plants inoculated with only Rhizobium or Glomus. These data suggest that Rhizobium may affect fungal metabolism and that the effect is not achieved via the tricarboxylic acid pathway.     

Biologically-induced hydrolysis of parathion in soil: Isolation of hydrolyzing bacteria

Fifty bacterial isolates from a parathion-treated soil (Gilat, Israel) were tested for their ability to hydrolyze the organophosphorus insecticide, parathion in peptone-yeast extract medium. After 5 days 33 isolates had hydrolyzed at least a portion of the added parathion. Eight of these isolates hydrolyzed 75% of the added parathion in 5 days and appeared to be Bacillus strains. Ten of these 33 isolates had hydrolyzed all of the parathion after 5 days and appeared to be Arthrohacter strains. One isolate from each group was tested further. During the logarithmic phase of growth, Bacillus sp., isolate 10, hydrolyzed less than 10% of the parathion added to peptone-yeast extract medium and was not active in parathion hydrolysis when inoculated into sterilized, parathion-treated soil. Arthrobacter sp., isolate 6, hydrolyzed parathion rapidly in peptone-yeast extract medium and in sterilized, parathion-treated soil. It used parathion or its hydrolysis product, p-nitrophenol, as sole carbon source. The parathion hydrolyzing enzyme appeared to be constitutive in isolate 6. Single applications of p-nitrophenol at concentrations greater than 1 mM inhibited growth but successive additions of smaller amounts permitted growth to continue.     

Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil

The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic (Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat (Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita, separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using ³²P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita, but not G. intraradices. By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased ³²P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices, which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway.     

Amendment of an Acid Mine Soil with Compost and Polyacrylate Polymers Enhances Enzymatic Activities but may Change the Distribution of Plant Species

Many soils derived from pyrite mines spoils are acidic, poor in organic matter and plant nutrients, contaminated with trace elements, and support only sparse vegetation. The establishment of a plant cover is essential to decrease erosion and the contamination of water bodies with acid drainage containing large concentrations of trace elements. We tested the application of compost and polyacrylate polymers to promote the growth of indigenous plant species present in the mine area. Soil treatments consisted of unamended soil (control), soil with mineral fertilizers only, soil with fertilizer plus compost, soil with fertilizer plus polyacrylate polymers, and soil with fertilizer plus both amendments. Half of the soil was grown with Briza maxima L. (greater quaking grass), Chaetopogon fasciculatus (Link) Hayek (chaetopogon), and Spergularia purpurea (Persoon) G. Don fil. (purple sandspurry), while the remainder was left bare. In the absence of plants, the greatest improvements in soil conditions were obtained by the application of both amendments, which was associated with the greatest values of protease, acid phosphatase, and β-glucosidase, whereas the activity of cellulase and microbial respiration were similar in soil amended with compost or polymer. Dehydrogenase activity was greatest in soil with compost (with or without polymer), whereas urease activity was impaired by both amendments. In the presence of plants, the application of both amendments led to the greatest activities of protease, urease, β-glucosidase, cellulase, and microbial respiration, but acid phosphatase was mainly enhanced by polymer and dehydrogenase was increased by compost. Plant growth was stimulated in all treatments compared with unamended soil, but the greatest value for total accumulated biomass was obtained in fertilized soil receiving both amendments. However, species responded differently to treatment: while the growth of B. maxima was greatest in soil with compost and polymer, the growth of C. fasciculatus responded better to soil with compost, and S. purpurea grew better in polymer-amended soil. The amendments tested improved the quality of a mine soil and stimulated plant growth. However, botanical composition likely changes over time with amendments, and this needs to be considered when a large scale application of amendments is projected.     

Interactions between the arbuscular mycorrhizal fungus Glomus mosseae and plant growth-promoting fungi and their significance for enhancing plant growth and suppressing damping-off of cucumber (Cucumis sativus L.)

This study investigated the interactions between the arbuscular mycorrhizal fungus (AMF) Glomus mosseae and the plant growth-promoting fungi (PGPF) Penicillium simplicissimum GP17-2 and Trichoderma harzianum GT3-2 in relation to their colonization of roots and the rhizosphere of cucumber (Cucumis sativus L.), and their effect on plant growth and suppression of the damping-off pathogen Rhizoctonia solani. Combined inoculation of T. harzianum with G. mosseae increased the percentage of AMF root colonization, but the presence of P. simplicissimum had no significant effect on mycorrhizal formation. The existence of G. mosseae decreased the population development of T. harzianum in and/or around the roots, however, growth of P. simplicissimum was not affected. Both PGPF isolates were effective in increasing the plant shoot and root dry weight, G. mosseae, however, was not. Nevertheless, co-inoculation of G. mosseae with T. harzianum synergistically enhanced plant growth. A comparable additive effect on plant growth was not observed when P. simplicissimum was combined with G. mosseae. Treating plants with the PGPF either simultaneously with the pathogen or prior to pathogen infection suppressed damping-off disease. G. mosseae was significantly effective in reducing disease severity when inoculated prior to the pathogen but not when inoculated simultaneously with the pathogen. Interestingly, the levels of disease protection achieved by the single inoculation of P. simplicissimum, T. harzianum or G. mosseae were significantly increased by combined inoculation of each PGPF with G. mosseae.     

Selection of Leguminous Trees Associated with Symbiont Microorganisms for Phytoremediation of Petroleum-Contaminated Soil

Leguminous trees have a potential for phytoremediation of oil-contaminated areas for its symbiotic association with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi (AMF). This study selects leguminous tree associated with symbiotic microorganisms that have the potential to remediate petroleum-contaminated soil. Seven species of trees were tested: Acacia angustissima, Acacia auriculiformis, Acacia holosericea, Acacia mangium, Mimosa artemisiana, Mimosa caesalpiniifolia, and Samanea saman. They were inoculated with AMF mix and nitrogen-fixing bacteria mix and cultivated over five oil levels in soils, with five replicates. The decreasing of total petroleum hydrocarbons (TPH) values occurred especially with S. saman and its symbiotic microorganisms on highest oil soil contamination. Despite the large growth of A. angustissima and M. caesalpiniifolia on the highest level of oil, these species and its inoculated microorganisms did not reduce the soil TPH. Both plants were hydrocarbon tolerant but not able to remediate the polluted soil. In contrast were significative hydrocarbon decrease with M. artemisiana under high oil concentrations, but plant growth was severely affected. Results suggest that the ability of the plants to decrease the soil concentration of TPH is not directly related to its growth and adaptation to conditions of contamination, but the success of the association between plants and its symbionts that seem to play a critical role on remediation efficiency.     

Assessing the tolerance to heavy metals of arbuscular mycorrhizal fungi isolated from sewage sludge-contaminated soils

Different fungal ecotypes were isolated from soils which had received long-term applications of metal-contaminated sewage sludge with the aim of studying the degree of tolerance and adaptation to heavy metals of arbuscular mycorrhizal (AM) fungi. The development and structural aspects of AM colonization produced by the different fungal isolates were studied using two host plants, Allium porrum and Sorghum bicolor, which were grown in either contaminated or non-contaminated soils. Four different AM fungi were successfully isolated from the experimental field plots: (i) Glomus claroideum, isolated from plots receiving only inorganic fertilizer; (ii) another apparently similar ecotype of Glomus claroideum, but isolated from plots with 300 m³ ha⁻¹ year⁻¹ of contaminated sludge added, (iii) an unidentified Glomus sp., present only in the less contaminated plots (100 m³ ha⁻¹ year⁻¹ of unamended sludge) and (iv) Glomus mosseae, isolated from plots receiving 100 or 300 m³ ha⁻¹ year⁻¹ of amended or unamended sludge (intermediate rates of contamination). There were consistent differences in behaviour among the four AM fungi tested with regard to the colonization levels they produced in non-contaminated and contaminated soils. Both total and arbuscular colonization were affected by heavy metal contamination. The main conclusions of this study are that Glomus sp. and G. mosseae isolates are strongly inhibited by heavy metals, which acted mainly by interfering with the growth of the external mycelium, and also by limiting the production of arbuscules. Our results suggest that G. claroideum isolates, particularly the ecotype which was isolated from the plots receiving the highest dose of metal-contaminated sludge, shows a potential adaptation to increased metal concentration in soil.     

The role of inoculum identity in drought stress mitigation by arbuscular mycorrhizal fungi in soybean

It is well known that arbuscular mycorrhizal fungi (AMF) effects on plant growth largely depend on fungus identity. The objective of this study was to test whether three individual AMF isolates and their mixture mitigate drought stress (DS) differentially in soybean (Glycine max) genotype, predicting that under DS, the mixture of the AMF isolates would provide greater benefits to soybean plants than individual ones. In a greenhouse experiment, a drought-susceptible soybean genotype was inoculated with Septoglomus constrictum, Glomus sp., and Glomus aggregatum, known to be among the most abundant in agricultural and natural soils from central Argentina, and their mixture (Mx). Whereas under well-watered (WW) conditions, individual isolates and Mx treatment were similarly infective; under DS conditions, the Mx treatment showed lower rates of root colonization. Between WW and DS conditions, biomass was decreased in all treatments, although this effect was more marked in non-AM plants. Moreover, AMF strains improved water content and P and N concentrations. Under DS, the Mx treatment was unable to exceed the highest contents that were recorded by AMF isolates. However, under WW conditions, the Mx treatment showed a higher N content than individual isolates. Under both watering conditions, AM plants reduced oxidative damage evaluated as malondiadehyde and chlorophyll content and keep constant osmotic metabolites such as soluble sugars and proline content, without significant differences between AMF isolates and the Mx treatment. These results show that AMF play an important role in mitigating drought impacts on soybean, but that mixtures of AMF isolates did not perform as well as the best single strain inoculum, excluding complementarity effects and suggesting selection effect of AMF on DS alleviation in soybean.     

Growth response of field-grown Siratro (Macroptilium atropurpureum Urb.) and Aeschynomene american L. to inoculation with selected vesicular-arbuscular mycorrhizal fungi

Summary The effect of inoculation with a selected isolate of Glomus etunicatum Becker and Gerdemann and one of G. intraradices Schenck and Smith on the growth and nutrient content of Macroptilium atropurpureum Urb. cv. Siratro and Aeschynomene americana L., at applied P levels of 10, 30, 60, and 120 kg ha^-1, was studied under field conditions. At all P levels and for all harvests, the shoot dry mass of Siratro and A. americana were greater for the plants inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungi than the control plants. Differences between the VAM fungus-inoculated and the control plants were most marked between 30 and 90 kg ha^-1 of applied P and diminished at 120 kg ha^-1. At the first harvest of Siratro, the plants inoculated with G. etunicatum had a greater shoot dry mass than those inoculated with G. intraradices, for all levels of applied P. However, for subsequent harvest of Siratro and for the one harvest of A. americana the response of shoot dry mass to the two VAM fungi was equivocal. Fungal inoculation gave at least a 30% saving in the amount of P fertilizer required (40 kg ha^-1) for the maximum yield. The plants inoculated with VAM fungi had a greater tissue concentration and total content of P and N than the control plants at low and intermediate levels of applied P. The percentage of root colonized by VAM fungi for the inoculated plants of the two legumes increased linearly with P additions up to 60 kg ha^-1. The conclusion is that under amended (limed and fertilized) soil conditions, inoculation with selected VAM fungi can improve the establishement and growth of forage legumes in fields that contain ineffective populations of native VAM fungi.     

Mycorrhiza inoculation effects on seedling establishment,survival and morphological properties of Ziziphora clinopodioides Lam.

In this paper, the establishment and growth of medicinal species Ziziphora clinopodioides Lam. were studied through inoculation with two mycorrhizal fungi species, Glomus mosseae and Glomus intraradices, in arid/semi-arid Bahar-Kish rangelands, Iran in 2012 and 2013. The root colonization percentage of Ziziphora, as well as their establishment and growth were enhanced in 2013 using G. mosseae. In this year, less rainfall and higher temperature decreased the survival, growth and morphological traits of the studied plants. Growth and establishment of the inoculated plants using G. intraradices improved in 2013, while inoculation with G. mosseae showed more beneficial effects in 2012. In both years, the strain, the growth and establishment percentage of seedlings in inoculated treatments with mycorrhizal species were significantly improved. According to the results, G. intraradices mycorrhizal fungi is recommended as a biological fertilizer in increasing the forage production and the initial establishment of Ziziphora in arid and semi-arid rangelands.     

Effects of AM fungi and organic fertilizers on the reproduction of the nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> and on the growth and water loss of tomato

Glasshouse experiments were conducted to assess the influence of arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Gigaspora margarita) and organic fertilizers (cow dung, horse dung, goat dung and poultry manure) alone and in combination on the reproduction of the nematode Meloidogyne incognita and on growth and water loss of tomato. Meloidogyne incognita decreased water loss of tomato from the first week onwards after inoculation. AM fungi increased water loss of both nematode-infected and uninfected plants. Glomus mosseae was better at improving growth of tomato and reducing galling and nematode multiplication than G. margarita, but the rate of water loss was similar with both fungi. Addition of organic fertilizers improved growth of tomato, but decreased the rate of water loss. There was less galling and nematode multiplication with poultry manure, which improved tomato growth more than goat dung, while cow dung was the least effective organic fertilizer. Greatest plant growth and least nematode reproduction were observed in plants inoculated with M. incognita along with G. mosseae and poultry manure.     

Bacterial inoculants for rice: effects on nutrient uptake and growth promotion

Beneficial soil bacteria are able to colonize plant root systems promoting plant growth and increasing crop yield and nutrient uptake through a variety of mechanisms. These bacteria can be an alternative to chemical fertilizers without productivity loss. The objectives of this study were to test bacterial inoculants for their ability to promote nutrient uptake and/or plant growth of rice plants subjected to different rates of chemical fertilizer, and to determine whether inoculants could be an alternative to nitrogen fertilizers. To test the interaction between putatively beneficial bacteria and rice plants, field experiments were conducted with two isolates: AC32 (Herbaspirillum sp.) and UR51 (Rhizobium sp.), and different nitrogen fertilization conditions (0%, 50%, and 100% of urea). Satisfactory results were obtained in relation to the nutrient uptake by plants inoculated with both isolates, principally when the recommended amount of nitrogen fertilizer was 50% reduced. These bacterial strains were unable to increase plant growth and grain yield when plants were subjected to the high level of fertilization. This study indicated that the tested inoculant formulations can provide essential nutrients to plants, especially when the levels of nitrogen fertilizers are reduced.     

Use of mycorrhizal seedlings on recovery of mined dunes in northeastern Brazil

The exploitation of minerals from coastal dunes in northeastern Brazil requires subsequent revegetation for ecosystem recovery. In mined dunes areas, we have compared the growth of Guazuma ulmifolia and Tabebuia roseo-alba seedlings using substrates containing 10 or 15% of cattle manure, uninoculated or inoculated with a mixture of native arbuscular mycorrhizal fungi (AMF) or exotic AMF (Acaulospora longula). The inoculated plants had a higher percentage of colonization than those that were uninoculated. Plants of G. ulmifolia had the highest growth when inoculated with native AMF and fertilized with 10% manure or inoculated with A. longula and fertilized with 15% manure. In general, fertilization with 15% manure did not produce greater seedling development and had a negative effect on the effectiveness of the symbiosis. Twenty one AMF species were recorded in the planting areas at the end of the experiments, with a predominance of species that form acaulosporoid spores in areas with T. roseo-alba and gigasporoid spores in areas with G. ulmifolia plants. The incorporation of 10% cattle manure and native AMF in the substrate of T. roseo-alba and G. ulmifolia seedlings contributes to the initial establishment of plants in the field and to the incorporation of AMF propagules in the soil of the revegetated mined dunes.     

Effects of Arbuscular Mycorrhizal Fungi on Growth and Yield of Cucumber Plants

Abstract

In two pot experiments, cucumber (Cucumis sativus L. cv. Jinlu No. 3) seedlings were each inoculated with one of three arbuscular mycorrhizal fungi (AMF), Glomus mosseae, Glomus intraradices, or Glomus versiforme, or uninoculated. Seedling growth and weight of single fruit were investigated. The results indicated that growth of seedlings was significantly enhanced by G. mosseae, inhibited by G. versiforme, and not significantly influenced by G. intraradices. The dry weight of seedlings inoculated with G. mosseae was 1.2 times its counterparts. The concentrations of nitrogen (N) and phosphorus (P) in roots and magnesium (Mg), copper (Cu), and zinc (Zn) concentration in shoots were increased by inoculating the three AMF, and potassium (K) and iron (Fe) concentrations in shoots decreased significantly. The weights of single fruit of plants preinoculated with G. mosseae and G. versiforme were about 1.4 and 1.3 times higher than those from the uninoculated treatment, respectively.     

Comparisons of vesicular-arbuscular mycorrhizal species and inocula formulations in a commercial nursery and on diverse Florida beaches

For efficient use of mycorrhizal inoculum the effectiveness of the isolate used and the rate of application required for maximum colonization must be known. The objectives of this research were to (1) define the lower limit of inoculum density required for maximum colonization of Uniola paniculata in a commercial nursery and (2) evaluate the performance of a selected native dune vesicular-arbuscular mycorrhizal (VAM) isolate versus a commercially available non-dune VAM (foreign) isolate on three diverse Florida beaches. An inoculum-dilution study was conducted in a commercial nursery with cutroot inoculum of a Glomus sp. that had been isolated from a Florida dune. Maximum colonization was achieved with approximately 1 propagule ml^-1 of growth medium. In a separate nursery study, 10 inoculation treatments (combinations of inoculum source and level) were established in the commercial nursery. Treatments included cut-root and sheared-root inoculum of the native dune isolate, and Nutri-Link, a commercial inoculum of G. intraradices. Colonized plants from selected treatments were transplanted to beach sites around Florida. At Miami Beach, after one growing season, the shoot mass of plants inoculated with the native isolate was approximately twice that of plants inoculated with the foreign isolate. At Katherine Abbey Hanna Park and Eglin Air Force Base there were no significant inoculum source effects on shoot mass or root length after one growing season. However, the native isolate produced a greater colonized root length than the foreign isolate in all plantings. The soil hyphal density was measured at Eglin Air Force Base, and the results showed that plants inoculated with the native isolate had more soil hyphae (4.33 mg^-1) than plants inoculated with the foreign isolate (3.65 mg^-1) or the non-inoculated plants (2.12 mg^-1). Even where there were no obvious shoot growth responses, mycorrhizal inoculation may have an important effect on dune stabilization, as soil hyphae are known to bind sand grains and improve dune stability.Publishedas Florida Agriculture Experiment Station Journal SeriesPublishedas Florida Agriculture Experiment Station Journal Series     

Phytotoxic effects of industrial and sewage waste waters on growth,chlorophyll content,transpiration rate and relative water content of potted sunflower plants

Waste water coming from two factories, namely Manquabad (fertilizer) and Bani Qura (detergents and oils) factory and Arab El-Madabegh sewage effluents were determined for their phytotoxicities and physicochemical properties. The effect of the waters on the growth, chlorophyll content, transpiration rate and leaf relative water content of sunflower plants was undertaken in pots. In addition, the phytotoxicity present in the waste waters on embryonic radicle growth was also studied. The experiments were repeated each month from January to June, 1992. The three waste waters exhibited significant phytotoxic effects on the radicle growth of sunflower. The phytotoxicity varied with monthly sampling. The waste water from the fertilizer factory (Manquabad) collected in February, May and June showed almost 100% inhibition on the radicle growth, while January and April sampling had a stimulatory effect. Most of the tested water exhibited significant inhibition on shoot growth. Root growth was significantly enhanced by Arab El-Madabegh sewage water collected in February, March and April and was suppressed in the other three months. The three waste waters showed inhibitory effect on chlorophyll content. The inhibition was very high in the January sampling. Chlorophyll stability to heat was significantly lower in February and March and higher in May and June water-treated plants. Generally waste water-treated plants showed a lower transpiration rate than the control (tap water). Leaf relative water content of plants grown in the waste waters was significantly lower in May and June collected water than in the other four months collections. The physicochemical analysis of the waste waters revealed that the amount of Na⁺, K⁺, Ca⁺² Zn⁺², Cu⁺², Iron, Cl^?, SO₄ ^?2 and the degree of electrical conductivity were often above the limits of the standard for irrigation water for agricultural land, and some of these properties would be severely detrimental to crop growth. Generally waste water coming from the Manquabad fertilizer factory consistently revealed the highest inhibition, Bani Qura detergents and oils factory the second and Arab El-Madabegh sewage the least.     

Colonisation of seminal roots of wheat and barley by egg-parasitic nematophagous fungi and their effects on Gaeumannomyces graminis var. tritici and development of root-rot

This study provides evidence that egg-parasitic nematophagous fungi, Pochonia chlamydosporia, Pochonia rubescens and Lecanicillium lecanii, can also reduce root colonisation and root damage by a fungal pathogen. Interactions of nematophagous fungi with the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), and their influence on severity of the root disease it causes were studied in laboratory and pot experiments. In Petri dish experiments the three nematophagous fungi reduced colonisation of barley roots by Ggt and also reduced necrotic symptoms. On the contrary, root colonisation by nematophagous fungi was unaffected by Ggt. In growth tube experiments, the three nematophagous fungi again reduced Ggt root colonisation and increased effective root length of barley seedlings. This was true for both simultaneous and sequential inoculation of nematophagous fungi versus Ggt. In the pot experiments the inoculum of the tested fungi in soil was applied in the same pot, as a mixture or in layers, or in coupled pots used for wheat grown with a split-root system. The nematophagous fungi P. chlamydosporia (isolate 4624) and L. lecanii (isolate 4629), mixed with Ggt or in split root systems with the pathogen, promoted growth of wheat (i.e. increased shoot weight), although no disease reduction was found. In split root systems, lower levels of peroxidase activity were found in seedlings inoculated with Ggt in combination with the nematophagous isolates 4624 and 4629 than when the take-all fungus was applied alone.Our results show that nematophagous fungi reduce root colonisation by Ggt, root damage and stress induced senescence in Ggt-inoculated plants.     

Effects of Kocide 101® on the bean (Phaseolus vulgaris L.)‐Rhizobium symbiosis

A glasshouse study was undertaken to investigate the effects of the copper fungicide Kocide 101 and its residues in soil on the growth, nodulation and nitrogen fixation of beans (Phaseolus vulgaris L.). The soil used was a sandy clay loam classified as Typic Rhodustalf. The bean variety SUA 90 was used as test crop. The bean rhizobia strains CIAT 899, PV, and a local isolate were used. Kocide 101 applied at the recommended rate (equivalent to 1.7 mg kg^‐1 soil) had no significant negative effects on the growth, nodulation or nitrogen fixation of bean plants. Higher levels of Kocide 101 significantly (P < 0.05) reduced plant growth, nodulation and nitrogen fixation. The bean plants inoculated with the “local isolate”; rhizobia had the highest dry matter weights, nodule numbers and nodule dry weights, and also had more N fixation. They were followed by those inoculated with the PV, strain and, lastly, those inoculated with CIAT 899. The growth and nodulation of bean plants were still curtailed by the Kocide 101 residues four months after the fungicide was first applied to the soil. Therefore, occurrence of high levels of Kocide 101 in soils can have long‐term effects on the performance of the bean‐rhizobia symbiosis.     

Isolation and identification of potassium-solubilizing bacteria from tobacco rhizospheric soil and their effect on tobacco plants

Soil potassium supplementation relies heavily on the use of chemical fertilizer, which has a considerable negative impact on the environment. Potassium-solubilizing bacteria (KSB) could serve as inoculants. They convert insoluble potassium in the soil into a form that plants can access. This is a promising strategy for the improvement of plant absorption of potassium and so reducing the use of chemical fertilizer. The objectives of this study were to isolate and characterize tobacco KSB and to evaluate the effects of inoculation with selected KSB strains on tobacco seedlings. Twenty-seven KSB strains were isolated and identified through the comparison of the 16S ribosomal DNA. Among them, 17 strains belonged to Klebsiella variicola, 2 strains belonged to Enterobacter cloacae, 2 strains belonged to Enterobacter asburiae, and the remaining 6 strains belonged to Enterobacter aerogenes, Pantoea agglomerans, Agrobacterium tumefaciens, Microbacterium foliorum, Myroides odoratimimus, and Burkholderia cepacia, respectively. All isolated KSB strains were capable of solubilizing K-feldspar powder in solid and liquid media. K. variicola occurred at the highest frequency with 18 strains. Four isolates, GL7, JM3, XF4, and XF11, were selected for a greenhouse pot experiment because of their pronounced K-solubilizing capabilities. After being treated with the four KSB strains, plant dry weight and uptake of both K and nitrogen (N) by tobacco seedlings increased significantly. These increases were higher with the combination of KSB inoculation and K-feldspar powder addition. Isolate XF11 showed the most pronounced beneficial effect on plant growth and nutrient uptake by tobacco seedlings. Combining the inoculation of KSB and the addition of K-feldspar powder could be a promising alternative to commercial K fertilizer and may help maintain the availability of soil nutrients. Further studies are necessary to determine the effects of these bacterial strains on mobilization of potassium-bearing minerals under field conditions.