Field Performance and Essential Oil Production of Mycorrhizal Rosemary in Restoration Low‐Nutrient Soils

The establishment and growth of Rosmarinus officinalis L. under field conditions in two low‐nutrient‐content soils were evaluated, as well as the effect of arbuscular mycorrhizal (AM) fungi on essential oil production. The reclamation was conducted in two experimental sites: a limestone quarry and a wasteland soil, both surrounded by Mediterranean vegetation. Mycorrhizal R. officinalis plants inoculated with different AM fungal isolates were used to revegetate the sites. Pre‐transplant inoculation with mycorrhizal fungi resulted in an increased survival of R. officinalis with similar results in both experimental areas. Mycorrhizal inoculation enhanced plant growth, increased essential oil yield and improved the establishment of plants under field conditions. The results indicate that the presence of the symbiosis can accelerate plant growth and alter the biosynthesis of secondary metabolites, thus improving the yield of medicinal plant extracts. It also confirmed the importance of selecting plant/symbiont combinations adapted to the environmental constraints of low‐nutrient‐content soils to design a successful application of mycorrhizal technology in marginal soils. Copyright © 2013 John Wiley & Sons, Ltd.     

Establishment of Retama sphaerocarpa L. seedlings on a degraded semiarid soil as influenced by mycorrhizal inoculation and sewage‐sludge amendment

A field experiment was carried out to evaluate the effectiveness of mycorrhizal inoculation with three arbuscular mycorrhizal (AM) fungi (Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge), and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and the addition of composted sewage sludge (SS) with respect to the establishment of Retama sphaerocarpa L. seedlings, in a semiarid Mediterranean area. Associated changes in soil chemical (nutrient content and labile carbon fractions), biochemical (enzyme activities), and physical (aggregate stability) parameters were observed. Six months after planting, both the addition of composted SS and the mycorrhizal‐inoculation treatments had increased total N content, available‐P content, and aggregate stability of the soil. Values of water‐soluble C and water‐soluble carbohydrates were increased only in the mycorrhizal‐inoculation treatments. Rhizosphere soil from the mycorrhizal‐inoculation treatments had significantly higher enzyme activities (dehydrogenase, protease‐BAA, acid phosphatase, and β‐glucosidase) than the control soil. In the short‐term, mycorrhizal inoculation with AM fungi was the most effective treatment for enhancement of shoot biomass, particularly with G. mosseae (about 146% higher with respect to control plants). The addition of the composted SS alone was sufficient to restore soil structural stability but was not effective with respect to improving the performance of R. sphaerocarpa plants.     

Microbial and chemical sources of phosphorus supply modulate the yield and chemical composition of essential oil of rose-scented geranium (Pelargonium species) in sodic soils

Rose-scented geranium (Pelargonium sp.) is a highly valued aromatic crop. Its growth is limited by soil salinity and sodicity stress. Arbuscular mycorrhizal (AM) fungus, phosphate-solubilizing bacteria (PSB), and P fertilizers may enhance the growth and secondary metabolism in geranium plants. In this context, a pot experiment was conducted to study the effects of PSB, AM fungi (Glomus intraradices), and P fertilizer on the yield, chemical composition of essential oil, and mineral element acquisition of geranium. The dry matter yield of shoot and essential oil yield, and mineral element (P, K, Ca, Mg, Na, Fe, Cu, and Zn) uptake in shoot tissues of geranium were significantly increased by the inoculation with AM fungi, co-inoculation with AM fungi and PSB, and P fertilization as compared to control. While the co-inoculation of geranium with AM fungi and PSB significantly enhanced the content of the monoterpenes such as citronellol, geraniol, geranial, and a sesquiterpene (10-epi-γ eudesmol), the P fertilization only enhanced the content of a sesquiterpene, 10-epi-γ eudesmol in the volatile oil. We conclude that the co-inoculation of PSB and AM fungi could be the best natural alternative to phosphate fertilizers to enhance the yield and quality of essential oil from geranium plants grown in sodic soils.     

接种菌根真菌对不同磷效率基因型大豆生长和磷吸收的影响

接种丛枝菌根真菌(AMF)能显著促进大豆生长和对磷的吸收,但不同磷效率基因型大豆对AMF接种的响应还少有报道。为探究接种AMF对不同磷效率基因型大豆生长和磷转运基因表达的影响,以磷高效大豆BX10和磷低效大豆BD2为试验材料进行盆栽试验,设置接菌和不接菌处理,对大豆干重、菌根侵染性状、氮磷养分含量、根系性状,以及菌根诱导的磷转运基因表达进行了分析。结果表明, AMF接种显著促进了大豆的磷吸收,并且接菌效果存在显著的基因型差异,接种AMF显著增加了BD2的地上部干重、磷含量以及植株总磷吸收量,但只增加了BX10的地上部磷含量和总磷吸收量,对植株地上部干重没有显著影响。无论接种与否,BD2的地上部磷含量均显著高于BX10,表明磷低效的BD2具有较高的植株体内磷转运能力。不接菌条件下,两个大豆基因型根系性状无显著差异;接种AMF后BX10的根系体积和根系平均直径均显著高于BD2。BD2的菌根生长反应(MGR)和菌根磷反应(MPR)均显著高于BX10,对菌根依赖性更高。此外,在接菌处理的BD2根系,代表菌根途径磷吸收的磷转运基因GmPT8、GmPT9和GmPT10表达均显著高于BX10;相应地,BD2的总磷吸收量也显著高于BX10。以上结果表明,接种AMF对促进磷低效大豆BD2生长和磷吸收的作用更大,这可能主要是由于BD2菌根途径的磷吸收量较高,体内磷转运效率较高。以上结果将为研究AMF接种对磷吸收的贡献提供理论依据。     

AM fungi inoculation and addition of microbially‐treated dry olive cake‐enhanced afforestation of a desertified Mediterranean site

A field experiment was carried out to compare the effectiveness of inoculation with three arbuscular mycorrhizal (AM) fungi, namely Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and the addition of Aspergillus niger‐treated dry olive cake (DOC) in the presence of rock phosphate, in increasing root nitrate reductase (NR) and acid phosphatase activities, mycorrhizal colonization, plant growth and nutrient uptake in Dorycnium pentaphyllum L. seedlings afforested in a semiarid degraded soil. Three months after planting, both the addition of fermented DOC and the mycorrhizal inoculation treatments had increased root NR activity significantly, particularly the inoculation with G. deserticola (by 75 per cent with respect to non‐inoculated plants), but they had no effect on root acid phosphatase. Mycorrhizal inoculation treatments with G. deserticola or G. mosseae on their own were even more effective than the addition of fermented DOC alone in improving the growth and (NPK) foliar nutrients of D. pentaphyllum plants. The combined treatment involving the application of microbially‐treated agrowastes and mycorrhizal inoculation with AM fungi, particularly with G. mosseae, can be proposed as a successful revegetation strategy for D. pentaphyllum in P‐deficient soils under semiarid Mediterranean conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Cyamopsis tetragonoloba L Taub inoculated with arbuscular mycorrhiza and Pseudomonas fluorescens and treated with mustard oil cake overcome Macrophomina root-rot losses

The effects of inoculation of three arbuscular mycorrhizal (AM) fungi namely, Glomus mosseae, Glomus sinuosum, and Scutellospora erythropa in addition to Pseudomonas fluorescens and treatment with mustard oil cake on root-rot disease of Cyamopsis tetragonoloba L plants caused by Macrophomina phaseolina were evaluated under polyhouse conditions for 2 years. Inoculations of an arbuscular mycorrhizal fungi (AMF) in combination with P. fluorescens and mustard oil cake showed best supporting biocontrol system against the root-rot disease besides increasing the plant height, weight, and yield. The biocontrolling efficiency of dual inoculation (AMF + P. fluorescens) was the second best combination followed by AM plus mustard oil cake. Among the three AM fungi, G. mosseae inoculations showed the best results. Different combined AMF inoculations also altered the concentrations of total soluble sugars, orthodihydric phenols, flavonols, and epicuticular wax contents in host plants.     

Effects of Arbuscular Mycorrhizal Inoculation and Phosphorus Application on Yield and Nutrient Uptake of Yam

To be sustainable, production in the traditional yam cropping system, faced with declining soil fertility, could benefit from yam–arbuscular mycorrhizal (AM) symbiosis, which can improve nutrient uptake, disease resistance, and drought tolerance in plants. However, only limited information exists about AM colonization of yam. A pot experiment was conducted to collect information on the response of two genotypes (Dioscorea rotundata accession TDr 97/00903 and D. alata accession TDa 297) to AM inoculation (with and without) and phosphorus (P) (0, 0.05, 0.5, and 5 mg P kg^–1 soil). Factorial combinations of the treatments were arranged in a completely randomized design with four replicates. The percentage of AM colonization was significantly lowered at 5 mg P kg^–1 soil rate in mycorrhizal plants of both genotypes. TDr 97/00903 showed more responsiveness to AM inoculation than TDa 297. The greatest AM responsiveness for tuber yield (52%) was obtained at 0.5 mg P kg^–1 soil rate for TDr 97/00903. Mycorrhizal inoculation significantly increased root dry weight and tuber yield of TDr 97/00903 with the greatest values obtained at the 0.5 mg P kg^–1 soil rate. Arbuscular mycorrhizal inoculation did not lead to significant (P < 0.05) changes in root length and area. Phosphorus application significantly increased the shoot dry weight and root diameter of TDa 297. Uptake of P was greatest at 0.5 mg P kg^–1 soil in both genotypes and was significantly influenced by AM inoculation. Nitrogen (N) and potassium (K) uptake were greatest in mycorrhizal plants at 0.05 mg P kg^–1 soil for TDr 97/00903 but at 0.5 mg P kg^–1 soil of nonmycorrhizal plants of TDa 297. The increased tuber yield and nutrient uptake observed in the mycorrhizal plants indicate the potential for the improvement of nutrient acquisition and tuber yield through AM symbiosis.     

DO MAIZE AND PEPPER PLANTS DEPEND ON MYCORRHIZAE IN TERMS OF PHOSPHORUS AND ZINC UPTAKE?

Nutrient deficiency, especially zinc (Zn) and phosphorus (P), is a common nutritional problem for the production of some crops in Turkey. This problem results in the application of increasing amounts of several fertilizers. Mycorrhizal inoculation or the indigenous potential of mycorrhizae in the soil is a critical factor in crop production under low supply of Zn and P. The effects of selected mycorrhizal inoculation on growth and Zn and P uptake of maize and green pepper were investigated in Zn- and P-deficient calcareous soils from Central Anatolia. Soils were sterilized by autoclaving and plants were grown for 7 weeks in pots under greenhouse conditions with inoculation of two selected arbuscular mycorrhizal (AM) species (Glommus moseea and G. etunicatum) at three rates of P (0, 25, 125 mg P kg^?1 soil) and two rates of Zn (0 and 5 mg Zn kg^?1soil). Without mycorrhizal inoculation, shoot and root dry matter production were severely affected by P and Zn deficiencies, and supply of adequate amounts of P and Zn significantly enhanced plant growth. When the soil was inoculated with mycorrhizal inoculation, the increasing effects of P and Zn fertilization on plant growth remained less pronounced. In accordance with growth data, mycorrhizae inoculation enhanced P and Zn concentration of plants, especially under low supply of P and Zn. The results obtained indicate that maize and green pepper are highly mycorrizal–dependent (MD) plant species under both low P and Zn supply and mycorrhizae play an essential role in P and Zn nutrition of plants in P and Zn-deficient soils. Although addition of P and Zn increased plant growth and plants are mycorrhizal dependent on P and Zn nutrition however dependence is much more dependent on P nutrition.     

How do AMF-inoculation and supplemental irrigation affect the productivity of rainfed yellow sweet clover in agrisilviculture systems?

ABSTRACT

Yellow sweet clover (Melilotus officinalis L.) was assessed for its yield in an agri-silvicultural model of the plum (Prunus domestica (L.) cv. Opal). The treatments included two sun light exposures (morning light and afternoon light) as main plots and species of arbuscular mycorrhizal fungi (AMF) (Funneliformis mosseae, Rhizophagus irregularis and no-AMF-inoculated control) as subplots. The treatments were separately arranged for two irrigations (rainfed and supplemental irrigation) during 2016–2017. In irrigated and AMF-inoculated plants, a significant increase was observed in the performance of yellow sweet clover (dry weight and biological yield), seed nutrients (phosphorus and potassium) and weight of aerial parts in morning light conditions as much as rainfed conditions, identically for two species of fungi. In both rainfed and supplemental irrigations, the biological yield of F. mosseae inoculated plants increased by up to 23%. In supplemental irrigation, the maximum growth of plant height and relative water content were obtained from AMF-inoculated plants (R. irregularis) in afternoon light area as much as rainfed condition. In conclusion, the identical beneficial effects of mycorrhizal fungi species were enhanced by single supplemental irrigation. However, plant performance, including the quality and quantity of yield, was superior in the morning light part of each treatment.     

Effect of mixing soil saprophytic fungi with organic residues on the response of Solanum lycopersicum to arbuscular mycorrhizal fungi

The effect of the dual inoculation with arbuscular mycorrhizal (AM) and saprophytic fungi and a combination of wheat straw and sewage sludge residues were studied by determining their effect on dry weight of tomato and on chemical and biochemical properties of soil. Incubation of organic residue (sewage sludge combined with wheat straw) with saprophytic fungi and plant inoculation with mycorrhizal fungi was essential to study plant growth promotion. Soil application of organic residues increased the dry weight of tomato inoculated with Rhizophagus irregularis. The greatest shoot dry mass was obtained when the organic residues were incubated with Trichoderma harzianum and applied to AM plants. However, the greatest percentage of root length colonized with AM in the presence of the organic residues was obtained with inoculation with Coriolopsis rigida. The relative chlorophyll was greatest in mycorrhizal plants regardless of the presence of either saprophytic fungus. The presence of the saprophytic fungi increased soil pH as the incubation time increased. Soil nitrogen and phosphorus contents and acid phosphatase were stimulated by the addition of organic residues, and contents of N and P. Total N and P content in soil increased when the organic residue was incubated with saprobe fungi, but this effect decreased as the incubation period of the residue with saprobe fungi increased. The same trend was observed for soil β‐glucosidase and fluorescein diacetate activities. The application of organic residues in the presence of AM and saprophytic fungi seems to be an interesting option as a biofertilizer to improve plant growth and biochemical parameters of soils.     

Responses of phytohormones and gas exchange to mycorrhizal colonization in trifoliate orange subjected to drought stress

Phytohormones have an essential ability to adapt to abiotic stresses, including drought stress (DS), by mediating physiological and molecular processes. Arbuscular mycorrhizas (AMs) can enhance tolerance of DS, but the information regarding phytohormone changes in AM plants exposed to DS is little known. Trifoliate orange (Poncirus trifoliata) seedlings colonized by an AM fungus Funneliformis mosseae were subjected to DS and well-watered for 6 weeks. Plant growth performance, gas exchange, indole-acetic acid (IAA), gibberellins (GAs), brassinosteroids (BRs), abscisic acid (ABA), methyl jasmonate (MeJA) and zeatin riboside (ZR) were determined. The 6-week DS treatment strongly restricted root mycorrhizal colonization. Mycorrhizal inoculation significantly increased plant growth parameters under DS, as compared with non-mycorrhizal treatment. Mycorrhizal treatment also induced significantly higher leaf-relative water content, net photosynthetic rate, transpiration rate and stomatal conductance but lower intercellular CO₂ concentration and leaf temperature under DS, compared with non-mycorrhizal treatment. Mycorrhizal plants under DS condition represented significantly higher leaf ABA, IAA, GAs, BRs and ZR levels than non-mycorrhizal plants. The study, hence, suggested that mycorrhizal inoculation induced the changes of gas exchange and endogenous phytohormone levels to enhance drought tolerance in trifoliate orange.     

Growth and nitrate reductase activity in Juniperus oxycedrus subjected to organic amendments and inoculation with arbuscular mycorrhizae

The effectiveness of reforestation programs on degraded soils in the Mediterranean region is frequently limited by a low soil availability and a poor plant uptake and assimilation of nutrients. While organic amendments can improve the nutrient supply, inoculation with mycorrhizal fungi can enhance plant nutrient uptake. A pot experiment was conducted in 2004 to study the influence of inoculation with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola Trappe, Bloss. & Menge, and G. mosseae (Nicol & Gerd.) Gerd. & Trappe) and of an addition of composted sewage sludge or Aspergillus niger–treated dry‐olive‐cake residue on plant growth, nutrient uptake, mycorrhizal colonization, and nitrate reductase (NR) activity in shoot and roots of Juniperus oxycedrus L. Six months after planting, the inoculation of the seedlings with G. intraradices or a mixture of three AM fungi was the most effective treatment for stimulating growth of J. oxycedrus. There were no differences between the two mycorrhizal treatments. All treatments increased plant growth and foliar N and P contents compared to the control plants. Mycorrhizal inoculation and organic amendments, particularly fermented dry olive cake, increased significantly the NR activity in roots.     

AM真菌对田间山银花生长、矿质营养及绿原酸含量的影响

Lonicera confusa, a traditional Chinese medicine herb for treating cold, flu, acute fever, and so forth, is often grown artificially in acidic soils and suffers from phosphorus (P) deficiency. A five-year field experiment was carried out to study the colonization rate, growth, nutrition, and chlorogenic acid content of Lonicera confusa seedlings inoculated with arbuscular mycorrhizal (AM) fungi, Glomus etunicatum and Glomus intraradices. Before transplanting into a field, both AM-inoculated and uninoculated control plants were cultured in nursery beds. In the plants inoculated with the AM fungi, the colonization rate decreased linearly with time and a greater decrease was observed in the plants inoculated with G. intraradices than with G. etunicatum, while the AM colonization increased from 0% to 12.1% in the uninoculated control plants 5 years after transplanting. Plant height, crown diameter, number of new branches, and flower yield increased significantly by AM inoculation as compared to the uninoculated control. Phosphorus concentrations in leaves and flowers increased, and plant uptake of nutrients, e.g., nitrogen (N), P, and potassium (K), was also enhanced significantly by AM inoculation. The Lonicera confusa seedlings had a better response to inoculation of G. intraradices than G. etunicatum in both growth and chlorogenic acid content in flowers. In contrast, both plant P uptake and P concentrations in leaves and flowers were similar between two fungal inoculations. The positive responses of Lonicera confusa to AM inoculation in growth, nutrient uptake, flowering, and chlorogenic acid content in flowers suggested that AM inoculation in nursery beds could promote the plant growth and increase chlorogenic acid content in flowers of Lonicera confusa when grown on acidic and P-deficient soils.     

Uptake and metabolism of nitrate in mycorrhizal plants as affected by water availability and N concentration in soil

We compare the effect of arbuscular mycorrhizal (AM) colonization and PO₄^?3 fertilization on nitrate assimilation, plant growth and proline content in lettuce plants growing under well‐watered (?0.04 MPa) or drought (?0.17 MPa) conditions. We also tested how AM‐colonization and PO₄^?3 fertilization influenced N uptake (¹⁵N) and the percentage of N derived from the fertilizer (% NdfF) by plants under a concentration gradient of N in soil. Growth of mycorrhizal plants was comparable with that of P‐fertilized plants only under well‐watered conditions. Shoot nitrogen content, proline and nitrate reductase activity were greater in AM than in P‐fertilized plants under drought. The addition of 100 μg g^?1 P to the soil did not replace the AM effect under drought. Under well‐watered conditions, AM plants showed similar (at 3 mmol N), greater (at 6 mmol N) or lesser (at 9 mmol N) %NdfF than P‐fertilized plants. Comparing a control (without AM inoculation) to AM plants, differences in % NdfF ranged from 138% (3 mmol N) to 22.6% (6 mmol N) whereas no differences were found at 9 mmol N. In comparison with P fertilization, mycorrhizal effects on %NdfF were only evident at the lowest N levels, which indicated a regulatory mechanism for N uptake in AM plants affected by N availability in the soil. At the highest N level, P‐fertilized plants showed the greatest %NdfF. In conclusion, AM symbiosis is important for N acquisition and N fertilizer utilization but this beneficial mycorrhizal effect on N nutrition is reduced under large quantities of N fertilizer.     

Arbuscular mycorrhizal fungi mitigates heavy metal toxicity adverse effects in sewage water contaminated soil on Tagetes erecta L

The aim of this experiment was to evaluate the impact of colonization with arbuscular mycorrhizal (AM) fungus Glomus constrictum on the biomass production, flower quality, chlorophyll content, macronutrients and heavy metals content of marigold (Tagetes erecta L.) planted under uncontaminated soil and watered with various rates of sewage water. Sewage water utilization significantly decreased biomass production, characters of flower, nutrient concentration and rates of mycorrhizal colonization of mycorrhizal (M) and non-mycorrhizal (NM) marigold as compared to control untreated plants especially at the higher rates, but the reduction rate was proportionally higher in non-AM treatments. Mycorrhizal plants had significantly greater yield, relative chlorophyll content, leaf area, flower quality and element (P, N, K and Mg) content compared to non-inoculated marigold plants irrigated with or without sewage water. Furthermore, AM inoculation had highly decreased heavy metal (Zn, Co, Mn, Cu) content in tissues as compared to equivalent non-inoculated plants grown under sewage water application. Growing marigold with AM inoculum can reduce toxicity of heavy metals and enhance biomass production and P uptake. The results support the view that AM have a protective function for the host plant, hence playing a potential function in soil polluted immobilization processes, and thus are of assessing the potential of phytoremediation of heavy metals in sewage water contaminated soil.     

Effectiveness of two arbuscular mycorrhizal fungi on concentrations of essential oil and artemisinin in three accessions of Artemisia annua L.

A field experiment was conducted to study and compare the effectiveness of two arbuscular mycorrhizal fungi (AMF), Glomus macrocarpum (GM) and Glomus fasciculatum (GF) on three accessions of Artemisia annua. The AM inoculation significantly increased the production of herbage, dry weight of shoot, nutrient status (P, Zn and Fe) of shoot, concentration of essential oil and artemisinin in leaves as compared to non-inoculated plants. The extent of growth, nutrient concentration and production of secondary plant metabolites varied with the fungus–plant accession combination. The mycorrhizal dependency of the three accessions was related to the shoot: root ratio. Comparing the two fungal inoculants in regard to increase in essential oil concentration in shoot, the effectiveness of GF was more than that of GM. While in two accessions, GM was more effective in enhancing artemisinin concentration than GF. Increase in concentration of essential oil was found to be positively correlated to P-status of the plant. Conversely, no correlation was found between shoot-P and artemisinin concentration.     

Effect of arbuscular mycorrhizal colonization of four species of glomus on physiological responses of maize

This greenhouse study aimed to analyze the impact of arbuscular mycorrhizal (AM) fungal associations on maize (Zea mays L. hybrid Pioneer 3905) in order to compare their functional compatibility and efficiency. The AM fungus species used for this study were Glomus aggregatum, G. etunicatum, G. mosseae, and G. versiforme. Shoot and leaf masses, chlorophyll, soluble protein, total and reducing sugar, carbon (C), and nitrogen (N) concentrations, and glutamine synthetase (GS) activity in the maize leaves were analyzed. The root colonization ranged from 26% to 72% depending on the AM fungus species. Leaf mass was significantly higher when maize plants were colonized with G. etunicatum in comparison to the non‐AM control. The mycorrhizal effect on dry leaf mass ranged from 15.9% to 23.9% depending on the AM species. However, the total shoot mass did not differ significantly among the treatments. The mycorrhizal treatment had a marginally significant effect on the chlorophyll concentrations in maize leaves. The protein concentration was the highest in the plants colonized with G. etunicatum and the N percentage was significantly higher in the leaves of plants colonized by G. versiforme or G. aggregatum than those with G. mosseae. However, the AM colonization did not significantly alter the GS activity among the treatments. The highest sugar concentrations were detected in the leaves of plants colonized by G. versiforme. The sugar concentrations as well as the C percentage were lower in the leaves of plants colonized by G. etunicatum compared to the other mycorrhizal treatments but the values were comparable to the non‐AM control. Our overall results suggest that the expression of the mycorrhizal potential in the maize host plants varies among AM fungal species.     

Interaction between Alternaria alternata or Fusarium equiseti and Glomus mosseae and its effects on plant growth

The effect of inoculation with the saprophytic fungi Alternaria alternata or Fusarium equiseti on maize (Zea mays) and lettuce (Lactuca sativa) with or without arbuscular mycorrhizal (AM) colonization by Glomus mosseae was studied in a greenhouse trial. Plant dry weights of non-AM-inoculated maize and lettuce were unaffected by the presence of A. alternata and F. equiseti. In contrast, A. alternata and F. equiseti decreased plant dry weights and mycorrhization when inoculated to the rhizosphere before G. mosseae. The saprophytic fungi inoculated 2 weeks after G. mosseae did not affect the percentage of root length colonized by the AM endophyte, but did affect its metabolic activity assessed as succinate dehydrogenase activity. Although F. equiseti inoculated at the same time as G. mosseae did not affect mycorrhization of maize roots, its effect on AM colonization of lettuce roots was similar to that with A. alternata. In the rhizosphere of both plants, the population of saprophytic fungi decreased significantly, but was not affected by the presence of G. mosseae. Our results suggest that there may have been a direct effect of the saprophytic fungi on the mycorrhizal fungi in the extramatrical phase of the latter, and when the AM fungus was established in the root the AM fungus was less affected by the saprophytic fungi. Received: 16 January 1996     

Influences of a root-lesion nematode, Pratylenchus coffeae, and two arbuscular mycorrhizal fungi, Acaulospora mellea and Glomus clarum on coffee (Coffea arabica L.)

A greenhouse experiment was conducted to investigate the effects of a root-lesion nematode, Pratylenchus coffeae, two arbuscular mycorrhizal (AM) fungi, Acaulospora mellea and Glomus clarum, and timing of inoculation on the growth and nutrition of a nematode-susceptible Arabica coffee cultivar. The late AM inoculation (added simultaneously with nematodes) did not enhance coffee tolerance to P. coffeae. In the presence of P. coffeae, late-mycorrhizal plants were P deficient during the entire experiment and their foliar P concentration remained as low as that of non-mycorrhizal plants. After 7.5 months, nematodes decreased AM colonization of late-mycorrhizal plants by half and their biomass was only 20–30% that of the controls. In contrast, early AM inoculation (4 months before nematode inoculation) with either AM species improved the tolerance of coffee to P. coffeae. Root colonization by AM was not significantly reduced by P. coffeae. Despite higher densities of nematodes, root lesions were less numerous and more localized in early AM inoculated plants than in those of non-mycorrhizal plants. In the presence of P. coffeae, early AM-inoculated plants remained P sufficient and their biomass was still 75–80% that of their nematode-free controls. This study shows that in soils with low P levels, enhanced tolerance to P. coffeae seems limited to mycorrhizal coffee plants with well established AM symbiosis and improved P status. Received: 11 March 1997     

Changes in biological activity of a degraded Mediterranean soil after using microbially-treated dry olive cake as a biosolid amendment and arbuscular mycorrhizal fungi

A field experiment was carried out to assess the effect of a combined treatment involving addition of Aspergillus niger-treated dry olive cake (DryOC) in the presence of rock phosphate, plus pre-transplant inoculation of seedlings with the arbuscular mycorrhizal (AM) fungi Glomus intraradices, Glomus deserticola or Glomus mosseae, on the establishment of Dorycnium pentaphyllum L., in a degraded semiarid Mediterranean area. Associated changes in soil labile C fractions, enzyme activities and aggregate stability were also observed. One year after planting, the combined treatment of fermented DryOC addition and inoculation with AM fungi, particularly with G. mosseae (on average 328% greater than control plants), had the strongest effect on the shoot biomass of D. pentaphyllum. Only the fermented DryOC addition increased assimilable P, total N and aggregate stability, the greatest increase being in the soil available P content (about four-fold higher than in the non-amended soil). Both the addition of fermented DryOC and the mycorrhizal inoculation treatments significantly increased enzyme activities of rhizosphere soil (dehydrogenase, protease-BAA, acid phosphatase and β-glucosidase). The microbially-treated DryOC proved to be an effective amendment for improving the soil quality which, in turn, enhanced the success of revegetation with mycorrhizal D. pentaphyllum seedlings.