Mycorrhizae, biocides, and biocontrol 3. Effects of three different fungicides on developmental stages of three AM fungi

The effects of biocide use on nontarget organisms, such as arbuscular mycorrhizal (AM) fungi, are of interest to agriculture, since inhibition of beneficial organisms may counteract benefits derived from pest and disease control. Benomyl, pentachloronitrobenzene (PCNB) and captan were tested for their effects on the germination and early hyphal growth of the AM fungiGlomus etunicatum (Becker & Gerd.),Glomus mosseae (Nicol. & Gerd.). Gerd. and Trappe andGigaspora rosea (Nicol & Schenck) in a silty-clay loam soil placed in petri plates. Application of fungicides at 20 mg active ingredient (a.i) kg^–1 soil inhibited spore germination by all three AM-fungal isolates incubated on unsterilized soil for 2 weeks. However, fungicides applied at 10 mg a.i. kg^–1 soil had variable effects on AM-fungal isolates. Fungicide effects on germination and hyphal growth of G.etunicatum were modified by soil pasteurization and CO₂ concentration in petri plates and also by placing spores below the soil surface followed by fungicide drenches. Effects of fungicides on mycorrhiza formation and sporulation of AM fungi, and the resulting host-plant response, were evaluated in the same soil in associated pea (Pisum sativum L.) plants. Fungicides applied at 20 mg a.i. kg^–1 soil did not affect the root length colonized byG. etunicatum, but both benomyl and PCNB reduced sporulation by this fungus. Benomyl and PCNB reduced the root length colonized byG. rosea at 48 and 82 days after transplanting. PCNB also reducedG. mosseae-colonized root length at 48 and 82 days, but benomyl only affected root length colonized byG. mosseae at the earlier time point. Only PCNB reduced sporulation byG. mosseae, consistent with its effect on root length colonized by this fungus. captan reduced the root length colonized by G. rosea at 48 days, but not at 82 days, and reduced colonization byG. mosseae at 82 days, but not at 48 days. Captan did not affect sporulation by any of the fungi.G. rosea spore production was highly variable, but benomyl appeared to reduce sporulation by this fungus. Overall,G. etunicatum was the most tolerant to fungicides in association with pea plants in this soil, andG. rosea the most sensitive. Benomyl and PCNB were overall more toxic to these fungi than captan. Interactions of AM fungi and fungicides were highly variable and biological responses depended on fungus-fungicide combinations and on environmental conditions.     

Mycorrhizae, biocides, and biocontrol 3. Effects of three different fungicides on developmental stages of three AM fungi

The effects of biocide use on nontarget organisms, such as arbuscular mycorrhizal (AM) fungi, are of interest to agriculture, since inhibition of beneficial organisms may counteract benefits derived from pest and disease control. Benomyl, pentachloronitrobenzene (PCNB) and captan were tested for their effects on the germination and early hyphal growth of the AM fungiGlomus etunicatum (Becker & Gerd.),Glomus mosseae (Nicol. & Gerd.). Gerd. and Trappe andGigaspora rosea (Nicol & Schenck) in a silty-clay loam soil placed in petri plates. Application of fungicides at 20 mg active ingredient (a.i) kg^?1 soil inhibited spore germination by all three AM-fungal isolates incubated on unsterilized soil for 2 weeks. However, fungicides applied at 10 mg a.i. kg^?1 soil had variable effects on AM-fungal isolates. Fungicide effects on germination and hyphal growth of G.etunicatum were modified by soil pasteurization and CO₂ concentration in petri plates and also by placing spores below the soil surface followed by fungicide drenches. Effects of fungicides on mycorrhiza formation and sporulation of AM fungi, and the resulting host-plant response, were evaluated in the same soil in associated pea (Pisum sativum L.) plants. Fungicides applied at 20 mg a.i. kg^?1 soil did not affect the root length colonized byG. etunicatum, but both benomyl and PCNB reduced sporulation by this fungus. Benomyl and PCNB reduced the root length colonized byG. rosea at 48 and 82 days after transplanting. PCNB also reducedG. mosseae-colonized root length at 48 and 82 days, but benomyl only affected root length colonized byG. mosseae at the earlier time point. Only PCNB reduced sporulation byG. mosseae, consistent with its effect on root length colonized by this fungus. captan reduced the root length colonized by G. rosea at 48 days, but not at 82 days, and reduced colonization byG. mosseae at 82 days, but not at 48 days. Captan did not affect sporulation by any of the fungi.G. rosea spore production was highly variable, but benomyl appeared to reduce sporulation by this fungus. Overall,G. etunicatum was the most tolerant to fungicides in association with pea plants in this soil, andG. rosea the most sensitive. Benomyl and PCNB were overall more toxic to these fungi than captan. Interactions of AM fungi and fungicides were highly variable and biological responses depended on fungus-fungicide combinations and on environmental conditions.     

Mycorrhizal fungi effects on nutrient composition and yield of soybean seeds

Nutrient composition and yield of soybean [Glycine max (L.) Merr] seeds are heritable traits affected by environmental factors. This study determined the effects of arbuscular‐mycorrhizal (AM) fungi on seed protein, lipid, and phosphorus (P) composition and yield in soybean grown under a high nitrogen (N) regime. Plants were grown in pot cultures without AM fungi in P‐fertilized (+P) or unfertilized (‐P) soil, or in ‐P soil inoculated with one of the AM fungi Glomus mosseae (Nicol. & Gerd.) Gerd, and Trappe (Gm), Glomus etunicatum Becker and Gerd.(Ge), or Gigaspora rosea Nicol. and Schenck (Gr). Seed yields of+AM plants, as a group, were halfway between those of the +P and ‐P plants. Seed size was highest in Gm plants. Differences in protein concentrations between Ge and Gr and the other treatments were highly significant. Seed P and protein concentrations were not significantly correlated (p=0.162), but a highly significant (r =‐0.949) negative correlation between seed P and lipid concentrations was observed. Phosphorus concentration was highest and that of lipids lowest in +AM plants. Seed yield and nutrient composition were independent of the intensity of root colonization. The seed protein/lipid ratio was highly correlated with seed P concentration and was significantly higher for +AM plants, as a group, than for both +P and ‐P ‐AM plants. Differences in seed dry weight, size, seed/ stem ratio, P content, and protein concentration among +AM plants showed mycorrhiza‐specific host responses. These responses suggest that AM fungi can modify soybean seed development and chemical composition.     

Influence of Three Arbuscular Mycorrhizal Fungi and Phosphorus on Growth and Nutrient Status of Taro

Abstract

Glasshouse and field experiments were conducted with micropropagated (tissue culture) taro plants and germinated corms to determine the arbuscular mycorrhizal dependency of taro. The micropropagated plants (cultivar Laiyu 3) were transplanted in plastic pots (3‐L) containing a mixture of vermiculite:perlite:peat:sand (2:1:1:1) with 0 or 8000 units of inoculum potential (UIP) of Glomus mosseae (Nicol & Gerd) Gerdemann and Trappe, Glomus versiforme (Karsten) Berch or Gigaspora rosea Nicolson & Schenck. Budded corms were planted in clay pots (8.5‐L) containing sterilized sandy loam mixed with 0 or 12,000 UIP of G. mosseae or G. versiforme, and 0 or 5 g Ca₃(PO₄)₂ were added. In a field experiment, budded corms were placed in paper pots (0.5‐L) with sterilized sandy loam mixed with 0 or 4000 UIP of G. mosseae or G. versiforme and then planted directly in the field. Inoculation with AM fungi significantly increased survival rate and growth of tissue culture taro plants, and the contents of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), copper (Cu), and zinc (Zn), enhanced the formation of corms, numbers of second and third branch corms and corm yield, and enhanced the contents of crude protein, starch, and amino acids in the corms. Phosphorus fertilizer slightly increased plant yield but reduced plant absorption of Cu and Zn and root colonization by the AM fungi. Relative mycorrhizal dependence (RMD) of micropropagated plants was greater than that of corms.     

Effects of ammonium and nitrate on the growth of vesicular-arbuscular mycorrhizalErythrina poeppigiana O.I. Cook seedlings

Erythrina poeppigiana, a woody tropical plant, was inoculated with vesicular-arbuscular mycorrhizal (VAM) fungiGlomus etunicatum Becker and Gerdeman,G. mosseae Nicol. and Gerd. Gerdeman and Trappe, orG. intraradices Schenk and Smith. Growth, N uptake, and nutrition were evaluated in VAM-inoculated plants and controls fertilized with two levels (3 or 6 mM) of either NH _inf4 ^sup+ -N or NO _inf3 ^sup- -N. The response by the mycorrhizal plants to N fertilization, according to N source and/or level differed significantly from that of the control plants. In general, the growth of the mycorrhizal plants was similar to that of the non-mycorrhizal plants when N was provided as NH _inf4 ^sup+ . When the N source was NO _inf3 ^sup- the control plants grew significantly less than the VAM plants. Inoculation with VAM fungi gave yield increases of 255 and 268% forG. etunicatum-colonized plants, 201 and 164% forG. mosseae-colonized plants and 286 and 218% forG. intraradices-colonized plants fertilized with 3 and 6 mM NO _inf3 ^sup- -N, respectively. The increased growth and acquisition of nutrients by plants fertilized with NO _inf3 ^sup- -N and inoculated with VAM shows that VAM mycelium has a capacity for NO _inf3 ^sup- absorption. The results also showed thatE. poeppigiana seedlings preferred NH _inf4 ^sup+ as an N source.G. etunicatum was the most effective endophyte, not only increasing N, P, Ca, Mg, and Zn uptake in the presence of NO _inf3 ^sup- fertilizer but also P and Mg in the presence of NH _inf4 ^sup+ applications. From these results we conclude that VAM symbiosis affects N metabolism inE. poeppigiana plants and that this species can overcome limitations on the use of NO _inf3 ^sup- -N by the mediation of VAM fungi.     

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.     

Plant and soil responses to mycorrhizal fungi and rhizobacteria in nodulated or nitrate-fertilized peas (Pisum sativum L.)

Rhizosphere organisms affect plant development and soil stability. This study was conducted to determine the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus [Glomus mosseae (Nicol. &>; Gerd.) Gerd. and Trappe] and a rhizobacterium (Bacillus sp.) on nitrate-fertilized or nodulated pea (Pisum sativum L.) plants and on the status of water-stable soil aggregates. The plants were grown in pots in a yellow clay-loam soil, and inoculated with the VAM fungus and the rhizobacterium, with one of the two, or with neither. The Bacillus sp. and G. mosseae did not affect shoot dry mass in nodulated plants. Under N fertilization, the VAM fungus enhanced plant growth, while the rhizobacterium inhibited shoot growth, VAM root colonization, and nodule formation, but enhanced the root:shoot and the seed:shoot ratios. The inhibition of shoot growth and of root colonization appeared to be related. The water stability and pH of the VAM soils were higher than those of the non-VAM soils. The rhizobacterium enhanced the water-stable aggregate status in the non-VAM soils only. Under both N-nutrition regimes, the soils had the greatest proportion of the water-stable aggregates when inoculated with both rhizo-organisms and the lowest when colonized by neither. The two rhizo-organisms affected both plants and soil, and these effects were modified by the source of N input through N₂ fixation or fertilization. Received: 5 April 1995     

An AM fungus and a PGPR intensify the adverse effects of salinity on the stability of rhizosphere soil aggregates of Lactuca sativa

A mesocosm experiment was conducted to examine the effect of an arbuscular mycorrhizal (AM) fungus (Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and a plant growth-promoting rhizobacterium (PGPR) (Pseudomonas mendocina Palleroni), alone or in combination, on the structural stability of the rhizosphere soil of Lactuca sativa L. grown under two levels of salinity. The plants inoculated with P. mendocina had significantly greater shoot biomass than the control plants at both salinity levels, whereas the mycorrhizal inoculation was only effective in increasing shoot biomass at the moderate salinity level. The aggregate stability of soils inoculated with the PGPR and/or G. mosseae significantly decreased with increasing saline stress (about 29% lower than those of soils under non-saline conditions). Only the inoculated soils showed higher concentrations of sodium (Na) under severe saline stress. The severe salinity stress decreased the glomalin-related soil protein (GRSP) concentration, but the highest values of GRSP were recorded in the inoculated soils. Our findings suggest that the use of AM fungi and/or a PGPR for alleviating salinity stress in lettuce plants could be limited by their detrimental effect on soil structural stability.     

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.     

Stability of desiccated rhizosphere soil aggregates of mycorrhizal Juniperus oxycedrus grown in a desertified soil amended with a composted organic residue

Adequate soil structural stability favours the establishment and viability of a stable plant cover, protecting the soil against water erosion in desertified Mediterranean environments. We studied the effect of soil drying-rewetting, inoculation with a mixture of three exotic arbuscular mycorrhizal (AM) fungi (Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and addition of a composted organic residue on aggregate stabilisation of the rhizosphere soil of Juniperus oxycedrus. The AM fungi and composted residue produced similar increases in plant growth, independently of the water conditions. Under well-watered conditions, the highest percentages of stable aggregates were recorded in the amended soil, followed by the soil inoculated with AM fungi. Excepting microbial biomass C, the soil drying increased labile C fractions (water soluble C, water soluble and total carbohydrates), whereas the rewetting decreased significantly such C fractions. Desiccation caused a significant increase in aggregate stability of the rhizosphere soil of all plants, particularly in the amended and inoculated plants. In all treatments, the aggregates formed after soil drying were unstable, since, in the rewetting, they disappear, reaching the initial levels before soil drying. Our results suggest that the aggregation mechanisms developed by rhizosphere microbial community of the amended and inoculated plants under water stress can be particularly relevant in desertified soils exposed to long desiccation periods.     

Pre-inoculation with arbuscular mycorrhizal fungi suppresses root knot nematode (<Emphasis Type="Italic">Meloidogyne incognita</Emphasis>) on cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>)

A pot experiment was conducted to evaluate the influence of pre-inoculation of cucumber plants with each of the three arbuscular mycorrhizal (AM) fungi Glomus intraradices, Glomus mosseae, and Glomus versiforme on reproduction of the root knot nematode Meloidogyne incognita. All three AM fungi tested significantly reduced the root galling index, which is the percentage of total roots forming galls. Numbers of galls per root system were significantly reduced only in the G. intraradices + M. incognita treatment. The number of eggs per root system was significantly decreased by AM fungus inoculation, no significant difference among the three AM fungal isolates. AM inoculation substantially decreased the number of females, the number of eggs g⁻¹ root and of the number of eggs per egg mass. The number of egg masses g⁻¹ root was greatly reduced by inoculation with G. mosseae or G. versiforme. By considering plant growth, nutrient uptake, and the suppression of M. incognita together, G. mosseae and G. versiforme were more effective than G. intraradices.     

Rhodotorulic acid enhances root colonization of tomato plants by arbuscular mycorrhizal (AM) fungi due to its stimulatory effect on the pre-symbiotic stages of the AM fungi

Exudates of Rhodotorula mucilaginosa, a yeast commonly found in the rhizosphere, increased hyphal length of the arbuscular mycorrhizal (AM) fungi Gigaspora rosea and Gigaspora margarita. Rhodotorulic acid (RA), a siderophore compound obtained from R. mucilaginosa exudates, increased hyphal length and branching. Thus, the increase in the number of entry points and the higher AM root colonization of tomato plants in the presence of RA can at least partially be explained by the positive effect of RA on the pre-symbiotic stages of the AM fungi.     

Interactive effects of co-inoculation of Bradyrhizobium japonicum strains and mycorrhiza species on soybean growth and nutrient contents in plant

The main objective of this study was to investigate the effects of co-inoculation with different strains of Bradyrhizobium japonicum (i.e. Helinitro, Rizoking, and Nitragin) and arbuscular mycorrhizal fungi (AMF) species (i.e. Glomus fasciculatum, Glomus versiforme, Glomus intraradices, Glomus mosseae, and Glomus etunicatum) on soybean growth, fungal root colonization, and nutrient uptake of nitrogen (N), phosphorus (P), zinc (Zn), iron (Fe), and copper (Cu). Co-inoculation with various AMF species and rhizobia significantly (p<0.01) increased the soybean biomass production as compared to the non-inoculated controls. Furthermore, AMF colonization of roots of soybean plants increased by 79, 70.1, 67, 63, 57.5, and 50.1% in the presence of G. fasciculatum (GF), G. versiforme (GV), G. intraradices (GI), G. mosseae (GM), and G. etunicatum (GE), and Gmix (a mixed culture of fungi), respectively. Higher nutrient contents were observed in plants co-inoculated with Helinitro and GF. More insight into these results will enable optimization of the effective use of AM fungi in combination with their bacterial partners as a tool for increasing soybean yields in Iran; however, its general analytical framework could be applied to other parts of the world.     

Uptake of Arsenic by Maize Inoculated with Three Different Arbuscular Mycorrhizal Fungi

Effects of inoculation with three different arbuscular mycorrhizal (AM) fungi (Glomus etunicatum, Glomus constrictum, and Glomus mosseae) on arsenic (As) accumulation by maize were investigated by using soil spiked with As at rates of 0, 25, 50, and 100 mg kg^?1. The root colonization rates by the three fungi were significantly different (G. mosseae > G. etunicatum > G. constrictum) and decreased markedly with increasing As concentration in the soil. Inoculation with G. etunicatum or G. mosseae increased maize biomass and phosphorus (P) accumulation (G. mosseae > G. etunicatum) and reduced As accumulation in shoots (G. mosseae ≈ G. etunicatum), whereas inoculation with G. constrictum had little effect on these parameters. Inoculation with G. mosseae produced greater biomass and P uptake and less shoot As accumulation, and therefore it may be a promising approach to reduce As translocation from contaminated soils to plants.     

Effect of Azospirillum inoculants on arbuscular mycorrhiza establishment in wheat and maize plants

Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with Glomus mosseae and Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM Azospirillum phytostimulators does not alter mycorrhization.     

EXPLOITATION OF PHOSPHORUS PATCHES WITH DIFFERENT PHOSPHORUS ENRICHMENT BY THREE ARBUSCULAR MYCORRHIZAL FUNGI

The effect of three arbuscular mycorrhizal (AM) fungi on phosphorus (P) nutrient activation and acquisition by maize from spatially heterogeneous sand was investigated using dual-mesh packages enriched with different P concentrations and compared with non-mycorrhizal cotrols. As would be expected the AM fungi significantly enhanced leaf photosynthetic rate and the biomass and P concentrations in shoots and roots. All three fungi (Glomus intraradices, Glomus mosseae and Glomus etunicatum) displayed the capacity to dissolve inorganic P and promoted P nutrient availability in the packages (P patches). G. etunicatum showed the largest effect comparing with Glomus intraradices and Glomus mosseae, particularly in packages with high concentrations of P. Possible mechanisms involved include the acidification of the P patches by the AM fungi, promotion of the dissolution of the P, and more marked effects of the three fungal isolates with increasing enrichment of P in the patches. Inoculation with G. etunicatum resulted in greater acidification compared to the other two fungi. We conclude that AM fungi can promote P availability by acidifying the soil and consequently exploiting the P in nutrient patches and by facilitating the growth and development of the host plants.     

Influence of AM fungi,inorganic phosphorus and irrigation regimes on plant water relations and soil physical properties in okra (Abelmoschus esculentus L.) – pea (Pisum sativum L.) cropping system in Himalayan acid alfisol

Present investigation studied plant water relations and soil physical properties through AM fungi (Glomus mosseae) to mitigate drought stress in Himalayan acid Alfisol having low water retentivity. Experimentation was carried out at Palampur, India during 2009–2011 in okra–pea cropping system in randomized block design (RBD) replicated thrice with 14 treatments comprising arbuscular mycorrhizal (AM) fungi, varying phosphorus nutrition and irrigation regimes at 40 and 80% available water holding capacity. Integrated use of AM fungi at varying phosphorus (P) levels and irrigation regimes led to significantly higher relative leaf water content (3% each) in okra and pea besides significantly higher xylem water potential (27%) in pea over non-AM fungi counterparts. AM fungi enhanced water-use-efficiency in okra (5–17%) and pea (12–35%) over non–AM fungi counterparts. AM fungi also improved water holding capacity (5–6%) and mean weight diameter of soil particles (4–9%) over non–AM fungi counterparts; but, had nominal or no effect on bulk density. Mycorrhizal plants maintained higher tissue water content imparting greater drought resistance to plants over non–mycorrhizal plants at moisture stress. It is inferred that integrated application of AM fungi and P at varying irrigation regimes improved the plant water relations vis-à-vis drought resistance, crop productivity, WUE, soil aggregation and water holding capacity in okra–pea sequence in Himalayan acid Alfisol.     

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.     

Responses of Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil

Responses of three multipurpose fruit tree species, Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam., to inoculation with five species of arbuscular mycorrhizal fungi, Acaulospora spinosa Walker and Trappe, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, Glomus intraradices Schenck and Smith, Glomus aggregatum Schenck and Smith emend. Koske and Glomus manihotis Howeler, Sieverding and Schenck, differed markedly with respect to functional compatibility. This was measured as root colonization, mycorrhizal dependence (MD) and phosphorus concentrations in shoots of plants. Root colonization of fruit trees by A. spinosa, G. aggregatum and G. manihotis was high and tree growth increased significantly as a consequence. G. intraradices also colonized well, but provided little growth benefit. G. mosseae colonized poorly and did not stimulate plant growth. The MD of P. biglobosa and T. indica was similar, reaching no more than 36%, while Z. mauritiana showed the highest MD values, reaching a maximum of 78%. The Z. mauritiana A. spinosa combination was the most responsive with respect to total biomass production; phosphorus (P) absorption probably contributed to this more than the absorption of sodium, potassium, magnesium or calcium. The density and length of root hairs were positively correlated with MD, suggesting that root hairs are not indicative of MD. Received: 20 January 1997     

Screening of Arbuscular Mycorrhizal Fungi for Symbiotic Efficiency with Sweet Potato

A greenhouse study was conducted to study the efficiency of 14 isolates of arbuscular mycorrhizal (AM) fungi isolated from a local agricultural soil on the productivity of sweet potato (Ipomoea batatas). The different AM fungi enhanced the biomass and nutritional status of sweet potato seedlings to different extents. The genus Glomus was more effective than Acaulospora or Scutellospora. Efficiency also varied among isolates of Glomus irrespective of individual host plant or location of origin. Intraspecific differences were sometimes greater than interspecific differences. Benefits deriving from fungal isolates were positively correlated with the root-colonization rate and the abundance of extraradical propagules of the AM fungi. Taking plant yield parameters, nutritional status of the plants, and fungal attributes into consideration, GEGM (Glomus etunicatum together with Glomus mosseae) and GE6 (Glomus etunicatum) were the most effective AM symbionts for sweet potato under the experimental conditions.