An assessment of the usefulness of solution culture in screening for phosphorus efficiency in wheat

This study provides an assessment of the suitability of solution culture for screening plants for phosphorus (P) efficiency. Two varieties of wheat (Triticum aestivum L.), Brookton and Krichauff, were compared. In a low-phosphorus soil Brookton was found to be more P-efficient than Krichauff, accumulating 32% more P with a similar dry weight. However, when the two cultivars were grown in solution culture this difference was no longer evident and in some cases was reversed. High-affinity phosphate transport characteristics of the roots were also similar for Brookton and Krichauff and there were no differences between the two cultivars in P deficiency-induced root exudates (acid phosphatase or organic acids). The only notable difference between the two varieties when grown in solution culture related to morphological features of the root system. Although similar root weights and root surface areas were observed for both cultivars, Brookton had a 37–39% higher maximum root length. In other words, Brookton grew fewer but longer roots, with fewer laterals than Krichauff. This morphology may be advantageous in soil environments where there is nutrient heterogeneity since it would permit a large volume of soil to be explored with minimal expense of energy, preceding a localised proliferation of lateral roots and root hairs in patches of nutrient-rich soil. Overall, it was found that the growth characteristics of wheat plants in solution culture were not reliable indicators of P efficiency, and that important traits for P efficiency are likely to be linked to efficient exploration of nutritionally heterogeneous soil.     

Effectiveness of arbuscular mycorrhizal fungi in phytoremediation of lead- contaminated soil by vetiver grass

A greenhouse experiment was conducted to evaluate the effectiveness of arbuscular mycorrhizal (AM) fungi in phytoremediation of lead (Pb)-contaminated soil by vetiver grass. Experiment was a factorial arranged in a completely randomized design. Factors included four Pb levels (50, 200, 400, and 800 mg kg^?1) as Pb (NO₃)₂, AM fungi at three levels (non mycorrhizal (NM) control, Rhizophagus intraradices, Glomus versiforme). Shoot and root dry weights (SDW and RDW) decreased as Pb levels increased. Mycorrhizal inoculation increased SDW and RDW compared to NM control. With mycorrhizal inoculation and increasing Pb levels, Pb uptake of shoot and root increased compared to those of NM control. Root colonization increased with mycorrhizal inoculation but decreased as Pb levels increased. Phosphorus concentration and uptake in shoot of plants inoculated with AM fungi was significantly higher than NM control at 200 and 800 mg Pb kg^?1. The Fe concentration, Fe and Mn uptake of shoot in plants inoculated with Rhizophagus intraradices in all levels of Pb were significantly higher than NM control. Mycorrhizal inoculation increased Pb extraction, uptake and translocation efficiencies. Lead translocation factor decreased as Pb levels increased; however inoculation with AM fungi increased Pb translocation.     

Effect of Tilemsi phosphate rock-solubilizing microorganisms on phosphorus uptake and yield of field-grown wheat (Triticum aestivum L.) in Mali

With the broad aim of biologically improving P uptake by wheat fertilized with Tilemsi phosphate rock (TPR), we investigated the effect of inoculation with TPR-solubilizing microorganisms isolated from Malian soils and with a commercial isolate of the arbuscular mycorrhizal (AM) fungus Glomus intraradices (Gi). AM root length colonization, and growth yield and P concentration of the cultivar Tetra of wheat were measured under field conditions in Mali. Experimental plots were established in Koygour (Diré) during the 2001–2002 cropping season. Inoculation treatments included two fungal isolates, Aspergillus awamori (C1) and Penicillium chrysogenum (C13), and an isolate of Pseudomonas sp. (BR2), used alone or in fungus-bacterium combinations in the presence or absence of the AM fungus Gi. In fertilized treatments, 0 or 30 kg P ha⁻¹ was applied as TPR or diammonium phosphate (DAP). In 45-day-old wheat plants, the highest root length AM colonization (62%) was observed with TPR fertilized wheat inoculated with Gi and BR2. Our results suggest that BR2 is a mycorrhizal-helper bacteria and a good plant growth-promoting rhizobacteria. In fact, inoculation of wheat Tetra fertilized with TPR with a combination of Gi, BR2 and C1 produced the best grain yield with the highest P concentration. This work shows that by inoculating seeds with TPR-solubilizing microorganisms and AM fungi under field conditions in Mali it is possible to obtain wheat grain yields comparable to those produced by using the expensive DAP fertilizer.     

Field response of wheat to arbuscular mycorrhizal fungi and drought stress

Mycorrhizal plants often have greater tolerance to drought than nonmycorrhizal plants. This study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat (Triticum aestivum L.) cultivars grown in the field under well-watered and water-stressed conditions. Wheat seeds were planted in furrows after treatment with or without the AM fungi Glomus mosseae or G. etunicatum. Roots were sampled at four growth stages (leaf, tillering, heading and grain-filling) to quantify AM fungi. There was negligible AM fungi colonization during winter months following seeding (leaf sampling in February), when soil temperature was low. During the spring, AM fungi colonization increased gradually. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi isolates than water-stressed plants. Plants inoculated with G. etunicatum generally had higher colonization than plants colonized with G. mosseae under both soil moisture conditions. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. etunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentrations than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.     

Zinc (Zn)-phosphorus (P) Interactions in Two Cultivars of Spring Wheat (Triticum aestivum L.) Differing in P Uptake Efficiency

Zinc-phosphorus (Zn-P) interactions were investigated in twowheat cultivars (Brookton and Krichauff) differing in P uptakeefficiency. The experiment was carried out in a growth chamber.Rock phosphate or CaHPO₄were used as P sources, and ammoniumnitrate or nitrate only as nitrogen sources. Two Zn levels wereused: 0.22 and 2.2 mg ZnSO₄.5H₂O kg^-1. The results confirmedthat Brookton had a higher P uptake efficiency than Krichauffunder low P conditions, irrespective of nitrogen and Zn supply.Zn supply had little effect on tissue P concentration and Puptake per unit of root weight in either cultivar, irrespectiveof nitrogen supply. An increase in P availability caused a significantreduction in Zn uptake per unit of root weight, and tissue concentrationof Zn in both cultivars. The reduction in tissue Zn concentrationcannot be explained entirely by a dilution effect. Zn uptakeby, and Zn concentrations in, Brookton (with high P uptake efficiency)were significantly lower than those of Krichauff. Zn concentrationsin Brookton were more sensitive to P uptake than those in Krichauff.It is suggested that high P uptake efficiency may depress plantuptake of Zn, and therefore cause a reduction in the concentration(density) of Zn in grains of wheats grown in low P (and possiblylow Zn) soils. Copyright 2001 Annals of Botany Company Phosphorus efficiency, translocation, uptake, zinc-phosphorus interaction, wheat     

Plant growth and cation composition of two cultivars of spring wheat (Triticum aestivum L.) differing in P uptake efficiency.

Phosphorus (P)-zinc (Zn) interactions were investigated in two wheat cultivars (Brookton versus Krichauff) differing in P uptake efficiency. The experiment was done in a growth chamber. Rock phosphate (RP) or CaHPO4 (CaP) were used as P sources, and ammonium nitrate (AN) or nitrate only (NO) were used as nitrogen sources. Two Zn levels were used, 0.22 mg x kg(-1) (LZ) and 2.2 mg ZnSO4.7H2O x kg(-1) (HZ), respectively. P availability significantly affected plant biomass production, but Zn supply had little effect. Plants fed ammonium nitrate had significantly lower concentrations of cations than those fed nitrate only. Cultivar Brookton (with higher P uptake efficiency) consistently had lower concentrations of cations than cv. Krichauff (with low P uptake efficiency) under limited P supply. The differences in concentrations of cations increased with the decrease in P availability, but were not affected by Zn supply. The ratio of potassium in roots to shoots of cultivar Brookton was always higher than in cultivar Krichauff. Based on these findings, it is postulated that the lower concentrations of cations in cultivar Brookton are related to root exudation of organic anions, and a conceptual model is established to describe the regulation of root exudation of organic anions and concentrations of cations.     

Response of the grapevine rootstock Richter 110 to inoculation with native and selected arbuscular mycorrhizal fungi and growth performance in a replant vineyard

Two indigenous arbuscular mycorrhizal (AM) fungi from the Mediterranean wine growing area in the Northeast of Spain were isolated and classified as Glomus intraradices Schenck & Smith. Both native fungi were found to increase the growth of the vine rootstock 110 Richter under greenhouse conditions compared with G. intraradices (BEG 72) and a phosphorus (P) fertilization treatment. The effectivity of field inoculation of Cabernet Sauvignon plants grafted on Richter 110 with the former native fungi and with G. intraradices BEG 72 in a replant vineyard severely infested by the root-rot fungus Armillaria mellea (Vahl ex Fr.) Kummer was assessed. The native fungi were not effective at enhancing plant development, and only G. intraradices BEG 72, resulted in a positive response. Field inoculation with this selected fungus increased plant shoot dry weight at the end of the first growing season.     

Seed phosphorus (P) content affects growth,and P uptake of wheat plants and their association with arbuscular mycorrhizal (AM) fungi

Two experiments were carried out in a growth chamber and a naturally lit glasshouse to investigate the influence of seed phosphorus (P) reserves on growth and P uptake by wheat plants (Triticum aestivum cv Krichauff), and their association with arbuscular mycorrhizal (AM) fungi. Increased seed P reserves improved plant growth at a range of P supply up to over 100 mg P kg^–1 soil. Plants grown from seeds with high P reserves tended to accumulate more P from soil, which was mainly attributed to better root system development. Mycorrhizal colonisation did not significantly affect P uptake of plants grown with low irradiance (in growth chamber). However, in the naturally lit glasshouse, mycorrhizal plants had significantly higher P concentrations than non-mycorrhizal plants. Furthermore, mycorrhizal plants grown from seeds low in P accumulated similar amounts of P compared with those grown from seeds with high P, indicating that mycorrhizal colonisation may overcome the disadvantage of having low seed P reserves in the field.     

Beyond the rhizosphere: growth and function of arbuscular mycorrhizal external hyphae in sands of varying pore sizes

Research on nutrient acquisition by symbiotic arbuscular mycorrhizal (AM) fungi has mainly focused on the root–fungus interface and less attention has been given to the growth and functioning of external hyphae in the bulk soil. The growth and function of external hyphae may be affected by unfavourable soil environments, such as compacted soils in which pores may be narrow. The effects of pore size on the growth of two AM fungi (Glomus intraradices and G. mosseae) and their ability to transport ³³P from the bulk soil to the host were investigated. Trifolium subterraneum L. plants were grown individually in `single arm cross-pots' with and without AM fungi. The side arm was separated from the main compartment by nylon mesh to prevent root penetration. It contained three zones: 5 mm of soil:sand mix (HC1); 25 mm of media treatment (HC2); and 20 mm of ³³P-labelled soil (HC3). There were four media treatments; soil and three types of quartz sand with most common continuous pore diameters of 100, 38 and 26 m. AM plants had similar growth and total P uptake in all treatments. However, plants grown with G. intraradices contained almost three times more ³³P than those grown with G. mosseae, indicating G. intraradices obtained a greater proportion of P at a distance from the host roots. Differences in P acquisition were not correlated with production of external hyphae in the four media zones and changes in sand pore size did not affect the ability of the fungi studied to acquire P at a distance from the host roots. Production of external hyphae in HC2 was influenced by fungal species and media treatment. Both fungi produced maximum amounts of external hyphae in the soil medium. Sand pore size affected growth of G. intraradices (but not G. mosseae) and hyphal diameter distributions of both fungi. The results suggest that not only are G. mosseae and G. intraradices functionally complementary in terms of spatial phosphorus acquisition, they are also capable of altering their morphology in response to the soil environment.     

Response of Arbuscular Mycorrhizal Fungi on Wheat (Triticum aestivum L.) Grown Conventionally and on Beds in a Sandy Loam Soil

The present study was undertaken to assess the benefit and compare the functioning of AM fungi on wheat grown conventionally and on beds. Ten treatment combinations were used, treatments 1 and 2: no fertilizers with and without arbuscular mycorrhizal (AM) fungi (In vitro produced Glomus intraradices); 3:100% of recommended NPK: (120 kg ha⁻¹ N; 60 kg ha⁻¹ P; 50 kg ha⁻¹ K), and 4 and 5: 75% of recommended NPK dose with and without AM inoculation in a 5 × 2 split-plot design on wheat using conventional/flat system and elevated/raised bed system. The maximum grain yield (3.84 t ha⁻¹) was obtained in AM fungi inoculated plots of raised bed system applied with 75% NPK and was found higher (although non- significant) than the conventional (3.73 t ha⁻¹) system. The AM inoculation at 75% fertilizer application can save 8.47, 5.38 kg P and 16.95, 10.75 kg N ha⁻¹, respectively, in bed and conventional system. While comparing the yield response with 100% fertilizer application alone, AM inoculation was found to save 20.30, 15.79 kg P and 40.60, 31.59 kg N ha⁻¹, respectively, in beds and conventional system. Mycorrhizal inoculation at 75% NPK application particularly in raised bed system seems to be more efficient in saving fertilizer inputs and utilizing P for producing higher yield and growth unlike non-mycorrhizal plants of 100% P. Besides the yield, mycorrhizal plants grown on beds had higher AM root colonization, soil dehydrogenases activity, and P-uptake. The present study indicates that the inoculation of AM fungi to wheat under raised beds is better response (although non-significantly higher) to conventional system and could be adopted for achieving higher yield of wheat at reduced fertilizer inputs after field validation.     

Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

 A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production. Accepted: 15 July 1998     

Phosphorus uptake by a community of arbuscular mycorrhizal fungi in jarrah forest

Communities of indigenous arbusuclar mycorrhizal (AM) fungi are expected to alter phosphorus uptake and biomass productivity of plants according to characteristics of the life cycles of the fungi present and the way they interact with each other inside roots and with host plants. Differences in the relative abundance of AM fungi inside roots could influence P uptake if the fungi present differ in effectiveness at accessing P and transferring it to the plant. However, it is difficult to assess the contribution of AM fungi under field conditions. We investigated P uptake, from point sources of P placed 2, 4 and 6 cm from roots, by plants colonised by a community of AM fungi in jarrah forest soil. Roots were retained within a mesh bag to prevent them from growing towards the point source of P. The relative abundance of morphotypes of fungi inside roots and the P status of plants were assessed after 12 and 16 weeks. First, a bioassay was carried out in undisturbed forest soil cores using two host plants, a forest understorey plant Phyllanthus calycinus Labill and the annual pasture species subterranean clover (Trifolium subterraneaumL.), to assess the infectivity of the indigenous community of AM fungi. Roots of both bioassay host plants were colonised in similar proportions by morphotypes of AM fungi resembling Glomus, Acaulospora, Scutellospora and fine endophytes. In this bioassay, there were positive correlations between the proportion of root length colonised and plant biomass and P uptake for P. calycinus, but not for subterranean clover. In the experiment assessing the capacity of P. calycinus to access P placed at increasing distances from the root, shoot P content and concentration in P. calycinus were greater when P was placed 2 cm compared with 4 and 6 cm from roots. The length of hyphae in the vicinity of the point source of P decreased with increasing distance from the plant. The extent to which the individual AM fungi were involved in P uptake is not known. The Glomus morphotype was dominant at both times of sampling.     

Effects of preplant inoculation of apple (Malus domestica Borkh.) with arbuscular mycorrhizal fungi on population growth of the root-lesion nematode,Pratylenchus penetrans

Six species of arbuscular mycorrhizal (AM) fungi (Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. mosseae and G. versiforme) were evaluated, in three greenhouse experiments, for their effects on reproduction of the root-lesion nematode, Pratylenchus penetrans, and growth of Ottawa 3 apple rootstock. Glomus mosseae increased total dry weights of nematode-inoculated and non-inoculated rootstock in all three greenhouse experiments, and G. intraradices increased dry weights in two of three greenhouse experiments. Plants inoculated with G. mosseae generally supported fewer P. penetrans per gram of root than plants inoculated with other AM fungi, but did not differ significantly from the controls in any greenhouse experiment. Colonization of roots by AM fungi was reduced by P. penetrans at initial inoculum densities greater than 250 nematodes/L soil. In field trials, preplant inoculation with either G. intraradices or G. mosseae increased rootstock growth and leaf concentrations of P, Mg, Zn and Cu in fumigated plots but not in non-fumigated plots, indicating that colonization by native AM fungi in non-fumigated plots may have been sufficient for adequate nutrient acquisition. The abundance of vesicles and arbuscules was greater in roots of plants inoculated with AM fungi before planting than in roots of non-inoculated plants, in both fumigated and non-fumigated plots. P. penetrans per gram of root and per 50 ml soil were significantly lower for G. mosseae- inoculated plants than for non-inoculated plants in fumigated soil but not in non-fumigated soil.     

Indigenous and introduced arbuscular mycorrhizal fungi contribute to plant growth in two agricultural soils from south-western Australia

Arbuscular mycorrhizal (AM) fungi occur in all agricultural soils but it is not easy to assess the contribution they make to plant growth under field conditions. Several approaches have been used to investigate this, including the comparison of plant growth in the presence or absence of naturally occurring AM fungi following soil fumigation or application of fungicides. However, treatments such as these may change soil characteristics other than factors directly involving AM fungi and lead to difficulties in identifying the reason for changes in plant growth. In a glasshouse experiment, we assessed the contribution of indigenous AM fungi to growth of subterranean clover in undisturbed cores of soil from two agricultural field sites (a cropped agricultural field at South Carrabin and a low input pasture at Westdale). We used the approach of estimating the benefit of AM fungi by comparing the curvature coefficients ( C) of the Mitscherlich equation for subterranean clover grown in untreated field soil, in field soil into which inoculum of Glomus invermaium was added and in soil fumigated with methyl bromide. It was only possible to estimate the benefit of mycorrhizas using this approach for one soil (Westdale) because it was the only soil for which a Mitscherlich response to the application of a range of P levels was obtained. The mycorrhizal benefit ( C of mycorrhizal vs. non-mycorrhizal plants or C of inoculated vs. uninoculated plants) of the indigenous fungi corresponded with a requirement for phosphate by plants that were colonised by AM fungi already present in the soil equivalent to half that required by non-mycorrhizal plants. This benefit was independent of the plant-available P in the soil. There was no additional benefit of inoculation on plant growth other than that due to increased P uptake. Indigenous AM fungi were present in both soils and colonised a high proportion of roots in both soils. There was a higher diversity of morphotypes of mycorrhizal fungi in roots of plants grown in the Westdale soil than in the South Carrabin soil that had a history of high phosphate fertilizer use in the field. Inoculation with G. invermaium did not increase the level of colonisation of roots by mycorrhizal fungi in either soil, but it replaced approximately 20% of the root length colonised by the indigenous fungi in Westdale soil at all levels of applied P. The proportion of colonised root length replaced by G. invermaium in South Carrabin soil varied with the level of application of P to the soil; it was higher at intermediate levels of recently added soil P.     

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs. Electronic Supplementary Material Supplementary material is available for this article at     

Assessment of arbuscular mycorrhizal fungi diversity in the rhizosphere of <Emphasis Type="Italic">Viola calaminaria</Emphasis> and effect of these fungi on heavy metal uptake by clover

 The ability of arbuscular mycorrhizal (AM) fungi from a metal-tolerant plant (Viola calaminaria, violet) to colonise and reduce metal uptake by a non-tolerant plant (Trifolium subterraneum, subterranean clover) in comparison to a metal-tolerant AM fungus isolated from a non-tolerant plant was studied. AM spores from the violet rhizosphere and from violet roots were characterised by polymerase chain reaction (PCR) amplification of the SSU rDNA, and sequencing. Subterranean clover was grown in pots containing a soil supplemented with Cd and Zn salts and inoculated either with a mixture of spores extracted from the violet rhizosphere or with spores of a Cd-tolerant Glomus mosseae P2 (BEG 69), or non-inoculated. The diversity of fungi, including AM fungi, colonising clover roots was assessed and analysed using terminal-restriction fragment length polymorphism. At least four different Glomus species were found in the violet rhizosphere. After 8 weeks in a growth chamber, colonisation of clover roots with spores from the violet rhizosphere increased Cd and Zn concentrations in clover roots without significantly affecting the concentrations of metals in the shoot and plant growth. G. mosseae P2 reduced plant growth and slightly increased the Cd concentration. Only one AM fungus (Glomus b) from the violet rhizosphere colonised clover roots, but other fungi were present. AM fungi from heavy metal-contaminated soils and associated with metal-tolerant plants may be effective in accumulating heavy metals in roots in a non-toxic form. Accepted: 7 July 2000     

Seasonal variation of arbuscular mycorrhizal fungi in temperate grasslands along a wide hydrologic gradient

We studied seasonal variation in population attributes of arbuscular mycorrhizal (AM) fungi over 2 years in four sites of temperate grasslands of the Argentinean Flooding Pampas. The sites represent a wide range of soil conditions, hydrologic gradients, and floristic composition. Lotus glaber, a perennial herbaceous legume naturalised in the Flooding Pampas, was dominant at the four plant community sites. Its roots were highly colonised by AM fungi. Temporal variations in spore density, spore type, AM root colonisation, floristic composition and soil chemical characteristics occurred in each site and were different among sites. The duration of flooding had no effect on spore density but depressed AM root colonisation. Eleven different types of spores were recognized and four were identified. Two species dominated at the four sites: Glomus fasciculatum and Glomus intraradices. Spore density was highest in summer (dry season) and lowest in winter (wet season) with intermediate values in autumn and spring. Colonisation of L. glaber roots was highest in summer or spring and lowest in winter or autumn. The relative density of G. fasciculatum and G. intraradices versus Glomus sp. and Acaulospora sp. had distinctive seasonal peaks. These seasonal peaks occurred at all four sites, suggesting differences among AM fungus species with respect to the seasonality of sporulation. Spore density and AM root colonisation when measured at any one time were poorly related to each other. However, spore density was significantly correlated with root colonisation 3 months before, suggesting that high colonisation in one season precedes high sporulation in the next season.     

Contribution of <Emphasis Type="Italic">Glomus intraradices</Emphasis> inoculation to nutrient acquisition and mitigation of ionic imbalance in NaCl-stressed <Emphasis Type="Italic">Trigonella foenum-graecum</Emphasis>

The study aimed to investigate the effects of an AM fungus (Glomus intraradices Schenck and Smith) on mineral acquisition in fenugreek (Trigonella foenum-graecum) plants under different levels of salinity. Mycorrhizal (M) and non-mycorrhizal (NM) fenugreek plants were subjected to four levels of NaCl salinity (0, 50, 100, and 200 mM NaCl). Plant tissues were analyzed for different mineral nutrients. Leaf senescence (chlorophyll concentration and membrane permeability) and lipid peroxidation were also assessed. Under salt stress, M plants showed better growth, lower leaf senescence, and decreased lipid peroxidation as compared to NM plants. Salt stress adversely affected root nodulation and uptake of NPK. This effect was attenuated in mycorrhizal plants. Presence of the AM fungus prevented excess uptake of Na⁺ with increase in NaCl in the soil. It also imparted a regulatory effect on the translocation of Na⁺ ions to shoots thereby maintaining lower Na⁺ shoot:root ratios as compared to NM plants. Mycorrhizal colonization helped the host plant to overcome Na⁺-induced Ca²⁺ and K⁺ deficiencies. M plants maintained favorable K⁺:Na⁺, Ca²⁺:Na⁺, and Ca²⁺:Mg²⁺ ratios in their tissues. Concentrations of Cu, Fe, and Zn²⁺ decreased with increase in intensity of salinity stress. However, at each NaCl level, M plants had higher concentration of Cu, Fe, Mn²⁺, and Zn²⁺ as compared to NM plants. M plants showed reduced electrolyte leakage in leaves as compared to NM plants. The study suggests that AM fungi contribute to alleviation of salt stress by mitigation of NaCl-induced ionic imbalance thus maintaining a favorable nutrient profile and integrity of the plasma membrane.     

Phosphorus (P) efficiencies and mycorrhizal responsiveness of old and modern wheat cultivars

A pot experiment was carried out in a growth chamber to investigate P efficiencies and mycorrhizal responsiveness of modern (Krichauff and Excalibur) and old (Khapstein, Bobin, Comeback and Purple Straw) wheat cultivars (Triticum aestivum). The arbuscular mycorrhizal fungus (AMF) used in this study was Glomus intraradices. The growth medium was a soil/sand mixture with NaHCO₃-extractable P of 9.4 mg P kg^–1 and no extra P was added. Plant P efficiencies (uptake, utilisation and agronomic) were found to differ significantly between cultivars, but no general trends of changes with the year of release of the cultivar were found. AMF colonisation was found to decrease plant growth under our experimental conditions with low light intensity. Mycorrhizal responsiveness (MR) was measured in terms of the improvement in plant P nutrition (shoot P concentrations). MR was found to be generally lower in modern cultivars than in old cultivars, indicating that modern breeding programs may have reduced the responsiveness of modern wheat cultivars to arbuscular mycorrhizal fungi. MR was also found to decrease in general with increased plant P utilisation efficiency.     

Interactive effects of temperature and arbuscular mycorrhizal fungi on growth,P uptake and root respiration of<Emphasis Type="Italic"> Capsicum annuum</Emphasis> L.

Capsicum annuum (pepper) plants were inoculated with the arbuscular mycorrhizal (AM) fungi Glomus intraradices Smith and Schenck, an undescribed Glomus sp. (AZ 112) or a mixture of these isolates. Control plants were non-mycorrhizal. Plants were grown for 8 weeks at moderate (20.7–25.4°C) or high (32.1–38°C) temperatures. Colonization of pepper roots by G. intraradices or the Glomus isolate mixture was lower at high than at moderate temperatures, but colonization by Glomus AZ112 was somewhat increased at high temperatures. Pepper shoot and root dry weights and leaf P levels were affected by an interaction between temperature and AM fungal treatments. At moderate temperatures, shoot dry weights of plants colonized by the Glomus isolate mixture or non-AM plants were highest, while root dry weights were highest for non-AM plants. At high temperatures, plants colonized by Glomus AZ112 or the non-AM plants had the lowest shoot and root dry weights. AM plants had generally higher leaf P levels at moderate temperatures and lower P levels at high temperatures than non-AM plants. AM plants also had generally higher specific soil respiration than non-AM plants regardless of temperature treatment. At moderate temperatures, P uptake by all AM plants was enhanced relative to non-AM plants but there was no corresponding enhancement of growth, possibly because less carbon was invested in root growth or root respiratory costs increased. At high temperatures, pepper growth with the G. intraradices isolate and the Glomus isolate mixture was enhanced relative to non-AM controls, despite reduced levels of AM colonization and, therefore, apparently less fungal P transfer to the plant.