Response of two species of cassia and Gliricidia sepium to vesicular‐arbuscular mycorrhizal infection

Abstract

A pot experiment was conducted to evaluate the response to vesicular‐arbuscular mycorrhizal (VAM) infection of two species of Cassia and Gliricidia sepium in an oxisol with two levels of soil P. At P level optimum for VAM activity, comparable levels of VAM infection were observed on the roots of the test species. However, the species reacted differently to VAM infection. Hence, VAM inoculation significantly stimulated dry matter accumulation in C. spectabilis and G. sepium, but had no positive influence on this variable in C. reticulata. These differences were not explainable in terms of tissue P status, because P uptake was significantly enhanced by inoculation in all the species tested. At the higher soil P level, roots of all species were colonized by the inoculum, but colonization level in C. reticulata and G. sepium was reduced. Nevertheless, only C. spectabilis benefitted from the presence VAM endophytes at this level of soil P. The results underline the significance of ascertaining the mycorrhizal requirements of host species before reliable VAM inoculation recommendation could be made.     

Boron fertilization,vesicular‐arbuscular mycorrhizal colonization and growth of citrus jambhiri lush

The role of boron (B) fertilization in the vesicular‐arbuscular mycorrhizal (VAM) colonization and growth of container‐grown Citrus seedlings was evaluated. Citrus jambhiri Lush, seedlings inoculated with Glomus fasciculatum, Glomus etunicatum or non‐inoculated were grown in a sandy loam soil for sixteen weeks. Seedlings were fertilized with 25 ug/ml B applied to the foliage as a mist, to the soil as a solution, or to both the foliage and the soil. Boron applied to the foliage or to the soil significantly increased root exudation of reducing sugars and amino acids two weeks after seedling germination. Subsequently, foliar fertilization with B significantly increased VAH colonization of seedlings relative to the controls. Plants inoculated with G. fasciculatum were larger and had greater VAM development than those inoculated with G. etunicatum. The growth of the noninoculated seedlings was not enhanced by B fertilization. The superior VAH colonization and growth of inoculated seedlings fertilized with B suggests that B stimulates the efficacy of plant fungi symbiosis.     

The sensitivity of three vesicular‐arbuscular mycorrhizal species to simulated erosion

Abstract

A greenhouse experiment was conducted to determine the effectiveness of three vesicular‐arbuscular mycorrhizal (VAM) species in an Oxisol subjected to simulated erosion using Leucaena leucocephala as an indicator host. The extent of colonization of leucaena roots increased significantly due to VAM inoculation of the eroded and uneroded soils. The highest level of VAM colonization was observed when leucaena was grown in association with Glomus aggregatum. followed by G. mosseae and G. etunicatum. Increased infection associated with inoculation of the eroded soil did not result in enhanced mycorrhizal effectiveness. Inoculation of the uneroded soil, however, led to significant improvement in root colonization as well as in symbiotic effectiveness. Suppression in expression of mycorrhizal effectiveness in the eroded soil appears to be a result of nutrient deficiency. The results suggest the importance of restoring lost nutrients before differences in VAM species could be effectively exploited for a successful establishment of a mycorrhizal plants in eroded soils.     

Genotypic variation in vesicular‐arbuscular mycorrhizal dependence of the pejibaye palm

Two experiments were undertaken to determine the degree of mycorrhizal dependency of pejibaye (Bactris gasipaes, Palmae) seedling progenies from two Amazonian (Pampa Hermosa; Putumayo) and one Central American (Guatuso) land races. Plants were grown in subsurface samples of either an Oxisol (the Amazonian progenies) or an Ultisol, with or without inoculation with the vesicular‐arbuscular mycorrhizae fungus (VAMF) Glomus aggregatum, at three concentrations of soil solution phosphorous (P). VAMF inoculation enhanced leaf phosphorus (P) concentration and dry matter accumulation at the intermediate soil P concentration in all progenies. Dry matter accumulation was enhanced by 17%, 54%, and 64% in the Pampa Hermosa, Putumayo, and Guatuso progenies, respectively. They are therefore classified as being marginally (Pampa Hermosa) or highly dependent. This infra‐specific genetic variation with respect to mycorrhizal dependency merits further study for possible exploitation in plant improvement for sustainable agriculture.     

Establishment of soil solution P levels for studies involving vesicular‐arbuscular mycorrhizal symbiosis

Abstract

A phosphorus sorption curve was developed to evaluate the influence of established levels of soil solution P on the development of vesicular‐arbuscular mycorrhizal (VAM) activity in Leucaena leucocephala (Lam.) de Wit grown on soil:sand mixture. The P sorption curve developed after nutrient amendment and wetting and drying treatments in the greenhouse predicted levels of P established in the soil solution more accurately than P sorption isotherm developed in the laboratory.

VAM activity measured in terms of P content of pinnules of Leucaena was significantly higher at lower soil solution P levels (0.01 and 0.02 mg/L) than at higher levels. In general, VAM activity declined after reaching a peak value at 30 days after planting (DAP).

Soil solution P levels monitored during the course of the experiment indicated that low initial P levels (0.01 and 0.02 mg/L) were readily maintained than higher ones. The proposed approach is thus appropriate for establishing soil solution P levels that permit optimal VAM activity.     

Relative effectiveness of phosphorus on narrow‐leaf and broadleaf birdsfoot trefoil growth and the effect of added phosphorus on vesicular arbuscular mycorrhizal infection

The relative effectiveness of phosphorus (P) applications on growth and the effect of added P on the extent of infection of roots of narrowleaf birsfoot trefoil (Lotus tenuis) and of broadleaf birdsfoot trefoil (Lotus corniculatus) by an indigenous VAM fungi (Glomus sp.) was studied on a P‐deficient soil (Typic Natraquoll). In terms of rate of increase of shoot growth per unit of added P, broadleaf was more efficient than narrowleaf birsdfoot trefoil but they did not differ in the relative effectiveness of P for growth. For the two Lotus species, when increasing the level of added P there was an initial increase in the percentage of root length infected, and then with further additions, there was a consistent decrease of the infection. For narrowleaf, the maximum percentage of root length infected was when plants reached 11% of their maximum shoot growth. Whereas for broafleaf, the maximum percentage of root infected was when plants reached the 66% of their maximum shoot growth. Despite differences in both, the shape of the response curve of shoot growth to P and the extent of infection between Lotus species, they did not differ in their ability to utilize the P that had reacted with the soil for a period of time.     

Effects of benomyl on vesicular‐arbuscular mycorrhizal infection of red clover (Trifolium pratense L.) and consequences for phosphorus inflow.

The roots of red clover plants inoculated with the vesicular‐arbuscular mycorrhizal fungus Glomus clarus Nicolson & Schenck were treated with a drench of benomyl at a time when mycorrhizal infection was already well established. Benomyl halted further infection and reduced phosphorus inflow by one order of magnitude compared to untreated controls. The fungicide also decreased the rate of plant growth probably as a consequence of reduced phosphorus inflow.     

Effect of three vesicular‐arbuscular mycorrhizae species and phosphorus on reproductive and vegetative growth of three strawberry cultivars 1

A study was undertaken to evaluate the yield, fruit size, and vegetative growth of three strawberry cultivars inoculated with three vesicular‐arbuscular mycorrhizal (VAM) species at three phosphorus (P) fertility levels. Vesicular‐arbuscular mycorrhiza inoculation and P fertility had no effect on inflorescence or flower number, total yield, fruit weight, or crown number. Higher levels of P did not increased total dry shoot weight, total fresh shoot, weight leaf area, total dry root weight, and leaf number in the present of VAM. However, the cultivars responded differently to VAM inoculation. Vesicular‐ arbuscular mycorrhiza inoculation in combination with P at all levels increased total dry and fresh shoot weight, leaf area, and leaf number compared to application of P alone. The results indicated that it may be possible to increase strawberry stolon production by inoculating the strawberry plants with VAM, a technique which might be useful in nurseries to produce certified strawberry plants.     

Effects of vesicular‐arbuscular mycorrhizas and phosphorus on water status and growth of apple

Apple (Malus hupehensis Rehd) seedlings were grown in sterilized and non‐sterilized soil with or without phosphorus (P) added and inoculated by VA mycorrhizal (VAM) fungi (Glomus versifome Daniels et Tappe and Glomus macrocarpum Tul et Tul). In sterilized soil, the VAM infection increased the transpiration rate (Tr.) of the leaves, reduced the stomatal resistance (Sr.) and the permanent wilting percentage (PWP) and enhanced the rate of recovery of the plant from the water stress and the plant growth (e.g. leaf number, stem diameter and dry weight). It also increased absorption of most minerals, especially Zn and Cu by the roots and weakened the P‐Cu and P‐Zn interactions. Phosphorus fertilization had some positive effects on the water status, P nutrition and growth, but it reduced the Cu concentration. VAM improved the water status and enhanced drought tolerance of the trees by enhancing absorption and translocation of water by the external hyphae. The efficiency of inoculation in nonsterile soil was not obvious.     

Effects of vesicular arbuscular mycorrhizal inoculation on growth and phosphorus nutrition of barley in natural or methyl bromide‐treated soil

The growth and phosphorus (P) nutrition of barley (Hordeum vulgare L.) in a soil, methyl bromide fumigated or untreated and supplied with or without mycorrhizal inoculum, was studied in pots placed under a field environment. Inoculation significantly raised the overall levels of vesicular arbuscular mycorrhizal (VAM) infection. The relative increase was significantly greater in sterile than nonsterile soil. Soil sterilization produced significantly higher dry matter throughout the experiment. Inoculation resulted in a significant growth depression earlier in the season which could not be offset by the following mycorrhizal enhancement in P absorption rates. The primary reasons for this yield depression were most probably the root density and available P status of the soil which might have been over the threshold limit for positive mycorrhizal yield response in barley. In this experiment, the result of inoculation could be regarded beneficial considering 17 and 30% higher P concentrations in grain and straw, respectively, but detrimental with respect to 20% loss in grain plus straw yield.     

Acid‐base titration of barley roots

H saturated barley roots were titrated in the presence of 3 different concentrations of KC1. From the observation of the curves obtained, four regions corresponding to ionogenic groups of different pK values are apparent. A CEC of 20 to 30 miliequivalents/100 g dry weight was calculated for barley roots. A pzc value of about 4.5 was found graphically for the root surface.     

Efficiency of h+‐atpase activity on cadmium uptake by four cultivars of lettuce

Cadmium (Cd) uptake by lettuce (Lactuca sativa L.) was studied in a hydroponic solution study at concentrations approaching the total concentration in contaminated soil solutions. Four cultivars of lettuce were tested (Divina, Reine de Mai, Melina, and J.44). Ten 12‐day old seedlings, pretreated in 0.5 μM CdCl₂ solution, were labelled with carrier free ¹⁰⁹CdCl₂ (from 0.05 μM to 5 μM Cd in nutrient solution) in the presence and absence of metabolic inhibitors, DNP and DCCD. Cadmium taken up by the roots was determined after a 30 min desorption in unlabelled CdCl₂ solution. In the absence of metabolic inhibitors and at 5 μM Cd, root absorbed from 2.5 to 8 mg Cd/g root dry weight. Exchangeable Cd measured after desorption represented less than 1% of the total Cd absorbed by the root. Cadmium absorption in presence of DNP showed that approximately 80% of the Cd enters the cell through an active process. This mechanism seems to be directly associated with H⁺‐ATPase as observed with DCCD inhibition. Varietal differences in shoot Cd uptake were only demonstrated at concentrations below 0.1 μM. Screening lettuce cultivars only by the Cd level in the tissue seems not to be possible for these cultivars except at concentrations close to that in the soil solution. But differences in relative contribution of uptake mechanisms in total Cd absorption were observed. High levels of Cd in roots were correlated with high contri‐ butions from H⁺‐ATPase in the active process of Cd uptake.     

Changes in the vesicular‐arbuscular mycorrhizal dependency of Albizia ferruginea and Enterolobium cyclocarpum in response to soil phosphorus concentration 1

A greenhouse experiment was conducted to determine the degree to which Albizia ferruginea and Enterolobium cyclocarpum respond to colonization of their roots by the vesicular‐arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum. Plants were grown in pots containing a subsurface ultisol uninoculated or inoculated with the fungus at three target soil solution phosphorus (P) concentrations. VAMF inoculation enhanced pinnule P content of Albizia but not of Enterolobium at the native P concentration of the experimental soil. However, dry matter yield was not affected by VAMF inoculation for either species. Mycorrhizal inoculation effect was either negative or nil at the highest soil solution P concentration tested. The highest mycorrhizal inoculation effect was observed at soil P concentration of 0.02 mg/L. Based on these data, both Albizia and Enterolobium were classified as highly mycorrhizal dependent species.     

Acid soil tolerances of two wheat cultivars related to soil Ph,KCl‐extractable aluminum and degree of aluminum saturation

Aluminum toxicity, associated with soil acidity, is a major growth‐limiting factor for plants in many parts of the world. More precise criteria are needed for the identification of potential Al toxicity in acid soils. The objective of the current study was to relate the acid soil tolerances of two wheat cultivars to three characteristics of an acid Tatum subsoil (clayey, mixed, thermic, typic Hapludult): pH in a 1:1 soil to water suspension; KCl‐extractable Al; and degree of Al saturation. Aluminum‐tolerant ‘BH 1146’ (Brazil) and Al‐sensitive ‘Sonora 63’ (Mexico) wheat cultivars were grown in greenhouse pots of soil treated with CaCO₃ to establish final soil pH levels of 4.1, 4.6, 4.7, 4.9, 5.2 and 7.3. Soil Al, Ca and Mg were extracted with 1 N KCl, and Al saturation was calculated as KCl‐Al/KCl Al + Ca + Mg%.

Within the soil pH range of 4.1 to 4.9, BH 1146 tops and roots produced significantly more dry matter than did those of Sonora 63; however, at pH 5.2 and 7.3, the top and root yields of the two cultivars were not significantly different. Significant cultivar differences in yield occurred over a range of 36 to 82% saturation of the Tatum soil. Graphs of relative top or root yields against soil pH, KCl‐extractable Al and Al saturation indicated that the two cultivars could be separated for tolerance to Tatum soil under the following conditions: pH less than 5.2 (1:1 soil‐water); KCl‐Al levels greater than 2 c mole kg^‐1 and Al saturations greater than 20%. Results demonstrated that any soil test used to predict Al toxicity in acid soils must take into account the Al tolerances of the plant cultivars involved.     

Diversity of arbuscular mycorrhizal fungi associated with the rhizosphere of tea growing in ‘natural’ and ‘cultivated’ ecosites

The colonization and diversity of arbuscular mycorrhizal fungi (AMF) associated with the rhizosphere of tea [Camellia sinensis (L.) O. Kuntze] growing under ‘natural’ as well as ‘cultivated’ conditions in the Kumaun region of Uttaranchal Himalaya (India), during the periods of active growth and dormancy were investigated. Root and rhizosphere soil samples, collected from both the ecosites (natural and cultivated), were monitored for root colonization. While the percent root colonization was quite high (77.66 ± 4.40 and 86.40 ± 3.02%, in the natural and cultivated tea, respectively) during the period of active growth in both the ecosites, relatively higher colonization (97.33 ± 0.78 and 98.13 ± 0.80%, in the natural and cultivated tea, respectively) was recorded during the period of dormancy. The rhizosphere of cultivated tea bushes was found to be dominated by Glomus morhpotypes (88.89% of the total isolates) along with three morphotypes of Acaulospora; occurrence of 35 morphotypes belonging to four genera viz. Acaulospora (11.43%), Gigaspora (11.43%), Glomus (68.57%) and Scutellospora (8.57%) was recorded in the rhizosphere of tea plants from the natural ecosite. A total of 51 AMF morphotypes were detected. Shannon–Weaver index of diversity was higher (1.80 ± 0.13 and 2.05 ± 0.10 during periods of active growth and dormancy, respectively) at the species level for the natural ecosite over its counterparts from the cultivated ecosite. Values for the diversity indices of natural and cultivated ecosites did not show much variation in the period of dormancy. These data suggest that collectively, various cultural practices negatively affect AMF diversity at the genus level in tea plantations of the colder regions.     

Variation in community structure of arbuscular mycorrhizal fungi associated with a Cu tolerant plant—Elsholtzia splendens

Little is known about the characteristics of arbuscular mycorrhizal fungi (AMF) community in the roots of host plants growing on heavy metal contaminated sites. The objectives of this study were to examine the community structure of AMF associated with the roots of a copper (Cu) tolerant plant—Elsholtzia splendens in a Cu mining area in southeastern Anhui Province, China. Molecular techniques were used to analyze AMF community composition and phylogenetic relationship in E. splendens roots sampled from three Cu mine spoils and two adjacent reference areas. Results obtained showed that root colonization and AMF diversity were very low and negatively correlated with total and extractable Cu concentrations. All the DNA sequences recovered belonged to the genus of Glomus. The principal component analysis (PCA) revealed that the AMF community composition varied remarkably among different sites and was related closely to soil properties, especially Cu concentrations. The distribution pattern of AMF species in various sites suggested the degree of AMF tolerance to Cu contamination. The unique AMF species that presented exclusively in heavily contaminated sites need to be further examined for potential application in phytoremediation of metal contaminated soils.     

Sensitivity of soft red winter wheat cultivars to chlorate‐induced toxicity

The use of chlorate as a nitrate analogue to screen soft red winter wheat (Triticum aestivum L.) cultivars for differences in nitrate reductase activity (NRA) was studied by adding potassium chlorate to a hydroponic nutrient solution in which wheat seedlings were growing. After 14 days, leaf symptoms indicating chlorate‐induced toxicity were rated. It was hypothesized that wheat plants which were susceptible to chlorate‐induced toxicity reduced chlorate and nitrate more rapidly than did resistant plants. In experiments testing the potential of this assay, wheat and barley (Hordeum vulgare L.) cultivars previously reported to have low NRA were less susceptible to chlorate‐induced toxicity than were cultivars reported to have high NRA. The assay was used to screen 15 soft red winter wheat cultivars for differences in sensitivity to chlorate‐induced toxicity. Variable toxic reactions were observed both among and within the cultivars. To determine whether the within‐cultivar variation was environmental or genetic, single plant selections for contrasting chlorate response were made, and bulked progeny were rescreened. In eight of 15 cultivars, the contrasting selections were different for chlorate‐induced toxic response, indicating heterogeneity for this trait within these eight cultivars. These chlorate‐selected lines may also be near‐isogenic lines for NRA. Seedling screening of wheat for chlorate response may be useful for identification of high NRA breeding lines.     

Molecular diversity of arbuscular mycorrhizal fungi associated with an Mn hyperaccumulator—Phytolacca americana,in Mn mining area

Arbuscular mycorrhizal fungi (AMF) have great potential for assisting metal-hyperaccumulating plants in the remediation of contaminated soils. However, little information is available about the symbiosis and community composition of AMF associated with manganese (Mn) hyperaccumulator, such as Phytolacca americana, growing on Mn-contaminated soils under natural conditions. Therefore, the objective of this study was to analyze AMF diversity and community composition in P. americana roots growing at an Mn mining site. Molecular techniques were used to analyze AMF community composition and phylogenetic relationship in P. americana roots sampled from three Mn mine spoils and one adjacent reference areas. Results obtained showed that mycorrhizal symbionts successfully established even in the most heavily Mn-polluted sites. Root colonization and AMF diversity were significantly negatively correlated with total and extractable Mn concentrations. Principal component analysis (PCA) revealed that Mn contamination impacted AMF diversity, and shaped AMF community structure. Phylogenetic analyses demonstrated that all species were affiliated with Glomus, suggesting that Glomus was the dominant genus in this AMF community. Some unique sequences that occurred exclusively in heavily polluted sites associated with P. americana may belong to symbiotic fungi with great potential for improving the phytoremediation efficiency of Mn-contaminated soils.     

Inoculation of pines with mycorrhizal fungi in natural soils—I.: Effects of density and time of application of inoculum and phosphorus amendment on mycorrhizal infection

On two soils lacking fungi capable of forming mycorrhizas with Pinus, the addition of superphosphate at 40 kgP/ha greatly increased mycorrhiza formation in Pinus radiata D. Don and P. elliottii Little and Dorman. Phosphorus could be partially replaced by increasing inoculum density or avoiding delay in inoculation after sowing. Chlamydospores were less effective than basidiospores as inoculum except at the highest density and in the presence of added P. At low available P concn such as are common in Australian soils, the normal pattern of infection of new short roots is interrupted and re-infection from the soil is of greater importance. Survival of mycorrhizal fungi in the soil in the absence of the host may therefore be a critical factor in inoculation programs.     

Effect of PCMBS on calcium‐ or aluminum‐induced curvature in roots of two watermelon cultivars

Unilateral application of calcium (Ca) or aluminum (Al) in agar to the primary roots of watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] cultivars ‘Dixielee’ and ‘Mirage’ induced root curvature. Root curvature induced by Al was greater than that induced by Ca in both cultivars. PCMBS inhibited Al‐induced root curvature in both cultivars, but had no effect on Ca‐induced curvature. The inhibition of curvature indicated that PCMBS reduced Al uptake. ‘Dixielee’ was more responsive to PCMBS than was ‘Mirage’.