Measurement of the extraradical mycelium of a vesicular-arbuscular mycorrhizal fungus in soil by chitin determination

Summary Development of a vesicular-arbuscular mycorrhizal (VAM) fungus in association with soybean was determined in a greenhouse soil mix by chitin assay. Samples were sieved to eliminate hexosamine-containing contaminants. This preparation reduced the interference caused by extraneous soil substances and permitted quantitative measurement of extraradical VAM fungal mycelium in the soil mix by colorimetric assay. Recovery of added chitin, used as an internal standard, was greater in the soil mix than in an inert medium indicating that some hexosamine was stabalized from chemical degradation by other soil components.     

Drought resistance of wheat plants inoculated with vesicular-arbuscular mycorrhizae

Summary Drought resistance of wheat (Triticum aestivum L.) as influenced by two vesiculararbuscular mycorrhizal (VAM) fungi,Glomus fasciculatum¹⁰ andGlomus deserticola¹⁹, was evaluated. Soil columns 0.15 m diam. by 1.20 m length were used to reduce the influence of limited rooting space. With initial soil water at 0.5 MPa (0.145 kg kg^–1), plants were subjected to low-level water stress throughout the experiment and severe water stress for 24 h at one (55 days after transplanting, Feekes scale 10.1) two (55 and 63 days, Feekes 10.1 and 10.2), or three (55, 63, and 70 days, Feekes 10.1, 10.1, and 10.2) periods. After each stress period, one set of plants was watered and grown to maturity without subsequent water stress. A second set of plants was harvested 1 week after stress.G. fasciculatum-inoculated plants harvested 7 days after stress at 55 days had greater leaf area and leaf, total plant, and root weight than non-VAM plants.G. deserticola-inoculated plants had greater leaf area and leaf weight than non-VAM plants. After stress at 55 and 63 days, leaf area, and leaf and total dry weight were again greater for VAM than for non-VAM plants. However, after stress at 55, 63, and 70 days, differences in aboveground biomass between VAM and non-VAM plants were not significant at P=0.05. Aboveground biomass was not affected by VAM species in plants stressed at 55 or 55 and 63 days, butG. fasciculatum-inoculated plants produced more tillers atter stress at 55 days. When grown to maturity, VAM plants which had undergone three stress periods had twice the biomass and grain yield as non-VAM plants subjected to the same stress. The three stress periods reduced number of heads and kernel numbers of weight of non-VAM plants compared to VAM plants.G. fasciculatum-inoculated plants consistently had increased root weight and rooting depth.Contribution from the Agricultural Research Service, USDA, in cooperation with the Nebr. Agric. Exp. Stn., Univ. Nebr.-Lincoln, Lincoln, Nebr. Published as Paper No. 7571 Journal Series, Nebr. Agric. Exp. Stn.     

Breeding soybeans for the tropics capable of nodulating effectively with indigenousRhizobium spp.

Summary Most soybean varieties fail to nodulate effectively in tropical soils unless inoculated with a competitive strain ofRhizobium japonicum. Developing countries in the tropics, with few exceptions, lack inoculant industries to produce and distribute viable inoculants to small farmers and extension programs to teach them to use inoculant. Several soybean genotypes have been identified that nodulate effectively with many strains of the cowpea inoculation group which is ubiquitous in tropical soils of Africa. Soybean genotypes that nodulate and grow well without inoculant application are called promiscuous. Methodologies for incorporation of the promiscuity character into high-yielding backgrounds are discussed.Supported in part by grant 05-0560 from United Nations Development Program to the International Institute of Tropical Agriculture.     

The interaction of rockphosphate,Bradyrhizobium, vesicular-arbuscular mycorrhizae and phosphate-solubilizing microbes on soybean grown in a sub-Himalayan mollisol

A factorial design 2³ × 4 with two levels of Mussorie rockphosphate (RP) with or without vesicular-arbuscular mycorrhizal (VAM) fungi and Bradyrhizobium japonicum, and four treatments of phosphate-solubilizing microbes (PSM) Pseudomonas striata, Bacillus polymyxa, Aspergillus awamori was employed using Patharchatta sandy loam soil (Typic Hapludoll). The observations included mycorrhization, nodulation, grain and straw yield, N and P uptake, available soil P and the PSM population in the soil after crop harvest. Inoculation with endophytes alone caused about 70% root colonization. Addition of rockphosphate or inoculation with PSM, except B. polymyxa, stimulated root infection of native as well as introduced VAM endophytes. Application of RP or inoculation with Bradyrhizobium japonicum, mycorrhizal fungi or phosphate-solubilizing microorganisms significantly increased nodulation, N uptake, available soil P and the PSM population in the soil after the crop harvest. The grain and straw yields did not increase following RP addition or mycorrhizal inoculation but increased significantly after inoculation wit Bradyrhizobium or PSM. In general, the application of RP, Bradyrhizobium, VAM and PSM in combinations of any two or three resulted in significant increases in nodulation, plant growth, grain yield and uptake of N and P. Among the four factor interactions, rockphosphate, Bradyrhizobium and P. striata in the absence of VAM resulted in maximal nodulation, grain and straw yields and N uptake by soybean. The highest P uptake by soybean grain was recorded with Bradyrhizobium and A. awamori in the absence of rockphosphate and VAM. Generally, available soil P and PSM population after crop harvest were not significantly increased by the treatment combinations giving the maximal uptake of nutrients. However, they increased significantly in response to PSM, which produced no significant increase in total uptake of nutrients.Research paper no. 7498     

Effect of soil pH and sewage sludge on VA mycorrhizal infection of soybeans

Summary Small plots were amended in 1976 or 1978 with four kinds of sewage sludge. The sludges represented samples considered to be relatively free of heavy metals as well as sludges highly contaminated with heavy metals. Sludges were added to a silt loam soil at rates of 224 or 448 Mgha⁻¹. The soils were maintained at a high or low pH regime. In 1984, soybeans (Glycine max L. Merril. var. ‘Clark’) were planted and grown to the R4 stage. After harvest, roots were removed from the soil, washed, and examined for VA mycorrhizal infection. It was found that the heavy metal content of the sludge alone was generally not related to determining the extent of mycorrhizal infection. A heat treated sludge, high in heavy metals, exhibited the highest degree of mycorrhizal infection when the soil was maintained at a pH of 6.2. With this treatment, 52% of the root segments examined were infected by mycorrhiza. When the same sludge was added to a soil with a slightly lower pH (5.7) none of the roots examined were infected by mycorrhiza. When soybean roots were examined from soils that received no sludge and were maintained at either a low (5.6) or high (6.2) pH, there was no significant difference in mycorrhizal infection between the pH regimes. These results therefore indicate that sewage sludge may inhibit mycorrhizal infection if the sludge contains a high concentration of heavy metals and the sludge is applied to the soil with a low pH. Scientific Article No. A-4093 and Contribution No 7078 of the Maryland Agric. Exp. Stn., Dept. of Agronomy, University of Maryland, College Park, MD 20742.     

Effect of aromatic plant species on vesicular-arbuscular mycorrhizal establishment in Pistacia terebinthus

The inoculation of Pistacia terebinthus with vesicular-arbuscular mycorrhizal (VAM) fungi and the spread of the infection were studied using a mixed cropping system, under glasshouse conditions, with Salvia officinalis, Lavandula officinalis and Thymus vulgaris colonized by Glomus mosseae as an inoculation method. This method was compared with soil inoculum placed under the seed or distributed evenly in the soil. Indirect inoculation with all the aromatic plants tested significantly increased VAM root colonization of P. terebinthus compared with the use of soil inoculum, although the effect on plant growth was different for each one of the aromatic species used as inoculum source. Inoculation with L. officinalis and T. vulgaris were the best treatments resulting in high VAM colonization and growth enhancement of P. terebinthus.     

The effect of vesicular-arbuscular mycorrhizae and chilling on two hybrids of Zea mays L.

In order to investigate the effect of vesicular-arbuscular mycorrhizae on the chilling resistance of Zea mays, seeds of two hybrids (Pioneer 3902 and Pride 5) were grown in soil inoculated with Glomus mosseae. Germination tests at 10° C and 25° C showed that Pride 5 was more resistant to chilling than Pioneer 3902. Plants grown at 25° C for 6 weeks were given a 1-week chilling treatment at 10° C and the responses of mycorrhizal and nonmycorrhizal plants of the two hybrids were compared. At 10° C, the mycorrhizal plants had greater biomass, carbohydrate, and protein content than the nonmycorrhizal plants.     

Root colonization of different hosts by the vesicular-arbuscular mycorrhizal fungus Glomus dimorphicum

Colonization of the roots of beans, alfalfa, onions, red clover, corn, and four barley cultivars (Bonanza, Klondike, Gateway 63, and Olli) by Glomus dimorphicum Boyetchko and Tewari, a vesicular-arbuscular mycorrhizal fungus isolated from a barley field in Alberta, Canada, was studied under greenhouse conditions. Infection levels were low in all four barley cultivars but were higher in beans, alfalfa, and onions and were highest in red clover and corn roots. The infection patterns of G. dimorphicum varied among all the hosts. Coiling of intracellular hyphae occurred in corn, alfalfa, and red clover roots. Appreciable numbers of intraradical vesicles were found only in red clover and bean roots, while arbuscules formed in all hosts except barley. It was concluded that the pattern of root colonization by G. dimorphicum is influenced by the host genome and that the fungal morphology in the roots is variable and, thus, not diagnostic for the mycorrhizal species.     

Effects of phosphate fertilization,lime amendments and inoculation with VA-mycorrhizal fungi on soybeans in an acid soil

Soybeans [Glycine max (L.) Merr. cv. Essex] were grown in nonsterile acid (pH. 5.2) infertile Wynnville silt loam (Glossic Fragiudult) in a glasshouse. The effects of P fertilization and lime were determined by inoculation with two VAM-fungi (VAMF): Glomus fasciculatum (Gf) and Glomus etunicatum (Ge). An important factor affected by the interaction between applied lime (soil acidity), applied P, and VAMF inoculation was the soil Al. Five application rates of P as KH₂PO₄ and three rates of lime were tested. Potassium was equalized with KCl (muriate of potash). P-efficiency (g seed/mg P kg^-1 soil) by vesicular-arbuscular mycorrhiza (VAM) was maximal at 20 mg P kg^-1 soil at all lime and VAMF treatments. VAMF inoculation increased plant survival and protected the soybeans from leaf scorch, thereby substituting for the effects of lime and P. The Ge inoculum was superior in ameliorating leaf scorch in the nonlimed soil. The Gf inoculum required more lime and P than the Ge inoculum to increase seed yield relative to the noninoculated controls containing only native VAMF. Both inocula increased root Al uptake and extractable soil Al in the acid soil without apparent adverse effects on root or shoot. The ability of the VAMF inocula to enhance the efficiency of applied P and decrease seed Cl concentration was increased by lime. Seed yield (Y) was negatively related to seed Cl concentration (X) where Y=aX^-b. Both VAMF inoculation and lime application reduced this negative relationship and may have increased the tolerance to both Cl and soil Al.     

Effects of vesicular-arbuscular mycorrhiza on the size of the labile pool of soil phosphate

Summary Inoculation of lettuce, onion and clover with VA mycorrhizal fungus (Glomus mosseae) increased plant yields and phosphate uptake in three soils that had been depleted in phosphate. From two soils in which the labile pool of phosphate had been labelled with³²P, the specific activity of plant phosphate was the same whether the plants were mycorrhizal or non-mycorrhizal. In a third soil (Sonning) the specific activity was lower in lettuce and clover when the plants were mycorrhizal. When the experiment was repeated with the same soil under conditions that gave lower growth rates, the specific activity was the same in mycorrhizal and non-mycorrhizal plants. The lower specific activity in lettuce and clover in the first experiment is atributed to greater release of slowly exchanging phosphate (which is not in equilibrium with the added³²P), caused by the high uptake of phosphate by the mycorrhizal plants. When they occur, lower specific activities in mycorrhizal plants may therefore not necessarily indicate a solubilizing effect of the mycorrhiza on soil phosphate.     

Influence of vesicular-arbuscular mycorrhiza and straw mulch on growth of barley

Summary The effects of vesicular-arbuscular mycorrhiza (VAM) and of mulching on growth of barley were investigated in a factorial experiment. Plants were grown in cylinders buried in a field in soil with moderate amounts of available phosphate. VAM infection, dry weight and P uptake were determined at harvest after 10 and 161/2 weeks growth.VAM infection was reduced in the upper soil layer by straw mulch, possibly through a reduction in temperature. By the second harvest VAM increased growth by 56% in the non-mulched plots through increased P uptake but VAM did not increase growth in the mulched plots. Mulch increased growth by 85% in the non-mycorrhizal plots, and 28% in the mycorrhizal plots.     

Drought tolerance processes in soybeans

Fifteen soybean cultivars were evaluated in two water supply conditions, inducing or not a drought stress. Main canopy traits were measured several times during the reproductive period and, at maturity date, the yield components were estimated. Using principal components analysis, the main physiological functions involved in soybean drought tolerance are described: leaf cells enlargement and assimilates transport. These processes could be a good basis on which to define new selection criteria for soybean drought tolerance.     

Effects of vesicular-arbuscular mycorrhizae on growth and phosphorus and zinc nutrition of peanut (Arachis hypogaea L.) in an Oxisol from subtropical Australia

Peanut plants (cv. Shulamit) were grown in an Oxisol soil in pots in the glasshouse to assess effects of soil sterilization and inoculation with spores of vesicular-arbuscular mycorrhizal fungi (VAMF) on the response to five rates of phosphorus (0 to 240 kg P ha^–1) and two rates of zinc (0 and 10 kg Zn ha^–1) fertilizers.Both P and Zn nutrition were affected by VAMF activity but the dominant role of VAMF in this soil type was in uptake of P. In the absence of VAMF there was a clear threshold level of P application (60 kg P ha^–1) below which plants grew poorly, which resulted in a sigmoidal response of dry matter to applied P. The maximum response was not fully defined because dry matter production continued to increase up to 240 kg P ha^–1. Tissue P concentration of non-mycorrhizal plants increased linearly with P rate and was always significantly less than that in mycorrhizal plants.Mycorrhizal plants responded without threshold to increasing P rate, attaining maximum dry matter at 120 kg P ha^–1 in inoculated sterilized soil and at 30 kg P ha^–1 in nonsterile soil. These differences in maximal P rates and in the greater dry matter produced in sterile soil at high P rates were attributed to the negative effects of the root-knot nematodeMeloidogyne hapla in nonsterile soil.Plant weight did not respond to zinc fertilizer but tissue Zn concentration increased with applied Zn. Tissue Zn concentration and uptake were increased by VAMF.     

Soil temperature effects on competitiveness and growth ofRhizobium japonicum and on Rhizobium-induced chlorosis of soybeans

Summary The effects of temperature on growth in broth and soil and on competition for nodule formation betweenRhizobium japonicum serotypes USDA 76 and 94 compared to 6 and 110 were studied. Increasing root temperatures of Lee soybean from 20 to 35°C increased the competitiveness of 76 and 94 relative to 6 and 110 for all inoculum ratios such that at 30 and 35°C symptoms ofRhizobium-induced chlorosis appeared. Tolerance to elevated temperatures was exhibited by 76 and 110, but not 94 and 6 in broth and soil which suggested that increased competitiveness of 76 and 94 at high soil temperatures was not dependent upon growth at elevated temperatures. Nodulation and vegetative growth of Lee soybeans were at a minimum at 20°C and optimum at 30°C. Differences in competitiveness of 6 to previous studies indicated the need to standardize temperatures of assays. Differences in growth responses of 76 and 94 to temperature from a previous study suggested a confounding effect on different carbon sources in growth media. Scientific Article No. A-3721 Contribution No. 6697 of the Maryland Agric Exp Sta, Dept of Agronomy, College Park, MD 20742 and the USDA, ARS, Beltsville, MD 20705. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. Degree.     

Conditional lethality involving nuclear and cytoplasmic chlorophyll mutants in soybeans

Summary A conditionally lethal phenotype occurred when a nuclear chlorophyll mutant (y₂₀-k₂) was present with a cytoplasmic chlorophyll mutant (cyt-Y₂) in soybean (Glycine max [L.] Merr.). Nuclear mutant y₂₀-k₂, Genetic Type Collection Number T253, has yellow foliage, tan-saddle-pattern seed and is viable. The y₂₀-k₂ mutant cannot be separated by classical genetic tests into two separate components, y₂₀ (yellow foliage) and k₂ (tan-saddle-pattern seed). Mutant cyt-Y₂, T275, is inherited cytoplasmically, has yellow foliage, and is viable. The genotype cyt-Y₂y₂₀-k₂/ y₂₀-k₂ is a conditional lethal; the genotype is lethal under field conditions, but plants survive under greenhouse conditions. This interaction is unique to y₂₀-k₂. This conditionally lethal genotype may be useful in molecular studies on the interaction between nuclear and plastid genomes.This is a joint contribution of North Central Region, USDA ARS, and Journal Paper No. J-11429 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, and the Agriculture Experiment Station, Univ. of Puerto Rico, Mayaguez Campus, Mayaguez, Puerto Rico 00708. Projects 2471 and 2475. The research was supported in part by the Iowa Soybean Promotion Board.     

Production of vesicular-arbuscular mycorrhizal sporocarps,Glomus aggregatum,on fiberglass screens

Glomus aggregatum was culture onZea mays in sand. Fiberglass screen layers wrapped around the sand medium effectively provided a framework for sporocarp formation, and facilitated the subsequent harvest of the sporocarps.     

Effect of root exudation on VA mycorrhizal infection at early stages of plant growth

Summary No relationship between the degree of VA mycorrhizal infection and total sugar content in root exudates of several plant species of different degree of mycorrhizal susceptibility were observed during the early stages of plant growth. Even more, the non host plants tested showed higher sugar exudation ability, when expressed as the amount exuded per g of root, at these early periods of their growth, than plants susceptible to mycorrhizal infection.Root exudates from host and non host plants influenced similarly the percentage of spore germination and number of secondary spores under controlled conditions.     

Establishment of early instar Heliothis zea on soybeans

Early instar Heliothis zea (Boddie) (Lepidoptera: Noctuidae) established on all stages of soybean (Glycine max [L.] Merrill) tested when larvae were confined to plants, although establishment decreased after podset stage and as seeds matured. In tests where larvae were allowed to disperse freely on plants, establishment also decreased as maturity increased, but was much lower in each stage than when confined to plants. Neonate larvae settled more quickly on terminals and expanding trifoliates than on mature trifoliates based on initiation of feeding and movement away from initial sites of placement. The ability of neonate larvae placed a short distance from soybean plants to reach a host was affected by high soil and ambient temperature. The results of these experiments suggest that larval host establishment and spin-down behavior play a major role in the late instar population distribution among soybean fields and that maturity of the host strongly influences that behavior.

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Résumé Des expériences ont été réalisées dans deux types de conditions (avec ou sans possibilité de dispersion) pour déterminer si le taux d'installation des chenilles de premier stade de H. zea Bod. dépendait d'une mortalité liée au stade développement de Glycine max L. L'installation était considérée comme réussie quand les chenilles avaient atteint le second stade. Bien qu'il fût possible de distinguer les variétés de soja tant par le taux d'installation des chenilles que par les dégâts provoqués, les plantes les plus jeunes étaient plus colonisées par des chenilles que les témoins plus âgés. Toutes les variétés de soja à n'importe quel stade étaient acceptées lorsque la dispersion des chenilles était impossible. Avec possibilité de dispersion, les chenilles ont aussi accepté tous les stades phénologiques, mais en moins grands nombres que lorsque la dispersion était impossible. Le comportement de dispersion était beaucoup plus fréquent sur les plantes à port indéterminé que sur celles à port déterminé. Les possibilités de réinstallation après dispersion des chenilles de premier stade ont été limitées.

     

Identification of quantitative trait loci for plant height, lodging, and maturity in a soybean population segregating for growth habit

The use of molecular markers to identify quantitative trait loci (QTLs) has the potential to enhance the efficiency of trait selection in plant breeding. The purpose of the present study was to identify additional QTLs for plant height, lodging, and maturity in a soybean, Glycine max (L.) Merr., population segregating for growth habit. In this study, 153 restriction fragment length polymorphisms (RFLP) and one morphological marker (Dt1) were used to identify QTLs associated with plant height, lodging, and maturity in 111 F₂-derived lines from a cross of PI 97100 and Coker 237. The F₂-derived lines and two parents were grown at Athens, Ga., and Blackville, S.C., in 1994 and evaluated for phenotypic traits. The genetic linkage map of these 143 loci covered about 1600 cM and converged into 23 linkage groups. Eleven markers remained unlinked. Using interval-mapping analysis for linked markers and single-factor analysis of variance (ANOVA), loci were tested for association with phenotypic data taken at each location as well as mean values over the two locations. In the combined analysis over locations, the major locus associated with plant height was identified as Dt1 on linkage group (LG) L. The Dt1 locus was also associated with lodging. This locus explained 67.7% of the total variation for plant height, and 56.4% for lodging. In addition, two QTLs for plant height (K007 on LG H and A516b on LG N) and one QTL for lodging (cr517 on LG J) were identified. For maturity, two independent QTLs were identified in intervals between R051 and N100, and between B032 and CpTI, on LG K. These QTLs explained 31.2% and 26.2% of the total variation for maturity, respectively. The same QTLs were identified for all traits at each location. This consistency of QTLs may be related to a few QTLs with large effects conditioning plant height, lodging, and maturity in this population.     

Effects of P-fertilization and inoculation by two vesicular-arbuscular mycorrhizal fungi on growth and nodulation ofCalopogonium caeruleum

The growth response ofCalopogonium caeruleum, a leguminous covercrop in plantation agriculture, to inoculation with two vesicular-arbuscular mycorrhizal (VAM) fungi was investigated in five phosphorus (P)-deficient soils supplied with various levels of rock phosphate. Significant shoot yield increases over the uninoculated controls were obtained in most sterilised or unsterilised soils at all applied P levels, although the inoculant VAM fungi differed in their effectiveness in the soils used. Responses in mycorrhizal root infections, P and nitrogen (N) concentrations in tops and plant nodulation varied. The results are discussed in relation to the edaphic environment of the mycorrhizal association.