Changing soil characteristics alter the arbuscular mycorrhizal fungi communities of Arabica coffee (Coffea arabica) in Ethiopia across a management intensity gradient

Coffee is the most important tropical agricultural commodity worldwide, cultivated in more than 70 countries. Despite the plant's huge economic importance, there is very limited knowledge on the association of arbuscular mycorrhizal fungi (AMF) with coffee roots. We investigated the environmental drivers affecting the diversity and community composition of AMF on Arabica coffee in its Ethiopian center of origin. We used 454 amplicon pyrosequencing to describe AMF communities in the roots of Arabica coffee plants that were sampled along a large management intensity gradient, covering the major Ethiopian coffee production systems. We identified AMF genera that have not been reported before in Arabica coffee production regions elsewhere in the world and show that high soil phosphorus availability decreases AMF diversity and that soil pH, nitrogen and phosphorus availability strongly affect AMF community composition. At the scale of our study (max. 82 km distance between sampling points, and 770 m altitude difference), no effect was found of spatial location or altitude on AMF communities. This is the first study analyzing the drivers of naturally occurring AMF in the roots of a globally important tropical crop, providing preliminary data to improve coffee production in its native and introduced range, through targeted intervention in coffee AMF communities.     

Inverse Sequence-tagged Repeat (ISTR) Analysis of Genetic Variability in Forest Coffee (Coffea arabica L.) from Ethiopia

Genetic diversity in forest coffee (Coffea arabica L.) was estimated using inverse sequence-tagged repeat (ISTR) markers. One hundred ninety two samples representing 16 populations of C. arabica from four regions of Ethiopia were analyzed with 12 pairs of forward and backward ISTR primer combinations. A total of 144 reproducible bands were generated out of which 37 (25%) were polymorphic and scored as present (1) or absent (0) data matrix. This data was used to compute Jaccard coefficient to estimate genetic variability among all possible pairs of samples. The proportion of polymorphic bands within populations ranged from 19% for Bale-3, to 54% for Walega-2 populations. Un-weighted pair group method with arithmetic mean (UPGMA) based cluster analysis generated two clusters at 56% similarity value. The samples were clustered on the basis of their geographical origin, which could be attributed to a few region specific banding patterns detected. However, within regions most of the samples failed to cluster on the basis of their respective populations, which may be due to the presence of substantial gene flow between local populations in the form of seedlings carried out by farmers. The results may provide information to develop strategies for in situ conservation.     

Current status of coffee (Coffea arabica L.) genetic resources in Ethiopia: implications for conservation

The aim of this article is to provide an overview of the current situation of coffee genetic resources that are dwindling at an alarming rate in Ethiopia, the centre of diversity of Coffea arabica. Firstly, we describe the coffee growing systems (forest coffee, semi-forest coffee, garden coffee and plantation coffee) and recent research on the genetic diversity of the coffee planting material associated with those systems. Whilst the maximum genetic diversity revealed by DNA-based markers is found in the forest coffees of the south-western highlands, the natural habitat of C. arabica, the taxonomy of coffee landraces is particularly rich in garden coffee systems located in ancient growing zones such as Harerge in eastern Ethiopia. After reviewing the factors involved in the genetic erosion of the Ethiopian genepool, we give an update on the status of coffee genetic resources conserved ex situ in the field genebank of the Jimma Agricultural Research Centre, with 4,780 accessions spread over 10 research stations located in the main production areas, and in the main genebank of the Institute of Biodiversity Conservation located in Choche (Limu) with 5,196 accessions conserved. Lastly, we mention the in situ conservation operations currently being implemented in Ethiopia. Improving our knowledge of the genetic structure of Ethiopian forest and garden coffee tree populations as well as genetic resources conserved ex situ will help to plan the future conservation strategy for that country. To this end, modern tools as DNA-based markers should be used to increase our understanding of coffee genetic diversity and it is proposed, with the support of the international scientific community and donor organizations, to undertake a concerted effort to rescue highly threatened Arabica coffee genetic resources in Ethiopia.

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

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

Field inoculation effectiveness of native and exotic arbuscular mycorrhizal fungi in a Mediterranean agricultural soil

In sustainable agriculture, arbuscular mycorrhizal (AM) fungal inoculation in agronomical management might be very important, especially when the efficiency of native inocula is poor. Here, we assessed the effect of native and exotic selected AM fungal inocula on plant growth and nutrient uptake in a low input Trifolium alexandrinum-Zea mays crop rotation. We evaluated the effects of four exotic AM fungal isolates on T. alexandrinum physiological traits in greenhouse. Then, the field performances of T. alexandrinum inoculated with the exotic AMF, both single and mixed, were compared to those obtained with a native inoculum, using a multivariate analysis approach. Finally, we tested the residual effect of AM fungal field inoculation on maize as following crop. Multivariate analysis showed that the field AM fungal inoculation increased T. alexandrinum and Z. mays productivity and quality and that the native inoculum was as effective as, or more effective than, exotic AM fungal isolates. Moreover, the beneficial effects of AMF were persistent until the second year after inoculation. The use of native AMF, produced on farm with mycotrophic plants species, may represent a convenient alternative to commercial AM fungal inocula, and may offer economically and ecologically important advantages in sustainable or organic cropping systems.     

Assessment of the arbuscular mycorrhizal fungal community in roots and rhizosphere soils of Bt corn and their non-Bt isolines

Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) in combination with sequencing of amplified partial 18S ribosomal DNA was used to assess the effects of transgenic Bt corn 5422Bt1 (event Bt 11) and 5422CBCL (event MON810) on the community structure of a non-target microorganism, namely the arbuscular mycorrhizal fungi (AMF) Glomus in corn roots and rhizosphere soils, relative to their non-Bt isolines 5422 (conventional parent) and 5422wx (conventional hybrid). AMF colonization in roots of different corn genotypes was also assessed using microscopic visualization. No adverse effect was detected on the indigenous AMF colonization of the roots of Bt hybrids 5422Bt1 and 5422CBCL. Two-way indicator species analysis (TWINSPAN^®) and detrended correspondence analysis (DCA) of the DGGE data from corn roots presented differences between Bt and non-Bt corn isolines (5422Bt1 vs. 5422wx, and 5422CBCL vs. 5422wx). However, differences were also recognized between the two non-Bt corn cultivars (5422 vs. 5422wx), and between the two Bt corn lines (5422Bt1 vs. 5422CBCL) in roots. Our results suggest that corn genotypes may have a greater influence on the AMF community structure of plant roots and rhizosphere soils than other factors, such as the age of the growing plants.     

Community structure of arbuscular mycorrhizal fungi associated with Robinia pseudoacacia in uncontaminated and heavy metal contaminated soils

The significance of arbuscular mycorrhizal fungi (AMF) in soil remediation has been widely recognized because of their ability to promote plant growth and increase phytoremediation efficiency in heavy metal (HM) polluted soils by improving plant nutrient absorption and by influencing the fate of the metals in the plant and soil. However, the symbiotic functions of AMF in remediation of polluted soils depend on plant–fungus–soil combinations and are greatly influenced by environmental conditions. To better understand the adaptation of plants and the related mycorrhizae to extreme environmental conditions, AMF colonization, spore density and community structure were analyzed in roots or rhizosphere soils of Robinia pseudoacacia. Mycorrhization was compared between uncontaminated soil and heavy metal contaminated soil from a lead–zinc mining region of northwest China. Samples were analyzed by restriction fragment length polymorphism (RFLP) screening with AMF-specific primers (NS31 and AM1), and sequencing of rRNA small subunit (SSU). The phylogenetic analysis revealed 28 AMF group types, including six AMF families: Glomeraceae, Claroideoglomeraceae, Diversisporaceae, Acaulosporaceae, Pacisporaceae, and Gigasporaceae. Of all AMF group types, six (21%) were detected based on spore samples alone, four (14%) based on root samples alone, and five (18%) based on samples from root, soil and spore. Glo9 (Rhizophagus intraradices), Glo17 (Funneliformis mosseae) and Acau3 (Acaulospora sp.) were the three most abundant AMF group types in the current study. Soil Pb and Zn concentrations, pH, organic matter content, and phosphorus levels all showed significant correlations with the AMF species compositions in root and soil samples. Overall, the uncontaminated sites had higher species diversity than sites with heavy metal contamination. The study highlights the effects of different soil chemical parameters on AMF colonization, spore density and community structure in contaminated and uncontaminated sites. The tolerant AMF species isolated and identified from this study have potential for application in phytoremediation of heavy metal contaminated areas.     

干旱胁迫下丛枝菌根对大豆抗氧化代谢及根围微生物的影响

丛枝菌根真菌(AMF)可促进作物营养吸收和提高抗逆性,成为寄主抵御干旱胁迫的有效途径。为探明AMF提高大豆抗旱性的机制,以‘桂春豆103’为材料接种幼套近明囊霉(Claroideoglomus etunicatum,简写为C.e),研究干旱条件下C.e对田间大豆叶抗氧化酶及根围土中C/N/P循环相关酶活性等的影响,并用变性梯度凝胶电泳等方法探索土壤微生物群落结构的变化。结果表明:干旱处理前,接种C.e(+AM)处理大豆SOD、POD活性及游离脯氨酸(FP)含量,磷酸酶、蔗糖酶和脲酶活性,土壤细菌、真菌和放线菌数量及物种多样性、丰富度和群落均匀度指数,大豆生物量和株高均显著高于(-AM)处理(P0.05),MDA含量显著降低(P0.05)。干旱(D)处理后,+AM+D处理的上述各项指标,除MDA含量比-AM+D或+AM处理分别显著降低或升高(P0.05),FP含量比两处理显著提高(P0.05)外,其余指标值及细菌和真菌r DNA条带数均比-AM+D处理显著升高,比+AM处理显著下降(P0.05)。-AM+D与-AM处理的细菌和真菌群落均分别聚类于两不同分支,+AM与+AM+D处理聚于同一分支。可见,+AM+D处理能显著促进大豆抗氧化酶系统活性,维持较强的活性氧清除和渗透调节能力,缓解干旱对土壤酶活性的抑制,保持较高的细胞膜稳定性、土壤微生物数量和群落多样性,有利于C/N/P循环转化,提高抗旱性,最终促进大豆生长。本研究可为促进农业生态系统可持续发展奠定基础。     

Co-selection of compatible rhizobia and vesicular-arbuscular mycorrhizal fungi for cowpea in sterilized and non-sterilized soils

Summary We selected two isolates of Rhizobium for cowpea (Vigna unguiculata) with sterilized soil tests and two different isolates by non-sterilized soil testing. The four rhizobia were then paired individually with either Glomus pallidum, Glomus aggregatum, or Sclerocystis microcarpa in separate, sterilized, or non-sterilized soil experiments. The purpose of the experiments was to determine the effect of soil sterilization on the selection of effective cowpea rhizobia, and to see whether these rhizobia differed in their effects on cowpea growth when paired with various vesicular-arbuscular mycorrhizal (VAM) fungi. Our experiments showed that the rhizobia selected in sterilized soil tests produced few growth responses in the cowpea compared to the other introduced rhizobia, irrespective of pairing with VAM fungi in sterilized or non-sterilized soil. In contrast, the two rhizobia initially selected by non-sterilized soil testing significantly improved cowpea growth in non-sterilized soil, especially when paired with G. pallidum. Our results suggest that it is important to select for effective rhizobia in non-sterilized soil, and that pairing these rhizobia with specific, coselected VAM fungi can significantly improve the legume growth response.     

Growth and interactions of arbuscular mycorrhizal fungi in soils from limestone and acid rock habitats

Arbuscular mycorrhizal (AM) development in different soil types, and the influence of AM fungal hyphae on their original soil were investigated. Plantago lanceolata, which can grow in soils of a very wide pH range, was grown in two closely related limestone soils and an acid soil from rock habitats. Plants were colonised by the indigenous AM fungal community. The use of compartmented systems allowed us to compare soil with and without mycorrhizal hyphae. Root colonisation of P. lanceolata was markedly higher in the limestone soils (30-60%) than in the acid soil (5-20%), both in the original habitat and in the experimental study. Growth of extraradical AM fungal hyphae was detected in the limestone soils, but not in the acid soil, using the signature fatty acid 16:1ω5 as biomass indicator. Analysis of signature fatty acids demonstrated an increased microbial biomass in the presence of AM fungal hyphae as judged for example from an increased amount of NLFA 16:0 with 30 nmol g⁻¹ in one of the limestone soils. Bacterial activity, but not soil phosphatase activity, was increased by around 25% in the presence of mycorrhizal hyphae in the first harvest of limestone soils. AM fungal hyphae can thus stimulate microorganisms. However, no effect of AM hyphae was observed on the soil pH or organic matter content in the limestone soils and the available P was not depleted.     

Nitrogen capture by grapevine roots and arbuscular mycorrhizal fungi from legume cover-crop residues under low rates of mineral fertilization

The influence of mineral fertilization on root uptake and arbuscular mycorrhizal fungi-mediated ¹⁵N capture from labeled legume (Medicago polymorpha) residue was examined in winegrapes (Vitis vinifera) in the greenhouse, to evaluate compatibility of fertilization with incorporation of cover-crop residue in winegrape production. Plants grown in marginal vineyard soil were either fertilized with 0.25× Hoagland’s solution or not. This low fertilization rate represents the deficit management approach typical of winegrape production. Access to residue in a separate compartment was controlled to allow mycorrhizal roots (roots + hyphae), hyphae (hyphae-intact), or neither (hyphae-rotated) to proliferate in the residue by means of mesh core treatments. Leaves were weekly analyzed for ¹⁵N. On day 42, plants were analyzed for ¹⁵N and biomass; roots were examined for intraradical colonization; and soils were analyzed for ¹⁵N, inorganic N, Olsen-P, X-K, and extraradical colonization. As expected, extraradical colonization of soil outside the cores was unaffected by mesh core treatment, while that inside the cores varied significantly. ¹⁵N atom% excess was highest in leaves of roots + hyphae. In comparison, leaf ¹⁵N atom% excess in hyphae-intact was consistently intermediate between roots + hyphae and hyphae-rotated, the latter of which remained unchanged over time. Fertilization stimulated host and fungal growth, based on higher biomass and intraradical colonization of fertilized plants. Fertilization did not affect hyphal or root proliferation in residue but did lower %N derived from residue in leaves and stems by 50%. Our results suggest that even low fertilization rates decrease grapevine N uptake from legume crop residue by both extraradical hyphae and roots.     

Diversity of halophytes and identification of arbuscular mycorrhizal fungi colonising their roots in an abandoned and sustained part of Sečovlje salterns

Sečovlje salterns are an important protected area of biotic diversity in the Mediterranean. They represent an extreme environment with high salinity and drought that severely influence the growth of organisms. In the present study, diversity of plant halophytes and their mycorrhizal status were screened at eight different locations, which were mostly dikes and salt ponds, and which were deliberately selected for their distinct properties (e.g. soil salinity ranging from 105 to 2627 μS cm⁻¹, vegetation type and management practice of the salterns).Twelve different halophytic plant species were recorded, of which eleven are designated as vulnerable. With few exceptions, they were found at the abandoned (Fontanigge) and sustained (Lera) locations of the Sečovlje salterns, distributed according to their tolerance to the salinity and waterlogging. The highest diversity of halophytes was listed at Fontanigge, in the abandoned, periodically flooded and gradually overgrown salt ponds. All of the examined species were colonised with either arbuscular mycorrhizal fungi (AMF) and/or dark septate endophytes (DSEs). High levels of colonisation were however detected only for species belonging to the Asteraceae and Plantaginaceae families. Higher root colonisation frequencies were generally seen for plants growing in the abandoned parts, when compared to the managed parts, whereas there was little correlation of the colonisation parameters with physicochemical parameters of rhizospheric soil properties.Molecular analysis by temporal temperature gradient gel electrophoresis (TTGE) of roots of halophytic plant species with confirmed AMF colonisation (arbuscules present) revealed the occurrence of at least six different AMF species, related to Glomus geosporum, Glomus caledonium and Glomus intraradices, and to different Glomus sp. clades and the Diversispora clade. This is to the best of our knowledge the first report of AMF and DSE mycorrhizal status of most of the halophyte plant species examined and of the brother scale identification of AMF species based on molecular analyses of roots of diverse halophytes from high saline environments.     

多胺对共生条件下丛枝菌根真菌及宿主植物生长发育的影响

为探讨多胺对共生条件下丛枝菌根真菌及其宿主植物生长发育的影响,本研究以丛枝菌根真菌(Gigaspora margarita)为试验材料,通过施用不同浓度的多胺(Polyamine,PA)及其生物合成抑制剂[Methylglyoxal bis(guanylhydrazone),MGBG]处理接种丛枝菌根真菌的葡萄微繁苗,研究共生培养条件下外源多胺及多胺合成抑制剂对丛枝菌根真菌孢子萌发、芽管菌丝及其宿主植物生长发育的影响.试验结果表明,共生培养条件下,一定浓度的外源PA对丛枝菌根真菌及其宿主植物的生长发育具显著促进作用,丛枝菌根真菌孢子数、菌丝长度、侵染率、丛枝丰富度及菌根化葡萄幼苗生长势均显著提高.MGBG则表现较强的抑制作用.且该抑制作用可被外源PA部分解除,证明外源多胺对菌根化葡萄微繁苗生长发育的促进作用是通过活化根系土壤中丛枝菌根真菌,促进微繁苗丛枝菌根共生体的良好发育,最大程度地发挥菌根化效应得以表现的.     

Consumption of mycorrhizal and saprophytic fungi by Collembola in grassland soils

Although soil-dwelling Collembola can influence plant growth and nutrient cycling, their specific role in soil food webs is poorly understood. Soil-free microcosm studies suggest that Collembola are primarily fungivores where they feed preferentially on saprophytic fungi (SF) over other fungal types. We directly assessed collembolan consumption of arbuscular mycorrhizal fungi (AMF) and SF using plant-soil mesocosms and natural abundance stable carbon isotope techniques. Mycorrhizal Andropogon gerardii (C₄ grass) seedlings were placed in pots containing Collembola and soil from a C₃ plant dominated site, while mycorrhizal Pascopyrum smithii (C₃ grass) seedlings were placed in pots with Collembola and soil collected at a C₄ plant dominated site. After 6 weeks, collembolans assimilated carbon derived from C₃ and C₄ sources in both A. gerardii and P. smithii treatments. Comparing Collembola isotope values in AMF vs. AMF-suppressed treatments, our data show that both AMF and SF were consumed in these experimental soil environments.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.     

The effect of vesicular-arbuscular mycorrhizal inoculation on nutrient uptake and yield of alley-cropped cassava in a degraded Alfisol of southwestern Nigeria

Leaf and root (tuber) nutrient uptake patterns of cassava (Manihot esculenta Crantz) alley-cropped with gliricidia (Gliricidia sepium), leucaena (Leucaena leucocephala), and senna [(Senna (syn. Cassia) siamea] as influenced by vesicular-arbuscular mycorrhizal (VAM) inoculation in a degraded Alfisol were investigated in consecutive years. The cassava plants were mulched with fresh prunings of each hedgerow tree species at 2-month intervals in the second and third years of alley cropping. While VAM inoculation significantly influenced the root uptake of nutrients, the leaf uptake was not affected except for the uptake of P. In most cases, there was no difference in the nutrient concentration between inoculated and uninoculated plants, either in the leaf or in the root, indicating that the productivity of cassava was regulated by the amount of nutrients the roots could absorb. In spite of similar total soil N in all inoculated and uninoculated alley-cropped cassava plots and similar exchange-able soil K contents in inoculated and uninoculated alley-cropped cassava plots with leucaena and senna, greater uptake of N, P, and K and greater concentrations of K were observed in roots of inoculated alley-cropped cassava with gliricidia and leucaena than with senna. These results indicated that greater mineralization and availability of nutrients to cassava roots from prunings of nodulating gliricidia and leucaena than from non-nodulating senna may be important, particularly with efficient VAM inoculation, in these alley-cropping systems. Also, for similar nutrients in the inoculated and uninoculated cassava soils alley-cropped with each hedgerow species, VAM inoculation significantly enhanced cassava root dry weights, indicating that an effective VAM fungus can be an agent of greater nutrient uptake in a competitive environment.     

Response of soybean cultivars toward inoculation with three arbuscular mycorrhizal fungi and Bradyrhizobium japonicum in the alluvial soil

The aim of this study was to assess the comparative efficacy of three arbuscular mycorrhizal fungi (AMF) combined with cultivar specific Bradyrhizobium japonicum (CSBJ) in soybean under greenhouse conditions. Soybean seeds of four cultivars namely JS 335, JS 71-05, NRC 2 and NRC 7 were inoculated with three AM fungi (Glomus intraradices, Acaulospora tuberculata and Gigaspora gigantea) and CSBJ isolates, individually or in combination, and were grown in pots using autoclaved alluvial soil of a non-legume cultivated field of Ajmer (Rajasthan). Assessment of the data on nodulation, plant growth and seed yield revealed that amongst the single inoculations of three AMF, G. intraradices produced the largest increases in the parameters studied followed by A. tuberculata and G. gigantea indicating that plant acted selectively on AMF symbiosis. The dual inoculation with AMF + CSBJ further improved these parameters demonstrating synergism between the two microsymbionts. Among all the dual treatments, G. intraradices + B. japonicum brought about the largest increases in the studied characteristics particularly in seed weight per plant that increased up to 115.19%, which suggested that a strong selective synergistic relationship existed between AMF and B. japonicum. The cv. JS 335 exhibited maximum positive response towards inoculation. The variations in efficacy of different treatments with different soybean cultivars indicate the specificity of the inoculation response. These results provide a basis for selection of an appropriate combination of specific AMF and Bradyrhizobium which could further be utilized for verifying the symbiotic effectiveness and competitive ability of microsymbionts under field conditions of Ajmer region.     

Arylsulphatase activity of different latosol soils of Ghana cropped to cocoa (Theobroma cacao) and coffee (Coffea canephora var. robusta)

Summary A study was undertaken to investigate arylsulphatase activity in 15 soils cropped to cocoa (Theobroma cacao) and coffee (Coffea canephora var. robusta) in Ghana. The arylsulphatase activity was correlated positively and significantly with organic C, total N, and cation exchange capacity, and correlated negatively with acetate soluble sulphate. The enzyme was deactivated at an incubation temperature of over 60°C. Preheating and oven-drying of soils decreased arylsulphatase activity. Addition of 1.0 ml toluene during the assay resulted in a sharp decline in arylsuphatase activity. The addition of trace elements at a concentration of 1 ppm caused a reduction in soil arylsulphatase activity compared with that of the untreated samples.     

Growth response of field-grown Siratro (Macroptilium atropurpureum Urb.) and Aeschynomene american L. to inoculation with selected vesicular-arbuscular mycorrhizal fungi

Summary The effect of inoculation with a selected isolate of Glomus etunicatum Becker and Gerdemann and one of G. intraradices Schenck and Smith on the growth and nutrient content of Macroptilium atropurpureum Urb. cv. Siratro and Aeschynomene americana L., at applied P levels of 10, 30, 60, and 120 kg ha^-1, was studied under field conditions. At all P levels and for all harvests, the shoot dry mass of Siratro and A. americana were greater for the plants inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungi than the control plants. Differences between the VAM fungus-inoculated and the control plants were most marked between 30 and 90 kg ha^-1 of applied P and diminished at 120 kg ha^-1. At the first harvest of Siratro, the plants inoculated with G. etunicatum had a greater shoot dry mass than those inoculated with G. intraradices, for all levels of applied P. However, for subsequent harvest of Siratro and for the one harvest of A. americana the response of shoot dry mass to the two VAM fungi was equivocal. Fungal inoculation gave at least a 30% saving in the amount of P fertilizer required (40 kg ha^-1) for the maximum yield. The plants inoculated with VAM fungi had a greater tissue concentration and total content of P and N than the control plants at low and intermediate levels of applied P. The percentage of root colonized by VAM fungi for the inoculated plants of the two legumes increased linearly with P additions up to 60 kg ha^-1. The conclusion is that under amended (limed and fertilized) soil conditions, inoculation with selected VAM fungi can improve the establishement and growth of forage legumes in fields that contain ineffective populations of native VAM fungi.     

Influence of arbuscular mycorrhizal fungi and salinity on growth,biomass, and mineral nutrition of<Emphasis Type="Italic"> Acacia auriculiformis</Emphasis>

The effect of salinity on the efficacy of two arbuscular mycorrhizal fungi, Glomus fasciculatum and G. macrocarpum, alone and in combination was investigated on growth, development and nutrition of Acacia auriculiformis. Plants were grown under different salinity levels imposed by 0.3, 0.5 and 1.0 S m^-1 solutions of 1 M NaCl. Both mycorrhizal fungi protected the host plant against the detrimental effect of salinity. The extent of AM response on growth as well as root colonization varied with fungal species, and with the level of salinity. Maximum root colonization and spore production was observed with combined inoculation, which resulted in greater plant growth at all salinity levels. AM fungal inoculated plants showed significantly higher root and shoot weights. Greater nutrient acquisition, changes in root morphology, and electrical conductivity of soil in response to AM colonization was observed, and may be possible mechanisms to protect plants from salt stress.