Dual mycorrhizal associations of jarrah (Eucalyptus marginata) in a nurse-pot system

Jarrah (Eucalyptus marginata Donn ex Sm.) plants, like many other eucalypts, can form symbiotic associations with both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi. To study this tripartite relationship we developed a novel nurse-pot system to allow us to investigate the extent and temporal colonisation dynamics of jarrah by two AM species (Rhizophagus irregularis (Błaszk., Wubet, Renker & Buscot) C. Walker & A. Schüßler comb. nov. and Scutellospora calospora Nicol. & Gerd.) and two putative ECM species (Austroboletus occidentalis Watling & N.M. Greg. and Scleroderma sp.) and their potential effects on jarrah growth and nutrition. Our nurse-pot system, using jarrah as both the nurse plant and test plant, was developed to establish extraradical hyphal networks of both AM and ECM fungi that act as single or dual inoculum for test plants. Mycorrhizal colonisation was described and quantified, and growth and nutritional effects measured and analysed. Mycorrhizal colonisation increased with time for the test seedlings exposed to hyphae networks from S. calospora and Scleroderma sp. The nurse-pot system was effective at initiating colonisation of functioning AM or (putative) ECM systems separately but the ECM symbiosis was inhibited where a dual AM + ECM inoculum (R. irregularis and Scleroderma sp.) was present. The presence of S. calospora, A. occidentalis and Scleroderma sp. individually significantly increased the shoot biomass of seedlings compared with non-mycorrhizal controls. The two AM isolates had different physiological effects on jarrah plants. S. calospora improved growth and micronutrient uptake of jarrah seedlings whereas no positive response was observed with R. irregularis. In addition, as an interesting observation, the non-responsive AM fungus R. irregularis suppressed the ECM symbiosis in dually inoculated plants where ECM structures, positive growth response and nutritional effects were absent. When inoculated individually, ECM isolates dominated the growth response and uptake of P and other nutrients in this dual symbiotic plant. Despite the positive growth response in the A. occidentalis treatment, ECM structures were not observed in either nurse or test seedlings. From the effects of A. occidentalis on jarrah we hypothesise that this fungus forms a functional mycorrhizal-type partnership even without forming archetypal structures in and on the root

Differentiation in populations of the apple scab fungus Venturia inaequalis on cultivars in a mixed orchard remains over time

The ascomycete Venturia inaequalis causes annual epidemics of apple scab worldwide. Scab development is reduced in mixed cultivar orchards compared with monocultures. To use mixtures in commercial production, we need to understand how the population of scab changes in a mixed orchard and how likely a super race, with virulence factors overcoming multiple resistance factors in the mixed orchard, is to emerge and become dominant. We used short sequence repeat (SSR) markers to investigate the temporal change of scab populations in two mixed cultivar orchards in the UK to infer the likelihood of emergence of a scab super race. There were no significant differences between the populations at the two sampling times (six or seven years apart) in either of the two mixed orchards. In one of the orchards apple scab populations on different cultivars were significantly different and the differences did not diminish over time. These results suggest that it is not inevitable that a super race of V. inaequalis will become dominant during the lifetime of a commercial apple orchard.

Effect of a symbiotic on the response to seasonal influenza vaccination is strongly influenced by degree of immunosenescence

Background Ageing increases risk of respiratory infections and impairs the response to influenza vaccination. Pre- and probiotics offer an opportunity to modulate anti-viral defenses and the response to vaccination via alteration of the gut microbiota. This study investigated the effect of a novel probiotic, Bifidobacterium longum bv. infantis CCUG 52486, combined with a prebiotic, gluco-oligosaccharide (B. longum + Gl-OS), on the response to seasonal influenza vaccination in young and older subjects in a double-blind, randomized controlled trial, taking into account the influence of immunosenescence markers at baseline. Results Vaccination resulted in a significant increase in total antibody titres, vaccine-specific IgA, IgM and IgG and seroprotection to all three subunits of the vaccine in both young and older subjects, and in general, the increases in young subjects were greater. There was little effect of the synbiotic, although it tended to reduce seroconversion to the Brisbane subunit of the vaccine and the vaccine-specific IgG response in older subjects. Immunological characterization revealed that older subjects randomized to the synbiotic had a significantly higher number of senescent (CD28-CD57+) helper T cells at baseline compared with those randomized to the placebo, and they also had significantly higher plasma levels of anti-CMV IgG and a greater tendency for CMV seropositivity. Moreover, higher numbers of CD28-CD57+ helper T cells were associated with failure to seroconvert to Brisbane, strongly suggesting that the subjects randomized to the synbiotic were already at a significant disadvantage in terms of likely ability to respond to the vaccine compared with those randomized to the placebo. Conclusions Ageing was associated with marked impairment of the antibody response to influenza vaccination in older subjects and the synbiotic failed to reverse this impairment. However, the older subjects randomized to the synbiotic were at a significant disadvantage due to a greater degree of immunosenscence at baseline compared with those randomized to the placebo. Thus, baseline differences in immunosenescence between the randomized groups are likely to have influenced the outcome of the intervention, highlighting the need for detailed immunological characterization of subjects prior to interventions.

Microbial and biochemical soil quality indicators and their potential for differentiating areas under contrasting agricultural management regimes

The aim of this study was to examine interrelationships between functional biochemical and microbial indicators of soil quality, and their suitability to differentiate areas under contrasting agricultural management regimes. The study included five 0.8 ha areas on a sandy-loam soil which had received contrasting fertility and cropping regimes over a 5 year period. These were organically managed vegetable, vegetable -cereal and arable rotations, an organically managed grass clover ley, and a conventional cereal rotation. The organic areas had been converted from conventional cereal production 5 years prior to the start of the study. All of the biochemical analyses, including light fraction organic matter (LFOM) C and N, labile organic N (LON), dissolved organic N and water-soluble carbohydrates showed significant differences between the areas, although the nature of the relationships between the areas varied between the different parameters, and were not related to differences in total soil organic matter content. The clearest differences were seen in LFOM C and N and LON, which were higher in the organic arable area relative to the other areas. In the case of the biological parameters, there were differences between the areas for biomass-N, ATP, chitin content, and the ratios of ATP: biomass and basal respiration: biomass. For these parameters, the precise relationships between the areas varied. However, relative to the conventionally managed area, areas under organic management generally had lower biomass-N and higher ATP contents. Arbuscular mycorrhizal fungus colonization potential was extremely low in the conventional area relative to the organic areas. Further, metabolic diversity and microbial community level physiological profiles, determined by analysis of microbial community metabolism using Biolog GN plates and the activities of eight key nutrient cycling enzymes, grouped the organic areas together, but separated them from the conventional area. We conclude that microbial parameters are more effective and consistent indicators of management induced changes to soil quality than biochemical parameters, and that a variety of biochemical and microbial analyses should be used when considering the impact of management on soil quality. (C) 2004 Elsevier Ltd. All rights reserved.

Microbial impacts on plant-herbivore interactions: the indirect effects of a birch pathogen on a birch aphid

The role of indirect interactions in structuring communities is becoming increasingly recognised. Plant fungi can bring about changes in plant chemistry which may affect insect herbivores that share the same plant, and hence the two may interact indirectly. This study investigated the indirect effects of a fungal pathogen (Marssonina betulae) of silver birch (Betula pendula) on an aphid (Euceraphis betulae), and the processes underpinning the interaction. There was a strong positive association between natural populations of the aphid and leaves bearing high fungal infection. In choice tests, significantly more aphids settled on leaves inoculated with the fungus than on asymptomatic leaves. Individual aphids reared on inoculated leaves were heavier, possessed longer hind tibiae and displayed enhanced embryo development compared with aphids reared on asymptomatic leaves; population growth rate was also positively correlated with fungal infection when groups of aphids were reared on inoculated branches. Changes in leaf chemistry were associated with fungal infection with inoculated leaves containing higher concentrations of free-amino acids. This may reflect a plant-initiated response to fungal attack in which free amino acids from the degradation of mesophyll cells are translocated out of infected leaves via the phloem. These changes in plant chemistry are similar to those occurring during leaf senescence, and are proposed as the mechanistic basis for the positive interaction between the fungus and aphid.

Exploring the spatial variation of take-all (Gaeumannomyces graminis var. tritici) for site-specific management

The fungus Gaeumannomyces graminis var. tritici (Ggt), commonly known as the take-all fungus, causes damage to roots of wheat and barley that limits crop growth and causes loss of yield. There was little knowledge on the within-field spatial variation of take-all and relations with features in the growing crop, selected soil properties and spectral information from remotely sensed imagery. Geostatistical analyses showed that take-all, chlorosis and leaf area index had similar patchy distributions. Many of the spectral bands from a hyperspectral image also had similar spatial patterns to take-all and chlorosis. Relations between take-all and mineral nitrogen, elevation and pH were generally weaker.

Sequence analysis of the cupin gene family in Synechocystis PCC6803

The recently described cupin superfamily of proteins includes the germin and germinlike proteins, of which the cereal oxalate oxidase is the best characterized. This superfamily also includes seed storage proteins, in addition to several microbial enzymes and proteins with unknown function. All these proteins are characterized by the conservation of two central motifs, usually containing two or three histidine residues presumed to be involved with metal binding in the catalytic active site. The present study on the coding regions of Synechocystis PCC6803 identifies a previously unknown group of 12 related cupins, each containing the characteristic two-motif signature. This group comprises 11 single-domain proteins, ranging in length from 104 to 289 residues, and includes two phosphomannose isomerases and two epimerases involved in cell wall synthesis, a member of the pirin group of nuclear proteins, a possible transcriptional regulator, and a close relative-of a cytochrome c551 from Rhodococcus. Additionally, there is a duplicated, two-domain protein that has close similarity to an oxalate decarboxylase from the fungus Collybia velutipes and that is a putative progenitor of the storage proteins of land plants.

Systemic gut microbial modulation of bile acid metabolism in host tissue compartments

We elucidate the detailed effects of gut microbial depletion on the bile acid sub-metabolome of multiple body compartments (liver, kidney, heart, and blood plasma) in rats. We use a targeted ultraperformance liquid chromatography with time of flight mass-spectrometry assay to characterize the differential primary and secondary bile acid profiles in each tissue and show a major increase in the proportion of taurine-conjugated bile acids in germ-free (GF) and antibiotic (streptomycin/penicillin)-treated rats.Although conjugated bile acids dominate the hepatic profile (97.0 ± 1.5%) of conventional animals, unconjugated bile acids comprise the largest proportion of the total measured bile acid profile in kidney (60.0±10.4%) andheart (53.0 ± 18.5%) tissues. In contrast, in the GF animal, taurine-conjugated bile acids (especially taurocholic acid and tauro-β-muricholic acid) dominated the bile acid profiles (liver: 96.0 ± 14.5%; kidney: 96 ± 1%; heart: 93 ± 1%; plasma: 93.0 ± 2.3%), with unconjugated and glycine-conjugated species representing a small proportion of the profile. Higher free taurine levels were found in GF livers compared with the conventional liver (5.1-fold; P < 0.001). Bile acid diversity was also lower in GF and antibiotic-treated tissues compared with conventional animals. Because bile acids perform important signaling functions, it is clear that these chemical communication networks are strongly influencedbymicrobial activitiesormodulation, as evidenced by farnesoid X receptor-regulated pathway transcripts. The presence of specific microbial bile acid co-metabolite patterns in peripheral tissues (including heart and kidney) implies a broader signaling role for these compounds and emphasizes the extent of symbiotic microbial influences in mammalian homeostasis.

The combined effect of the application of a biocontrol agent Paecilomyces lilacinus, with various practices for the control of root-knot nematodes

The effectiveness of a formulated product containing spores of the naturally occurring fungus Paecilomyces lilacinus, strain 251, was evaluated against root-knot nematodes in pot and greenhouse experiments. Decrease of second-stage juveniles hatching from eggs was recorded by using the bio-nematicide at a dose of 4 kg ha(-1), while a further decrease was recorded by doubling the dose. However, the mortality rate decreased by increasing the inoculum level. Application of P. lilacinus and Bacillus firmus, singly or together in pot experiments, provided effective control of second-stage juveniles, eggs or egg masses of root-knot nematodes. In a greenhouse experiment, the bio-nematicide was evaluated for its potential to control root-knot nematodes either as a stand-alone method or in combination with soil solarization. Soil was solarized for 15 d and the bio-nematicide was applied just after the removal of the plastic sheet. Soil solarization for 15 d either alone or combined with the use of P. lilacinus did not provide satisfactory control of root-knot nematodes. The use of oxamyl, which was applied 2 weeks before and during transplanting, gave results similar to the commercial product containing P. lilacinus but superior to soil solarization. (C) 2007 Elsevier Ltd. All rights reserved.

In vitro evaluation of fibrolytic enzymes as additives for maize (Zea mays L.) silage - II. Effects on rate of acidification, fibre degradation during ensiling and rumen fermentation

A study was carried out to determine the influence of fibrolytic enzymes derived from mesophilic or thermophilic fungal sources, added at ensiling, on time-course fermentation characteristics and in vitro rumen degradation of maize silage. The mesophilic enzyme was a commercial product derived from Trichodenna reesei (L), whereas the thermophilic enzyme was a crude extract produced from Thermoascus aurantiacus (Ta) in this laboratory. The fungus was cultured using maize cobs as a carbon source. The resulting fermentation extract was deionised to remove sugars and characterised for its protein concentration, main and side enzymic activities, optimal pH, protein molecular mass and isoelectric point. In an additional study, both enzymes were added to maize forage (333.5 g DM/kg, 70.0, 469.8, 227.1 and 307.5 g/kg DM of CP, NDF, ADF and starch, respectively) at two levels each, normalized according to xylanase activity, and ensiled in 0.5 kg capacity laboratory minisilos. Duplicate silos were opened at 2, 4, 8, 15, and 60 days after ensiling, and analysed for chemical characteristics. Silages from 60 days were bulked and in vitro gas production (GP) and organic matter degradability (OMD) profiles evaluated using the Reading Pressure Technique (RPT), in a completely randomised design. The crude enzyme extract contained mainly xylanase and endoglucanase activities, with very low levels of exoglucanase, which probably limited hydrolysis of filter paper. The extract contained three major protein bands of between 29 and 55 kDa, with mainly acidic isoelectric points. Ensiling maize with enzymes lowered (P < 0.05) the final silage pH, with this effect being observed throughout the ensiling process. All enzyme treatments reduced (P < 0.05) ADF contents. Treatments including Ta produced more gas (P < 0.05) than the controls after 24 h incubation in vitro, whereas end point gas production at 96 h was not affected. Addition of Ta increased (P < 0.01) OMD after 12 h (410 and 416 g/kg versus 373 g/kg), whereas both L and Ta increased (P < 0.05) OMD after 24 h. Addition of enzymes from mesophilic or thermophilic sources to maize forage at ensiling increased the rate of acidification of the silages and improved in vitro degradation kinetics, suggesting an improvement in the nutritive quality. (C) 2003 Elsevier B.V All rights reserved.

Potential contribution of natural enemies to patterns of local adaptation in plants

Genetic differentiation among plant populations and adaptation to local environmental conditions are well documented. However, few studies have examined the potential contribution of plant antagonists, such as insect herbivores and pathogens, to the pattern of local adaptation. Here, a reciprocal transplant experiment was set up at three sites across Europe using two common plant species, Holcus lanatus and Plantago lanceolata. The amount of damage by the main above-ground plant antagonists was measured: a rust fungus infecting Holcus and a specialist beetle feeding on Plantago, both in low-density monoculture plots and in competition with interspecific neighbours. Strong genetic differentiation among provenances in the amount of damage by antagonists in both species was found. Local provenances of Holcus had significantly higher amounts of rust infection than foreign provenances, whereas local provenances of Plantago were significantly less damaged by the specialist beetle than the foreign provenances. The presence of surrounding vegetation affected the amount of damage but had little influence on the ranking of plant provenances. The opposite pattern of population differentiation in resistance to local antagonists in the two species suggests that it will be difficult to predict the consequences of plant translocations for interactions with organisms of higher trophic levels.

Role of polyhydroxybutyrate and glycogen as carbon storage compounds in pea and bean bacteroids

Rhizobium leguminosarum synthesizes polyhydroxybutyrate and glycogen as its main carbon storage compounds. To examine the role of these compounds in bacteroid development and in symbiotic efficiency, single and double mutants of R. legumosarum bv. viciae were made which lack polyhydroxybutyrate synthase (phaC), glycogen synthase (glgA), or both. For comparison, a single phaC mutant also was isolated in a bean-nodulating strain of R. leguminosarum bv. phaseoli. In one large glasshouse trial, the growth of pea plants inoculated with the R. leguminosarum bv. viciae phaC mutant were significantly reduced compared with wild-type-inoculated plants. However, in subsequent glasshouse and growth-room studies, the growth of pea plants inoculated with the mutant were similar to wildtype-inoculated plants. Bean plants were unaffected by the loss of polyhydroxybutyrate biosynthesis in bacteroids. Pea plants nodulated by a glycogen synthase mutants or the glgA/phaC double mutant, grew as well as the wild type in growth-room experiments. Light and electron micrographs revealed that pea nodules infected with the glgA mutant accumulated large amounts of starch in the II/III interzone. This suggests that glycogen may be the dominant carbon storage compound in pea bacteroids. Polyhydroxybutyrate was present in bacteria in the infection thread of pea plants but was broken down during bacteroid formation. In nodules infected with a phaC mutant of R. leguminosarum bv. viciae, there was a drop in the amount of starch in the II/III interzone, where bacteroids form. Therefore, we propose a carbon burst hypothesis for bacteroid formation, where polyhydroxybutyrate accumulated by bacteria is degraded to fuel bacteroid differentiation.

Soilborne fungi and bacteria symbiotically associated with Steinernema spp. acting as biological agents against Fusarium wilt of tomato

An isolate of Gliocladium virens from disease affected soil in a commercial tomato greenhouse proved highly antagonistic to Fusarium oxysporum f.sp. lycopersici, used together with an isolate of the nematophagus fungus Verticillium chlamydosporium. Significant disease control was obtained when young mycelial preparation (on a food-base culture) of the G. virens together with V. chlamydosporium was applied in potting medium. Similar results were observed when a Trichoderma harzianum isolate was treated in combination with the V. chlamydosporium isolate. Most promising, in terms of minimizing the Fusarium wilt of tomato incidence, was also the effect of the bacteria associated with entomopathogenic nematodes (Steinernema spp.), Pseudomonas oryzihabitans and Xenorhabdus nematophilus.

Biological control of Rhizoctonia solani Damping-off with a bacterium symbiotically associated with Steinernema abbasi

Rhizoctonia solani is a causal agent of damping-off of may cultivated plants. An isolate of the bacterium Pseudomonas oryzihabitans, symbiotically associated with the entomopathogenic nematode Steinernema abbasi, strongly inhibited the pathogen in vitro. The bacterium was firmly attached onto fungus mycelia and degraded the cell walls of the pathogen. In greenhouse experiments, bacterial suspension in sterile water applied in the soil, effectively controlled damping-off of radish.