Arbuscular mycorrhizal symbiosis changes the colonization pattern of Acacia tortilis spp. Raddiana rhizosphere by two strains of rhizobia

The Endophytic Fungus Phomopsis liquidambari Increases Nodulation and N2 Fixation in Arachis hypogaea by Enhancing Hydrogen Peroxide and Nitric Oxide Signalling

The continuous cropping obstacles in monoculture fields are a major production constraint for peanuts. Application of the endophytic fungus Phomopsis liquidambari has increased peanut yields, and nodulation and N₂ fixation increases have been considered as important factors for P. liquidambari infection-improved peanut yield. However, the mechanisms involved in this process remain unknown. This work showed that compared with only Bradyrhizobium inoculation, co-inoculation with P. liquidambari significantly elevated endogenous H₂O₂ and NO levels in peanut roots. Pre-treatment of seedlings with specific scavengers of H₂O₂ (CAT) and NO (cPTIO) blocked P. liquidambari-induced nodulation and N₂ fixation. CAT not only suppressed the P. liquidambari-induced nodulation and N₂ fixation, but also suppressed the enhanced H₂O₂ and NO generation. Nevertheless, the cPTIO did not significantly inhibit the induced H₂O₂ biosynthesis, implying that H₂O₂ acted upstream of NO production. These results were confirmed by observations that exogenous H₂O₂ and sodium nitroprusside (SNP) reversed the inhibition of P. liquidambari-increased nodulation and N₂ fixation by the specific scavengers. The transcriptional activities of the symbiosis-related genes SymRK and CCaMK of peanut-Bradyrhizobium interactions also increased significantly in response to P. liquidambari, H₂O₂ and SNP treatments. The pot experiment further confirmed that the P. liquidambari infection-enhanced H₂O₂ and NO signalling pathways were significantly related to the increase in peanut nodulation and N₂ fixation. This is the first report that endophytic fungus P. liquidambari can increase peanut-Bradyrhizobium interactions via enhanced H₂O₂/NO-dependent signalling crosstalk, which is conducive to the alleviation of continuous cropping obstacles via an increase in nodulation and N₂ fixation.

Shifts in symbiotic associations in plants capable of forming multiple root symbioses across a long-term soil chronosequence

Changes in soil nutrient availability during long-term ecosystem development influence the relative abundances of plant species with different nutrient-acquisition strategies. These changes in strategies are observed at the community level, but whether they also occur within individual species remains unknown. Plant species forming multiple root symbioses with arbuscular mycorrhizal (AM) fungi, ectomycorrhizal (ECM) fungi, and nitrogen-(N) fixing microorganisms provide valuable model systems to examine edaphic controls on symbioses related to nutrient acquisition, while simultaneously controlling for plant host identity. We grew two co-occurring species, Acacia rostellifera (N2-fixing and dual AM and ECM symbioses) and Melaleuca systena (AM and ECM dual symbioses), in three soils of contrasting ages (c. 0.1, 1, and 120 ka) collected along a long-term dune chronosequence in southwestern Australia. The soils differ in the type and strength of nutrient limitation, with primary productivity being limited by N (0.1 ka), co-limited by N and phosphorus (P) (1 ka), and by P (120 ka). We hypothesized that (i) within-species root colonization shifts from AM to ECM with increasing soil age, and that (ii) nodulation declines with increasing soil age, reflecting the shift from N to P limitation along the chronosequence. In both species, we observed a shift from AM to ECM root colonization with increasing soil age. In addition, nodulation in A. rostellifera declined with increasing soil age, consistent with a shift from N to P limitation. Shifts from AM to ECM root colonization reflect strengthening P limitation and an increasing proportion of total soil P in organic forms in older soils. This might occur because ECM fungi can access organic P via extracellular phosphatases, while AM fungi do not use organic P. Our results show that plants can shift their resource allocation to different root symbionts depending on nutrient availability during ecosystem development.

Sheep manure vermicompost supplemented with a native diazotrophic bacteria and mycorrhizas for maize cultivation

An orthogonal experimental design L9 (3(4)) with 10 repetitions was used to investigate the effect of Glomus claroideum (0, 1 or 2g(-1) plant), G. fasciculatum (0, 1 or 2g plant(-1)), native diazotrophic bacteria (0, 10(3) and 10(5) UFC ml(-1)) and sheep manure vermicompost (0%, 5% and 10% v/v) on maize plant growth, N and P in leaves and mycorrhization percent. Vermicompost explained most of the variation found for leaf number, wet weight, stem height, and diameter. Both mycorrhizas increased the plant wet weight but G. fasciculatum the most. Mycorrhization increased the P content, but not the N content. Mycorrhizal colonization increased when diazotrophic bacteria and vermicompost were added. It was found that weight of maize plants cultivated in peat moss amended with vermicompost increased when supplemented with G. fasciculatum and diazotrophic bacteria.

Optimization of DNA isolation from legume nodules

AIMS

The aim of this study was to optimize DNA extraction from legume nodules to obtain large amounts of high-quality genomic DNA.

METHODS AND RESULTS

Nodules of different legume species were used. Varied concentrations of guanidine thiocyanate (from 6 mol l(-1) to 0.05 mmol l(-1)), a component of DNAzol, were tested. The quality of DNA extract was determined by PCR-RFLP. The best results were obtained with 0.5 mmol l(-1) guanidine thiocyanate, which resulted in greater DNA yield than with higher and lower concentrations or with DNAzol.

CONCLUSION

The procedure using 0.5 mmol l(-1) guanidine thiocyanate yields the highest DNA amount when compared with previously described protocols and offers a reliable method to isolate DNA from nodules of different origins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Irrespective of nodule origin, DNA yield was increased significantly, by two (e.g., Vigna nodules) to seven (Acacia auricoliformis nodules) times. In addition, the proposed procedure's costs are lower than those using the DNAzol.

Ectomycorrhizal symbiosis enhanced the efficiency of inoculation with two Bradyrhizobium strains and Acacia holosericea growth

Two strains of Bradyrhizobium sp., Aust 13C and Aust 11C, were dually or singly inoculated with an ectomycorrhizal fungus, Pisolithus albus to assess the interactions between ectomycorrhizal symbiosis and the nodulation process in glasshouse conditions. Sequencing of strains Aust 13C and Aust 11C confirmed their previous placement in the genus Bradyrhizobium. After 4 months' culture, the ectomycorrhizal symbiosis promoted plant growth and the nodulation process of both Bradyrhizobium strains, singly or dually inoculated. PCR/RFLP analysis of the nodules randomly collected in each treatment with Aust 13C and/or Aust 11C: (1) showed that all the nodules exhibited the same patterns as those of the Bradyrhizobium strains, and (2) did not detect contaminant rhizobia. When both Bradyrhizobium isolates were inoculated together, but without P. albus IR100, Aust 11C was recorded in 13% of the treated nodules compared to 87% for Aust 13C, whereas Aust 11C and Aust 13C were represented in 20 and 80% of the treated nodules, respectively, in the ectomycorrhizal treatment. Therefore Aust 13C had a high competitive ability and a great persistence in soil. The presence of the fungus did not significantly influence the frequencies of each Bradyrhizobium sp. root nodules. Although the mechanisms remain unknown, these results showed that the ectomycorrhizal and biological nitrogen-fixing symbioses were very dependent on each other. From a practical point of view, the role of ectomycorrhizal symbiosis is of great importance to N2 fixation and, consequently, these kinds of symbiosis must be associated in any controlled inoculation.