Arbuscular Mycorrhizal Endophyte Research Articles

Arbuscular mycorrhizas are present on Spitsbergen.

A previous study of 76 plant species on Spitsbergen in the High Arctic concluded that structures resembling arbuscular mycorrhizas were absent from roots. Here, we report a survey examining the roots of 13 grass and forb species collected from 12 sites on the island for arbuscular mycorrhizal (AM) colonisation. Of the 102 individuals collected, we recorded AM endophytes in the roots of 41 plants of 11 species (Alopecurus ovatus, Deschampsia alpina, Festuca rubra ssp. richardsonii, putative viviparous hybrids of Poa arctica and Poa pratensis, Poa arctica ssp. arctica, Trisetum spicatum, Coptidium spitsbergense, Ranunculus nivalis, Ranunculus pygmaeus, Ranunculus sulphureus and Taraxacum arcticum) sampled from 10 sites. Both coarse AM endophyte, with hyphae of 5-10μm width, vesicles and occasional arbuscules, and fine endophyte, consisting of hyphae of 1-3μm width and sparse arbuscules, were recorded in roots. Coarse AM hyphae, vesicles, arbuscules and fine endophyte hyphae occupied 1.0-30.7, 0.8-18.3, 0.7-11.9 and 0.7-12.8% of the root lengths of colonised plants, respectively. Principal component analysis indicated no associations between the abundances of AM structures in roots and edaphic factors. We conclude that the AM symbiosis is present in grass and forb roots on Spitsbergen.

Influence of Arbuscular Mycorrhizal Fungus and Kinetin on the Response of Mungbean Plants to Irrigation by Seawater

An experiment was carried out to investigate the effects of pre-inoculation with the mycorrhizal fungus Glomus clarum and foliar application of kinetin on the growth of mungbean plant irrigated wht different dilutions of seawater. Arbuscular-mycorrhizal (AM) infection significantly increased dry weight, height, chlorophyll, sugar and protein content, nitrogen and phosphorus-use efficiencies, leaf conductivity, transpiration rate, nitrogenase, acid and alkaline phosphates activities of all salinized mungbean plants in comparison with control and non-mycorrhizal plants irrespective of the presence or absence of kinetin. Mycorrrhizal plants showed higher concentrations of N, P, K, Ca and Mg and lower Na/N, Na/P, Na/K, Na/Ca and Na/ Mg ratios than non-mycorrhizal plants when irrigated with certain dilutions of seawater Mungbean plants showed 597% and 770% dependency on AM fungus G. clarum in absence and presence of kinetin, respectively, for biomass production under a level of 30% of seawater. The average value of tolerance index for mycorrhizal plants accounted 267% and 364% in absence and presence kinetin respectively. This study provides evidence for the benefits of kinetin which are actually known for mycorrhizal than non-mycorrhzal plants. AM fungus and kinetin protected the host plants against the detrimental effects of salt. However, mycorrhizal infection was much more effective than kinetin applications. Thus management applications of this arbuscular mycorrhizal endophyte (G. clarum) with kinetin could be of importance in using seawater in certain dilutions for irrigation in agriculture.

Influence of arbuscular-mycorrhizal fungi, Rhizobium meliloti strains and PGPR inoculation on the growth of Medicago arborea used as model legume for re-vegetation and biological reactivation in a semi-arid mediterranean area

Medicago arborea can be used for re-vegetationpurposes under semiarid conditions. These woody legumes have the ability toforman association with arbuscular mycorrhizal (AM) fungi and rhizobial bacteria,which can be maximised by microorganisms producing certain stimulatingmetabolites acting as plant growth promoting rhizobacteria (PGPR). The effectsof single and combined inoculations using microorganisms with different andinteractive metabolic capacities, namely three Glomusspecies, two Rhizobium meliloti strains (a wild type, WTand its genetically modified derivative GM) and a plant growth promotingrhizobacterium, (PGPR), were evaluated. All three inoculated AM fungi affectedMedicago growth in different ways. Differences weremaintained when soil was co-inoculated with each of the rhizobial strains (WTorGM) and the PGPR. Mycorrhizal fungi were effective in all cases, but the PGPRonly affected plant growth specific microbial situations. PGPR increased growthof G. mosseae-colonised plants associated withRhizobium WT strain by 36% and those infected byG. deserticola when associated with the rhizobial GMstrainby 40%. The most efficient microbial treatments involved mycorrhizalinoculation, which was an indication of the AM dependency of this plantspecies.Moreover, PGPR inoculation was only effective when associated with specificmycorrhizal endophytes (G. mosseae plus WT andG.deserticola plus GM rhizobial strain). The reduced root/shoot (R/S)ratio resulting from PGPR inoculation, was an indication of more effective rootfunction in treated plants. AM colonisation and nodule formation wereunaffectedby the type of AM fungus or bacteria (rhizobial strain and/or PGPR). AM fromnatural soil were less infective and effective than those from the collection.The results supported the existence of selective microbial interactionsaffecting plant performance. The indigenous AM fungi appeared to be ineffectiveand M. arborea behaved as though it was highly dependentonAM colonisation, which implied that it must have a mycorrhizal association toreach maximum growth in the stressed conditions tested. Optimum growth ofmycorrhizal M. arborea plants was associated with specificmicrobial groups, accounting for a 355% increase in growth overnodulatedcontrol plants. The beneficial effect of PGPR in increasing the growth of awoody legume, such as M. arborea under stress, was onlyobserved with co-inoculation of specific AM endophytes. As a result of theinteraction, only shoot biomass was enhanced, but not as a consequence ofenhancing of the colonising abilities of the endophytes. The growthstimulation,occurring as a consequence of selected microbial groups, may be critical anddecisive for the successful establishment of plants under Mediterraneanclimaticand soil conditions.

Plant growth and root system morphology of Olea europaea L. rooted cuttings as influenced by arbuscular mycorrhizas

SummaryThe effects of arbuscular mycorrhizal (AM) fungi on plant development and root system morphology of different cultivars of Olea europaea were investigated. Rooted cuttings of olive cvs Frantoio, Muraiolo and Leccino at the beginning of the rooting phase, were inoculated with the AM endophyte Glomus mosseae. After six monthly growth increments, the percentage of root colonization and the root system morphology of the rooted cuttings were evaluated. AM inoculation enhanced growth of olive plants compared with the controls, inducing a different behaviour of the three olive cultivars colonized by G. mosseae. The fungal symbiont mainly increased the growth of the rooted cuttings Moraiolo ‘of’ and ‘Frantoio’, whereas ‘Leccino’ plants showed no significant differences from the controls. Staining of root samples of the cuttings indicated differences in the percentage of AM root colonization depending on cultivar. ‘Moraiolo’ root systems showed significantly less root length infected by Glomus mosseae compared with the other two cultivars. The morphometric analysis of olive roots demonstrated that colonization by AM fungi can significantly alter root system morphology. Colonization increased the intensity of branching on lateral orders in all cultivars and greatly increased the proportion of higher order laterals in the root system. The overall effect of mycorrhizas was, consequently, to increase lateral root frequency, giving rise to a more branched root system. Moreover the results show that such an increase in branching could be due in part to a better nutrition of mycorrhizal plants whereas mycorrhizal colonization and cultivar type greatly influenced the rooting pattern. These results show that mycorrhizal symbiosis can not only result in a significant increase in plant growth but can also alter olive root system morphology, positively affecting the establishment of plantlets.

Improvement of Arbuscular Mycorrhiza Development by Inoculation of Soil with Phosphate-Solubilizing Rhizobacteria To Improve Rock Phosphate Bioavailability ((sup32)P) and Nutrient Cycling

The interactive effect of phosphate-solubilizing bacteria and arbuscular mycorrhizal (AM) fungi on plant use of soil P sources of low bioavailability (endogenous or added as rock phosphate [RP] material) was evaluated by using soil microcosms which integrated (sup32)P isotopic dilution techniques. The microbial inocula consisted of the AM fungus Glomus intraradices and two phosphate-solubilizing rhizobacterial isolates: Enterobacter sp. and Bacillus subtilis. These rhizobacteria behaved as "mycorrhiza helper bacteria" promoting establishment of both the indigenous and the introduced AM endophytes despite a gradual decrease in bacterial population size, which dropped from 10(sup7) at planting to 10(sup3) CFU g(sup-1) of dry rhizosphere soil at harvest. Dual inoculation with G. intraradices and B. subtilis significantly increased biomass and N and P accumulation in plant tissues. Regardless of the rhizobacterium strain and of the addition of RP, AM plants displayed lower specific activity ((sup32)P/(sup31)P) than their comparable controls, suggesting that the plants used P sources not available in their absence. The inoculated rhizobacteria may have released phosphate ions ((sup31)P), either from the added RP or from the less-available indigenous P sources, which were effectively taken up by the external AM mycelium. Soluble Ca deficiency in the test soil may have benefited P solubilization. At least 75% of the P in dually inoculated plants derived from the added RP. It appears that these mycorrhizosphere interactions between bacterial and fungal plant associates contributed to the biogeochemical P cycling, thus promoting a sustainable nutrient supply to plants.

Interaction between Alternaria alternata or Fusarium equiseti and Glomus mosseae and its effects on plant growth

The effect of inoculation with the saprophytic fungi Alternaria alternata or Fusarium equiseti on maize (Zea mays) and lettuce (Lactuca sativa) with or without arbuscular mycorrhizal (AM) colonization by Glomus mosseae was studied in a greenhouse trial. Plant dry weights of non-AM-inoculated maize and lettuce were unaffected by the presence of A. alternata and F. equiseti. In contrast, A. alternata and F. equiseti decreased plant dry weights and mycorrhization when inoculated to the rhizosphere before G. mosseae. The saprophytic fungi inoculated 2 weeks after G. mosseae did not affect the percentage of root length colonized by the AM endophyte, but did affect its metabolic activity assessed as succinate dehydrogenase activity. Although F. equiseti inoculated at the same time as G. mosseae did not affect mycorrhization of maize roots, its effect on AM colonization of lettuce roots was similar to that with A. alternata. In the rhizosphere of both plants, the population of saprophytic fungi decreased significantly, but was not affected by the presence of G. mosseae. Our results suggest that there may have been a direct effect of the saprophytic fungi on the mycorrhizal fungi in the extramatrical phase of the latter, and when the AM fungus was established in the root the AM fungus was less affected by the saprophytic fungi.

The effect of soil phosphorus on the external mycelium growth of arbuscular mycorrhizal fungi during the early stages of mycorrhiza formation

The effects of soil P amendments and time of application on the formation of external mycelium by different arbuscular mycorrhizal (AM) fungi were studied. In the first experiment the external mycelium produced in the soil by the AM fungus Glomus etunicatum Beck. and Gerd., during the early stages of root colonization (7 and 14 days after inoculation), was quantified by the soil-agar film technique. A Brazilian Oxisol was used with three different phosphate levels, varying from deficient to supra-optimal for the plant. Significant differences were observed in the phosphate and inoculation treatments for plant dry weight, P content in the tissue, root length and root colonization, at fourteen days after planting. At 7 days, mycelium growth, root colonization and their relationship were reduced at supra-optimal P concentrations. Applications of P one week after planting reduced mycelium growth and root colonization more than when applied to the soil before planting. In a second experiment the arbuscular mycorrhizal (AM) fungi, Scutellospora heterogama (Nicol. and Gerd.) Walker and Sanders and E3 were tested and compared with Glomus etunicatum. For the species studied, the length of external hyphae per unit of colonized root length was affected by small P additions but no further significant differences were observed at high P levels. The three AM endophytes showed marked differences in their response to P in the soil: Scutellospora heterogama, although producing external mycelium more profusely than the Glomus spp., showed a higher sensitivity to soil P supply.

Response of maize to different inoculum densities of vesicular arbuscular mycorrhizal endophytes

The effect of the inoculum density of vesicular arbuscular mycorrhizal endophytes on growth and development in maize was investigated in sterilized soil under glass-house conditions. Mycorrhizal plants grew robust and produced three times more dry weight than non-mycorrhizal plants. 40 or more endophytes per plant produced the highest mycorrhizal association and the maximum growth in maize. The uninoculated plants exhibited the symptoms of chlorosis.