Symbiosis of Trifolium subterraneum with mycorrhizal fungi and Rhizobium trifolii as affected by ammonium sulphate and nitrification inhibitors

The symbioses between Trifolium subterraneum, mycorrhizal fungi and Rhizohium are affected by (NH₄)₂SO₄ and by the nitrification inhibitors 2-chloro-6 (trichloromethyl) pyridine (N-Serve) and 2-trichloromethyl pyridine (2TMP). At 50 μg · g^?1 soil N-Serve and 2TMP had toxic effects on plant growth, measured as leaf expansion, root length and dry weight. Lower concentrations of N-Serve also produced some toxic symptoms. The addition of (NH₄)₂SO₄ to the soil at 2 and 6 m-equiv NH⁺₄ per pot, resulted in reduced root length and nodulation. Shoot dry weight was reduced at 6 m-equiv NH⁺₄ per pot. In the presence of (NH₄)₂SO₄ the toxic effects of the nitrification inhibitors on plant growth were less.Both nitrification inhibitors reduced development of mycorrhizal entry-points and extent of root colonization (% infection). Percentage infection of the root system was also reduced by (NH₄)₂SO₄. Development of nodules on the lateral roots was increased in the presence of N-Serve at 5 and 15 μ · g^?1. This effect, however, was accompanied by a marked reduction in N₂ase activity. Smaller increases in nodulation were apparent with 2TMP and were associated with variable N₂ase activity.     

Competition between species of Rhizobium for nodulation of Glycine max

Glycine max cv. Malayan is a promiscuously nodulating cultivar which formed nodules with 6 out of 9 strains of Rhizobium spp of diverse origin and all strains of R. japonicum tested. No generalizations can be made as to the probability of strains isolated from a particular host being infective on Malayan as only some isolated from Centrosema pubescens, and Cajanus cajan were able to form nodules. In competition with R. japonicum at 30°C all 20 strains of Rhizobium spp isolated from Malayan grown in Nigeria formed fewer than 50% of the nodules and 14 strains fewer than 25%. Competition was influenced by root temperature. Three strains of Rhizobium spp were poor competitors with R. japonicum between 24° and 33°C but at 36°C they formed more nodules (74–88%) than R. japonicum. Another strain of Rhizobium spp formed the majority of the nodules between 27° and 36°C whereas R. japonicum formed the most at 24°C.     

Nodule distribution on legume roots: Specificity and response to the presence of soil

Roots of siratro, cowpea, and two cultivars of soybean were inoculated with either Rhizobium sp. 3G4b16 or R. fredii 191. The numbers and distribution of nodules were determined after hydroponic growth of the plants for 10 days in plastic growth pouches. The uppermost nodules on the primary roots of both siratro and cowpea were clustered near the position occupied by the root tip at the time of inoculation. This is the region thought to be maximally susceptible to nodulation. Appreciable numbers of nodules also were scattered down the length of the primary root. Nodulation of McCall and Vicoja soybean (in growth pouches) was very different to that in an autoclaved greenhouse soil mixture. Strain × cultivar-specific differences in the numbers of nodules on primary roots were obliterated by soil. Soil reduced the extent of scattering of nodules along primary roots and shifted the ratios of primary root nodules to lateral root nodules. Soil also caused a 95% reduction in the number of McCall root hairs infected by strain 3G4b16. The soil environment appears to obliterate strain × cultivar-specific variation that is expressed when inoculated plants are grown hydroponically in growth pouches.     

Oil shale process water affects activity of vesicular-arbuscular fungi and rhizobium 4 years after application to soil

The effects of different concentrations of water from oil shale processing on the vesicular-arbuscular (VA) fungal and Rhizobium activity of an arid land soil were investigated 4 yr after contamination. Effects were assessed in field plots and by a greenhouse bioassay. Addition of process water had marked effects on the chemistry of the soil and increased concentrations of Ca, Mg, Na, NO₃ and NH₄ as well as raising the electrical conductivity. VA infection analysis of roots from field plots and the bioassay combined with counts of VA fungal spores indicate reduced mycorrhizal activity in treated soils. The individual species of VA fungi were found to be affected differently by the process water. Roots of the legume yellow sweetclover developed fewer nodules in soils treated with retort water. An acetylene reduction assay indicated that nitrogenase activity was reduced in nodules from soils treated with undiluted process water.     

Depth of root symbiont occurrence in soil

Summary The woody legume Prosopis glandulosa (mesquite) growing in the California Sonoran Desert develops functional root symbiotic associations (N₂-fixing nodules, vesicular-arbuscular mycorrhizal fungi) at depths greater than 4 m in moist soil above a seasonally stable water table. Population densities of symbiotic microorganisms are substantially greater at depth than near the surface. Inferences of plant symbiotic dependence based upon examination of surface roots and soil may be incorrect since deep roots can support the symbioses which are critical for plants utilizing deep water.     

Improved zinc tolerance in Eucalyptus globulus inoculated with Glomus deserticola and Trametes versicolor or Coriolopsis rigida

The potential of interactions between saprophytic and arbuscular mycorrhizal (AM) fungi to improve Eucalyptus globulus grown in soil contaminated with Zn were investigated. The presence of 100 mg kg ⁻¹ Zn decreased the shoot and root dry weight of E. globulus colonized with Glomus deserticola less than in plants not colonized with AM. Zn also decreased the extent of root length colonization by AM and the AM fungus metabolic activity, measured as succinate dehydrogenase (SDH) activity of the fungal mycelium inside the E. globulus root. The saprophytic fungi Trametes versicolor and Coriolopsis rigida increased the shoot dry weight and the tolerance of E. globulus to Zn when these plants were AM-colonized. Both saprophytic fungi increased the percentage of AM root length colonization and elevated G. deserticola SDH activity in the presence of all Zn concentrations applied to the soil. In the presence of 500 and 1000 mg kg⁻¹ Zn, there were higher metal concentrations in roots and shoots of AM than in non-AM plants; furthermore, both saprophytic fungi increased Zn uptake by E. globulus colonized by G. deserticola. The higher root to shoot metal ratio observed in mycorrhizal E. globulus plants indicates that G. deserticola enhanced Zn uptake and accumulation in the root system, playing a filtering/sequestering role in the presence of Zn. However, saprophytic fungi did not increase the root to shoot Zn ratio in mycorrhizal E. globulus plants. The effect of the saprophytic fungi on the tolerance and the accumulation of Zn in E. globulus was mediated by its effect on the colonization and metabolic activity of the AM fungi.     

Hyperparasitism of oospores of Phytophthora megasperma var. sojae

Hyperparasites of oospores of Phytophthora megasperma Drechs. var. sojae Hildb. were present in each of 15 field soils tested. Maximum numbers of oospores parasitized ranged from 42.5 to 87.5% for flooded soils, and from 25.5 to 73.0% for soils adjusted to 50% water holding capacity; the mean for all soils was 51.5%. The frequency of hyperparasitism was not correlated with the disease potential soils for Phytophthora root-rot of soybean as determined in seedling tests on flooded soil samples. Of eight isolated hyperparasitic fungi tested in steamed soil, the most efficient parasites were Hyphochytrium catenoides, Humicola fuscoatra, and Pythium monospermum, each of which parasitized at least 76% of oospores during 3 weeks. Hyphae were not parasitized by any of the eight fungi. Parasitism by H. catenoides in sterilized soil increased as soil temperature increased from 16° to 28°C. Parasitism by P. monospermum was maximum at 20°–24°C. Oospores of P. meyasperma var. sojae race 7 were more resistant to infection by hyperparasites than were oospores of races 1 and 3. Oospores produced in culture were slightly more susceptible to hyperparasitism in soils than were oospores produced in soybean seedlings.     

The bacterial community of tomato rhizosphere is modified by inoculation with arbuscular mycorrhizal fungi but unaffected by soil enrichment with mycorrhizal root exudates or inoculation with Phytophthora nicotianae

Arbuscular mycorrhizal (AM) fungi have been shown to induce the biocontrol of soilborne diseases, to change the composition of root exudates and to modify the bacterial community structure of the rhizosphere, leading to the formation of the mycorrhizosphere. Tomato plants were grown in a compartmentalized soil system and were either submitted to direct mycorrhizal colonization or to enrichment of the soil with exudates collected from mycorrhizal tomato plants, with the corresponding negative controls. Three weeks after planting, the plants were inoculated or not with the soilborne pathogen Phytophthora nicotianae growing through a membrane from an adjacent infected compartment. At harvest, a PCR-Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments amplified from the total DNA extracted from each plant rhizosphere was performed. Root colonization with the AM fungi Glomus intraradices or Glomus mosseae induced significant changes in the bacterial community structure of tomato rhizosphere, compared to non-mycorrhizal plants, while enrichment with root exudates collected from mycorrhizal or non-mycorrhizal plants had no effect. Our results support that the effect of AM fungi on rhizosphere bacteria would not be mediated by compounds present in root exudates of mycorrhizal plants but rather by physical or chemical factors associated with the mycelium, volatiles and/or root surface bound substrates. Moreover, infection of mycorrhizal or non-mycorrhizal plants with P. nicotianae did not significantly affect the bacterial community structure suggesting that rhizosphere bacteria would be less sensitive to the pathogen invasion than to mycorrhizal colonization. Of 96 unique sequences detected in the tomato rhizosphere, eight were specific to mycorrhizal fungi, including two Pseudomonas, a Bacillus simplex, an Herbaspirilium and an Acidobacterium. One Verrucomicrobium was common to rhizospheres of mycorrhizal plants and of plants watered with mycorrhizal root exudates.     

Accumulation of specific flavonoids in soybean (Glycine max (L.) Merr.) as a function of the early tripartite symbiosis with arbuscular mycorrhizal fungi and Bradyrhizobium japonicum (Kirchner) Jordan

This study is the first report assessing the effect of soil inoculation on the signalling interaction of Bradyrhizobium japonicum, arbuscular mycorrhizal fungi (AMF) and soybean plants throughout the early stages of colonisation that lead to the tripartite symbiosis. In a study using soil disturbance to produce contrasting indigenous AMF treatments, the flavonoids daidzein, genistein and coumestrol were identified as possible signals for regulating the establishment of the tripartite symbiosis. However, it was unclear whether soil disturbance induced changes in flavonoid root accumulation other than through changing the potential for AMF colonization. In this study, soil treatments comprising all possible combinations of AMF and B. japonicum were established to test whether (1) modifications in root flavonoid accumulation depend on the potential for AMF colonization, and (2) synthesis and accumulation of flavonoids in the roots change over time as a function of the early plant-microbial interactions that lead to the tripartite symbiosis. The study was comprised of two phases. First, maize was grown over 3-week periods to promote the development of the AM fungus Glomus clarum. Second, the interaction between soybean, G. clarum and B. japonicum was evaluated at 6, 10, 14 and 40 days after plant emergence. Root colonization by G. clarum had a positive effect on nodulation 14 days after emergence, producing, 30% more nodules which were 40% heavier than those on roots solely inoculated with B. japonicum. The tripartite symbiosis resulted in 23% more N₂ being fixed than did the simpler symbiosis between soybean and B. japonicum. The presence of both symbionts changed accumulation of flavonoids in roots. Daidzein and coumestrol increased with plant growth. However, development of the tripartite symbiosis caused a decrease in coumestrol; accumulation of daidzein, the most abundant flavonoid, was reduced in the presence of AMF.     

Abundance of arbuscular mycorrhizal fungi in relation to soil salinity around Lake Urmia in northern Iran analyzed by use of lipid biomarkers and microscopy

Saline soils around Lake Urmia in northern Iran constitute a stressed environment for plants and microbial communities, including arbuscular mycorrhizal (AM) fungi. Soil and root samples were collected from fields cultivated with the glycophytes Allium cepa L. and Medicago sativa L., and sites dominated by the halophyte Salicornia europaea L. Soil and root samples were analyzed for the AM fungal signature neutral lipid fatty acid (NLFA) 16:1ω5. The roots were also examined microscopically for mycorrhizal colonization. Each plant species was sampled across a salt gradient. Microscopic examination showed no AM fungal structures in the roots of S. europaea. The highest root colonization was recorded for M. sativa. The highest NLFA 16:1ω5 values were found in soil around M. sativa roots and the lowest in soil around S. europaea roots. We found evidence for stimulation of vesicle formation at moderate salinity levels in M. sativa, which is an indication of increased carbon allocation to mycorrhiza. On the other hand, we found a negative correlation between salinity and arbuscule formation in A. cepa, which may indicate a less functional symbiosis in saline soils.     

Influence of Glomus etunicatum/Zea mays mycorrhiza on atrazine degradation, soil phosphatase and dehydrogenase activities, and soil microbial community structure

The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37 μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0 mg kg⁻¹. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0 mg kg⁻¹, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure.     

Fraxinus-Glomus-Pisolithus symbiosis: Plant growth and soil aggregation effects

It has been established that arbuscular mycorrhizal (AM) fungi are involved in the conservation of soil structure. However, the effect of ectomycorrhizal (EM) fungi alone or in interaction with AM fungi in soil structure has been much less studied. This experiment evaluated EM and AM fungi effects on soil aggregation and plant growth. Ash plants (Fraxinus uhdei) were grown in pots, and were inoculated with Glomus intraradices and Pisolithus tinctorius separately but also in combination. Our results showed that F. uhdei established a symbiotic association with EM and AM fungi, and that these organisms, when interacting, showed synergistic and additive effects on plant growth compared to singly inoculated treatments. EM and AM fungi prompted changes in root morphology and increased water-stable aggregates. AM fungi affect mainly small-sized macroaggregates, while EM and EM-AM fungi interaction mainly affected aggregates bigger than 0.5 mm diameter. These results suggest that ectomyccorrhizal as well as arbuscular mycorrhizal fungi should be considered in restoration programs with Fraxinus plants.     

Bacillus subtilis NRRL B‐30408 inoculation enhances the symbiotic efficiency of Lens esculenta Moench at a Himalayan location

Field‐based experiments were conducted to evaluate the promotion abilities of Bacillus subtilis NRRL B‐30408 for growth of lentil (Lens esculenta Moench) at a mountain location of Indian Himalaya in two consecutive years. Observations were recorded for plant growth, yield, nodulation, root colonization by arbuscular mycorrhizal and endophytic fungi, and other related parameters. A positive influence of bacterial inoculation on plant biomass and yield‐related parameters was recorded in both years. The significant increase in growth and nodule numbers as well as leghaemoglobin and protein concentrations of nodules indicated an enhancement in efficiency of the Rhizobium–legume symbiosis due to bacterial inoculation. An increase in protein concentration was also recorded for shoots, leaves, and seeds. Due to bacterial inoculation, there was an increase in colonization by endophytic fungi and a simultaneous decrease in colonization by arbuscular mycorrhizal fungi in roots. Based on the results of this field study, inoculation with suitable plant growth–promoting rhizobacteria instead of dual inoculation is suggested as a better option for improving the yield and related attributes of a primary dietary legume such as lentil.     

Collembola effects on plant mass and nitrogen acquisition by ash seedlings (Fraxinus pennsylvanica)

We studied the effects of varied collembolan numbers on three compensatory mechanisms of nutrient uptake: fine root mass, endomycorrhizal development, and physiological uptake capacity. We grew ash (Fraxinus pennsylvanica) with or without the arbuscular mycorrhizal fungus Glomusintraradices, with 0, 10 or 50 initial Collembola (Folsomia candida). After 83 d root and uptake rates, endomycorrhizal development, and plant biomass were determined. Plant mass increased with Collembola number. Collembola interacted with mycorrhizae in their effects on N uptake and leaf N. Collembola in the absence of mycorrhizal roots were associated with lower N uptake and leaf N at 10 than at 0 or 50 initial Collembola. In contrast, Collembola in the presence of mycorrhizal roots were associated with the highest rate of N uptake and leaf N at 10 versus 0 or 50 initial Collembola. Hence as initial Collembola number increased, the relative importance of root system traits that determined N uptake changed from root physiological uptake capacity, presence of mycorrhizal roots, to fine root biomass.     

Changes in soil aggregation and glomalin-related soil protein content as affected by the arbuscular mycorrhizal fungal species Glomus mosseae and Glomus intraradices

Arbuscular mycorrhizal (AM) fungi are key organisms of the soil/plant system, influencing soil fertility and plant nutrition, and contributing to soil aggregation and soil structure stability by the combined action of extraradical hyphae and of an insoluble, hydrophobic proteinaceous substance named glomalin-related soil protein (GRSP). Since the GRSP extraction procedures have recently revealed problems related to co-extracting substances, the relationship between GRSP and AM fungi still remains to be verified. In this work the hypothesis that GRSP concentration is positively correlated with the occurrence of AM fungi was tested by using Medicago sativa plants inoculated with different isolates of Glomus mosseae and Glomus intraradices in a microcosm experiment. Our results show that (i) mycorrhizal establishment produced an increase in GRSP concentration - compared to initial values - in contrast with non-mycorrhizal plants, which did not produce any change; (ii) aggregate stability, evaluated as mean weight diameter (MWD) of macroaggregates of 1-2 mm diameter, was significantly higher in mycorrhizal soils compared to non-mycorrhizal soil; (iii) GRSP concentration and soil aggregate stability were positively correlated with mycorrhizal root volume and weakly correlated with total root volume; (iv) MWD values of soil aggregates were positively correlated with values of total hyphal length and hyphal density of the AM fungi utilized.The different ability of AM fungal isolates to affect GRSP concentration and to form extensive and dense mycelial networks, which may directly affect soil aggregates stability by hyphal enmeshment of soil particles, suggests the possibility of selecting the most efficient isolates to be utilized for soil quality improvement and land restoration programs.     

Hyphal translocation and uptake of sulfur by vesicular-arbuscular mycorrhizae of onion

Translocation of S by external hyphae of Glomus fascieulatus, a vesicular-arbuscular (VA) mycorrhizal fungus, was demonstrated. When tracers were injected 8 cm from onion roots in soil chambers, both ³⁵S and ³²P appeared in roots of mycorrhizal plants. Neither radionuclide was present in non-mycorrhizal plants.In a second soil-chamber experiment, mycorrhizal onions took up more ³⁵S per unit dry weight than non-mycorrhizal controls when ³⁵S was injected into soil chambers in a region 3–6 cm from roots. Severing of external hyphae between the application area and the roots reduced the concentration of ³⁵S in tops of mycorrhizal plants but not in roots. Volatile ³⁵S per unit dry weight collected from all plants in each treatment was highest in the mycorrhizal-hyphae intact treatment, and higher in the mycorrhizal-hyphae severed treatment than the non-mycorrhizal treatment. Movement of ³⁵S in soil from the area of application to roots was similar for all treatments.Increased uptake of S from soil by VA mycorrhizal plants can result from hyphal translocation of S to infected roots by external mycorrhizal hyphae.     

Dual inoculation of pretransplant stage Oryza sativa L. plants with indigenous vesicular-arbuscular mycorrhizal fungi and fluorescent Pseudomonas spp.

Summary This study examined the response of rice (Oryza sativa L.) plants at the pretransplant/nursery stage to inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi and fluorescent Pseudomonas spp., singly or in combination. The VAM fungi and fluorescent Pseudomonas spp. were isolated from the rhizosphere of rice plants. In the plants grown in soil inoculated with fluorescent Pseudomonas spp. alone, I found increases in shoot growth, and in root length and fine roots, and decreases in root growth, and P and N concentrations. In contrast, in the plants colonized by VAM fungi alone, the results were the reverse of those of the pseudomonad treatment. Dual inoculation of soil with VAM fungi and fluorescent Pseudomonas spp. yielded plants with the highest biomass and nutrient acquisition. In contrast, the plants of the control treatment had the lowest biomass and nutrient levels. The dual-inoculated plants had intermediate root and specific root lengths. The precentages of mycorrhizal colonization and colonized root lengths were significantly lower in the dual-inoculated treatment than the VAM fungal treatment. Inoculation of plants with fluorescent Pseudomonas spp. suppressed VAM fungal colonization and apparently reduced photosynthate loss to the mycorrhizal associates, which led to greater biomass and nutrient levels in dual-inoculated plants compared with plants inoculated with VAM fungi alone. Dual inoculation of seedlings with fluorescent Pseudomonas spp. and VAM fungi may be preferable to inoculation with VAM alone and may contribute to the successful establishment of these plants in the field.     

The uptake and translocation of phosphate by mycelial strands of pine mycorrhizas

Uptake and rapid translocation of ³²P-orthophosphate to Pinus radiata mycorrhizas from soil by mycelial strands of Rhizopogon luteolus was demonstrated. In greenhouse material, translocation occurred from soil for at least 12 mm and some 30–80 per cent of phosphate absorbed from 5 × 10^?6M as KH₂PO₄ was translocated. In the field, translocation occurred for 12 cm. Uptake by excised mycelial strands was metabolically mediated. Translocation occurred more rapidly when the untreated ends of strands were placed in an osmoticum: polarity in translocation was also observed. It was concluded that uptake and translocation by mycelial strands (as distinct from individual hyphae) provide an effective method for mycorrhizal exploitation of large inter-root soil volumes and assist the plants in competition for nutrients.Large differences occurred between strains of the same species in mycelial strand growth in soil. Mycelial strands of R. luteolus grew through the test soil at 1.3-2.9 mm/day and along P. radiata roots at 1.7 mm/day at 25°C day and 16°C night temperatures.     

Biostatic effect of fumigation and pesticide drenches on an endomycorrhizal-Rhizobium-legume tripartite association under field conditions

The effects of formaldehyde fumigation and pesticide drenching with Bavistin, Cuman, Copperthom, Sulfex, Furadon, and Termix at recommended rates on vesicular-arbuscular mycorrhizal (VAM) colonisation and Rhizobium sp. nodules were assessed regularly for a period of 90 days in the legumes Cajanus cajan, Dolichos biflorus, Vigna mungo, and V. unguiculata under field conditions. The fumigant and the pesticides initially reduced VAM fungal colonisation and the number of spores in all plants. Following the initial decrease there was a slow recovery, but by 90 days after emergence, root colonisation was either parallel to or still lower than the control, and the number of spores was still well below control levels for all species except C. cajan, which had more VAM spores than the control in all treatments except fumigation and Furadon. Although the number of nodules did not differ from control levels at 30 days after emergence, differences were evident during the later stages of plant growth for all species except V. unguiculata. The effect of pesticides on VAM fungi and root nodulation varied with the associated host plant species. Plant tissue P and VAM colonisation were significantly correlated in all host plants. The pesticide treatments had no marked effect on plant growth, but accumulations of nutrients in pesticide-treated plants were lower than those in untreated plants. Growth and nutrient status of the legumes varied with VAM fungal colonisation.     

Hydrolytic enzyme activities in maize (Zea mays) and sorghum (Sorghum bicolor) roots inoculated with Gluconacetobacter diazotrophicus and Glomus intraradices

Two strains of Gluconacetobacter diazotrophicus (Pal 5, UAP5541) and the arbuscular mycorrhizal fungus Glomus intraradices increased both the shoot and root dry weight of sorghum 45 days after inoculation, whereas they had no effect on the shoot and root dry weight of maize. Co-inoculation (Gluconacetobacter diazotrophicus plus Glomus mosseae) did not increase the shoot and root dry weight of either plant. There was a synergistic effect of Gluconacetobacter diazotrophicus on root colonization of maize by Glomus intraradices, whereas an antagonistic interaction was observed in the sorghum root where the number of Gluconacetobacter diazotrophicus and the colonization by Glomus intraradices were reduced. Plant roots inoculated with Gluconacetobacter diazotrophicus and Glomus intraradices, either separately or together, significantly increased root endoglucanase, endopolymethylgalacturonase and endoxyloglucanase activities. The increase varied according to the plant. For example, in comparison with non-inoculated plants, there were higher endoglucanase (+328%), endopolymethylgalacturonase (+180%) and endoxyloglucanase (+125%) activities in 45-day old co-inoculated maize, but not in 45-day old sorghum. The possibility is discussed that hydrolytic enzyme activities were increased as a result of inoculation with Gluconacetobacter diazotrophicus, considering this to be one of the mechanisms by which these bacteria may increase root colonization by AM fungi.