Plant and soil responses to mycorrhizal fungi and rhizobacteria in nodulated or nitrate-fertilized peas (Pisum sativum L.)

Rhizosphere organisms affect plant development and soil stability. This study was conducted to determine the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus [Glomus mosseae (Nicol. &>; Gerd.) Gerd. and Trappe] and a rhizobacterium (Bacillus sp.) on nitrate-fertilized or nodulated pea (Pisum sativum L.) plants and on the status of water-stable soil aggregates. The plants were grown in pots in a yellow clay-loam soil, and inoculated with the VAM fungus and the rhizobacterium, with one of the two, or with neither. The Bacillus sp. and G. mosseae did not affect shoot dry mass in nodulated plants. Under N fertilization, the VAM fungus enhanced plant growth, while the rhizobacterium inhibited shoot growth, VAM root colonization, and nodule formation, but enhanced the root:shoot and the seed:shoot ratios. The inhibition of shoot growth and of root colonization appeared to be related. The water stability and pH of the VAM soils were higher than those of the non-VAM soils. The rhizobacterium enhanced the water-stable aggregate status in the non-VAM soils only. Under both N-nutrition regimes, the soils had the greatest proportion of the water-stable aggregates when inoculated with both rhizo-organisms and the lowest when colonized by neither. The two rhizo-organisms affected both plants and soil, and these effects were modified by the source of N input through N₂ fixation or fertilization. Received: 5 April 1995     

Mycorrhizal dependency of two hawaiian endemic tree species: Koa and mamane 1

Vesicular‐arbuscular mycorrhizal (VAM) fungi have been proposed as a low‐input solution to the problem of inadequate phosphorus (P) levels in many tropical and subtropical soils. To determine the mycorrhizal dependency of two Hawaiian endemic tree species, mamane (Sophora chrysophylla Seem.) and koa (Acacia koa Gray), seedlings were grown in the greenhouse with and without the VAM fungus, Glomus aggregatum Schenck and Smith emend Koske, at three levels of soil solution P (0,0.02, and 0.20 mg P/L) in a volcanic ash soil. Inoculation significantly increased colonization of roots by the VAM fungus in both mamane and koa seedlings. At 0.02 mg P/L, mamane inoculated with the VAM fungus had significantly greater subleaflet P concentrations at 48 days after planting (DAP), and significantly greater leaf areas, shoot dry weights, and root lengths at harvest compared to uninoculated plants. At 0 mg P/L, koa grown in association with the VAM fungus had significantly greater subleaflet P concentrations at 41 DAP, and significantly greater leaf areas, and dry weights of leaves, stems, and roots at harvest. Mamane was highly dependent on the VAM association for maximum growth, while koa was moderately dependent on the VAM association. These results demonstrate that P uptake and early growth of mamane and koa can be increased significantly at low soil P levels by inoculating seedlings with an effective VAM fungus. Future research needs to demonstrate continuing positive growth benefits of VAM fungal inoculation after transplanting from the nursery to field conditions.     

Fitting plants to soil through mycorrhizal fungi: plant nutrition in host-endophyte combinations evaluated by the diagnosis and recommendation integrated system

Summary Vesicular-arbuscular mycorrhizal (VAM) fungi improve plant growth in marginal soils. This study was conducted to determine the effects of three species of VAM fungi on plant nutrition in two cultivars of corn (Zea mays L.) and one of sunflower (Helianthus annus L.). Plants were grown in pot cultures under controlled (greenhouse) conditions in a soil high in K, Mg, and P, and low in Ca and N, and were supplied with amounts of VAM-fungal inocula in which equal numbers of infective propagules had previously been determined. Analysis of variance showed highly significant main effects and interactions due to both factors (plant and fungus) for N, P, Ca, and Mg. For K, only plant effects were significant (P<0.043). The uptake of nutrients was selectively enhanced or inhibited by one or the other VAM fungus relative to non-VAM control plants. In sunflower, N concentration was markedly enhanced (73%) by the mixed inoculum of the three fungi, even though individual effects were not significant. Evaluation of leaf nutrient analyses by the Diagnosis and Recommendation Integrated System (DRIS) revealed the utility of this system to rank nutritional effects by VAM fungi in an order of relative nutrient deficiency. The DRIS therefore is seen as a useful tool in evaluating and selecting VAM fungi for the alleviation of specific nutrient disorders.Work was funded by the Program in Science and Technology Cooperation, Office of the Science Advisor, Agency for International Development, as Project No. 8.055, and was conducted in collaboration at the Colegio de Postgraduados and the Western Regional Research Center     

Effects of ammonium and nitrate on the growth of vesicular-arbuscular mycorrhizalErythrina poeppigiana O.I. Cook seedlings

Erythrina poeppigiana, a woody tropical plant, was inoculated with vesicular-arbuscular mycorrhizal (VAM) fungiGlomus etunicatum Becker and Gerdeman,G. mosseae Nicol. and Gerd. Gerdeman and Trappe, orG. intraradices Schenk and Smith. Growth, N uptake, and nutrition were evaluated in VAM-inoculated plants and controls fertilized with two levels (3 or 6 mM) of either NH _inf4 ^sup+ -N or NO _inf3 ^sup- -N. The response by the mycorrhizal plants to N fertilization, according to N source and/or level differed significantly from that of the control plants. In general, the growth of the mycorrhizal plants was similar to that of the non-mycorrhizal plants when N was provided as NH _inf4 ^sup+ . When the N source was NO _inf3 ^sup- the control plants grew significantly less than the VAM plants. Inoculation with VAM fungi gave yield increases of 255 and 268% forG. etunicatum-colonized plants, 201 and 164% forG. mosseae-colonized plants and 286 and 218% forG. intraradices-colonized plants fertilized with 3 and 6 mM NO _inf3 ^sup- -N, respectively. The increased growth and acquisition of nutrients by plants fertilized with NO _inf3 ^sup- -N and inoculated with VAM shows that VAM mycelium has a capacity for NO _inf3 ^sup- absorption. The results also showed thatE. poeppigiana seedlings preferred NH _inf4 ^sup+ as an N source.G. etunicatum was the most effective endophyte, not only increasing N, P, Ca, Mg, and Zn uptake in the presence of NO _inf3 ^sup- fertilizer but also P and Mg in the presence of NH _inf4 ^sup+ applications. From these results we conclude that VAM symbiosis affects N metabolism inE. poeppigiana plants and that this species can overcome limitations on the use of NO _inf3 ^sup- -N by the mediation of VAM fungi.     

Inoculation response in kidney beans (Phaseolus vulgaris,L.) to vesicular-arbuscular mycorrhizal fungi and rhizobia in non-sterilized soil

The effect of dual inoculation on three local cultivars (Miss Kelly, Portland Red, Round Red) of red kidney beans (Phaseolus vulgaris, L.) with four strains of Rhizobium leguminosarum bv. phaseoli and three species of vesicular-arbuscular mycorrhizal (VAM) fungi was examined in a clay loam soil. Rhizobial strains B 17 and B 36, each paired with Glomus pallidum or G. aggregatum, were the most effective pairings for cv. Miss Kelly. Inoculation of Miss Kelly with any of these pairings significantly (P=0.05) increased growth, number of nodules, nodule dry weight, mycorrhizal colonization, and shoot N and P content than other pairings. The growth response by cv. Portland Red was significantly improved by pairings of B 36 or B 17 with any of the three VAM fungi. For both cultivars (Miss Kelly and Portland Red), CIAT 652 or T 2 paired with VAM fungi did not give a positive growth response. In contrast, for cv Round Red the T 2 rhizobial strain in combination with any of the three VAM fungi showed a significant (P=0.05) growth improvement in all parameters. Our results suggest that while dual inoculation of VAM fungi and rhizobia significantly improves the growth response by red kidney beans, the best pairings of VAM fungus and rhizobia for each cultivar need to be carefully selected.     

Influence of a vesicular-arbuscular mycorrhizal fungus on the competitive ability of Bradyrhizobium spp. for nodulation of cowpea Vigna unguiculata (L.) Walp in non-sterilized soil

Summary We examined the influence of a vesicular-arbuscular (VAM) fungus (Glomus pallidum Hall) on the competitive ability of introduced and native Bradyrhizobium strains to nodulate cowpeas [Vigna unguiculata (L) Walp]. Our experiments in non-sterilized soil revealed that in the presence of VAM fungus, introduced Bradyrhizobium spp. strains become more competitive than native rhizobia. For example, strain JRC29 occupied 59.2% of the total nodules when inoculated alone, but this figure increased to 71.2% when JRC29 was used in dual inoculations with VAM fungus. A similar pattern of enhanced competitiveness for nodule formation was observed with the two other strains in the presence of the VAM fungus. Our results suggest that the competitiveness of rhizobia can be enhanced by co-inoculating with a selected strain of a VAM fungus.     

VAM Fungi Spore Populations in Different Farming Situations and Their Effect on Productivity and Nutrient Dynamics in Maize and Soybean in Himalayan Acid Alfisol

To assess the effect of five vesicular arbuscular mycorrhizae (VAM) isolates of Glomus mosseae screened out from different farming situations, two pot experiments were conducted on maize and soybean in a phosphorus (P)–deficient Himalayan acid Alfisol. There was variation in VAM spore populations of Glomus mosseae isolates screened out from maize harvested fields, soybean fields, vegetable fields, tea orchard, and citrus orchard. Glomus mosseae isolate from vegetable-based cropping system exhibited maximum root colonization at flowering in maize (32%) and soybean (28%), followed by Glomus mosseae isolate from soybean fields, and exhibited the lowest in Glomus mosseae isolate from tea farm. Glomus mosseae isolate from vegetable-dominated fields was at par with Glomus mosseae isolate from soybean-based cropping system, again resulting in significantly high root biomass, nitrogen (N)–P–potassium (K) uptake, and grain and straw productivity both in maize and soybean crops besides the greatest Rhizobium root nodule biomass in soybean. There was a considerable reduction in soil fertility with respect to NPK status over initial status in pot soils inoculated with Glomus mosseae isolate from vegetable-dominated ecosystem, thereby indicating greater nutrient dynamics by this efficient VAM strain in the plant–soil system and greater productivity in a P-deficient acidic Alfisol. Overall, VAM isolates from different cropping systems and farming situations with variable size and composition of VAM mycoflora resulted in differential effects on growth, productivity, and nutrient dynamics in field crops. Overall, Glomus mosseae isolates from vegetable and soybean fields proved to be superiormost in terms of root colonization, growth, and crop productivity as well as nutrient dynamics in above study. Thus, isolation, identification, and selection of efficient VAM strains may prove as a boon in low-input intensive agriculture in P-deficient Himalayan acidic Alfisol.     

Influence of a plant growth-promoting pseudomonad and vesicular-arbuscular mycorrhizal fungus on alfalfa and birdsfoot trefoil growth and nodulation

Summary In a growth chamber study we examined the influence of a plant growth-promoting rhizobacterium, Pseudomonas putida R-20, and an acid-tolerant vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices 25, on Medicago sativa L. and Lotus corniculatus L. growth and nodule development. Seedlings were planted in an acidic (pH 5.5), P-deficient soil containing re-established native microflora (minus VAM) and appropriate rhizobia, and inoculated with the rhizobacterium, the VAM fungus, or both. The plants were assayed at three intervals for up to 10–11 weeks. The growth-promoting rhizobacteria alone increased alfalfa shoot mass by 23% compared to all other treatments, but only at 8 weeks of growth, apparently by promoting nodulation and N₂ fixation (acetylene reduction activity). The presence of VAM, either alone or in combination with the rhizobacteria, generally decreased root length but only at 8 weeks also. As a group, the inoculation treatments increased all nodular measurements by 10 weeks of growth. Few treatment effects were found at 7 and 9 weeks for birdsfoot trefoil; neither plant nor nodular measurements differed among treatments. By 11 weeks, shoot mass was increased by the rhizobacteria alone by 36% compared to the control. As a group, the inoculation treatments all showed increased nodular responses by this time. The rhizobacteria stimulated mycorrhizal development on both plant species, but only at the initial samplings. No synergistic effects between the plant growth-promoting rhizobacterium and VAM inoculation were found. Although these results lend credence to the concept of managing microorganisms in the rhizosphere to improve plant growth, they emphasize the necessity for a more thorough understanding of microbial interactions as plants mature.     

Effects of low temperature and shade on relationships between nodulation,vesicular-arbuscular mycorrhizal infection,and shoot growth of soybeans

The effects of low temperature and reduced light on a Glycine-Bradyrhizobium-Glomus spp. symbiosis were examined in pot experiments. Soybean plants, Glycine max L. Merr. cv. Tachiyutaka, were grown with N fertilization or inoculation with Bradyrhizobium japonicum plus P fertilization or inoculation with Glomus mosseae in the glasshouse. After the flowering stage, half the pots with soybean plants were subjected to low temperature (15°C 14h/13°C 10 h) with light reduced by shading. At 0, 7, 16, and 28 days after the application of the treatments, the growth, nodulation, vesicular-arbuscular mycorrhizal (VAM) infection and the N and P contents of the soybean plants were measured. In all symbiont-fertilization combinations, the low-temperature treatment reduced the production of dry matter by the soybeans. Nodulation (weight and number) was slightly reduced by this treatment but the proportion of larger nodules was increased. The root length infected by the VAM fungus was little affected by the low-temperature treatment. Both the nodule weight and the infected root length were linearly related to shoot dry weight regardless of treatment and of the symbiont-fertilization combination used. These results suggest that the growth of the symbionts on the root was in balance with the shoot growth of the host, irrespective of climatic conditions, and imply a considerable degree of host control. P inflows to root systems were greatly affected by low-temperature treatment regardless of the symbiont-fertilization combination. This suggests that a simple comparison of P inflows between mycorrhizal and non-mycorrhizal plants may give misleading information on the effects of low temperature or reduced light conditions on P uptake by mycorrhizal plants.     

Responses of Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil

Responses of three multipurpose fruit tree species, Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam., to inoculation with five species of arbuscular mycorrhizal fungi, Acaulospora spinosa Walker and Trappe, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, Glomus intraradices Schenck and Smith, Glomus aggregatum Schenck and Smith emend. Koske and Glomus manihotis Howeler, Sieverding and Schenck, differed markedly with respect to functional compatibility. This was measured as root colonization, mycorrhizal dependence (MD) and phosphorus concentrations in shoots of plants. Root colonization of fruit trees by A. spinosa, G. aggregatum and G. manihotis was high and tree growth increased significantly as a consequence. G. intraradices also colonized well, but provided little growth benefit. G. mosseae colonized poorly and did not stimulate plant growth. The MD of P. biglobosa and T. indica was similar, reaching no more than 36%, while Z. mauritiana showed the highest MD values, reaching a maximum of 78%. The Z. mauritiana A. spinosa combination was the most responsive with respect to total biomass production; phosphorus (P) absorption probably contributed to this more than the absorption of sodium, potassium, magnesium or calcium. The density and length of root hairs were positively correlated with MD, suggesting that root hairs are not indicative of MD. Received: 20 January 1997     

Comparative Performance of Geographical Isolates of Glomus mosseae in Field Crops under Low-Input Intensive P-Deficient Acid Alfisol

Comparative performance of five geographical isolates of Glomus mosseae screened from maize fields, soybean fields, vegetable fields, tea orchard, and citrus orchard was assessed in three major field crops (wheat, maize, and soybean) under low-input management in three glass-house pot experiments in a phosphorus (P)–deficient acid Alfisol. These geographical isolates of Glomus mosseae varied with respect to vesicular arbuscular mycorrhizal (VAM) spore count and root colonization in these crops with greatest spore count (240 per 250 g soil) and root colonization (28–34%) using previously screened local Glomus mosseae culture (VAM_L) of CSK Himachal Pradesh Agricultural University, Palampur, India, followed in order by VAM isolate from vegetable-based cropping system, Glomus mosseae isolate from soybean fields, and Glomus mosseae isolate from tea farm. Glomus mosseae isolate from vegetable-based cropping system remaining at par with local VAM culture (VAM_L), resulting in significantly greatest grain productivity in these field crops under low-input management. There was a considerable reduction in soil fertility with respect to NPK status over the control and initial status in pot soils inoculated with Glomus mosseae isolate from vegetable-based cropping system followed by local VAM strain (VAM_L), thereby indicating greater nutrient mobilization and productivity as well through this efficient Glomus mosseae strain in P-deficient acid Alfisol. In addition, Glomus mosseae isolates from different farming situations resulted in differential productivity and soil fertility under these field crops. Overall, Glomus mosseae isolate from vegetable-based cropping system proved its superiority in realizing greater productivity and nutrient mobilization compared to local Glomus mosseae VAM culture under low-input management in P-deficient acid Alfisol.     

Phosphatase activity and cytokinin content in cowpeas (Vigna unguiculata) inoculated with a vesicular-arbuscular mycorrhizal fungus

We examined the effect of a vesicular-arbuscular mycorrhizal (VAM) fungus Glomus pallidum Hall on the phosphatase activity and cytokinin concentration in cowpea [Vigna unguiculata (L.) Walp] roots at successive stages of plant growth. Both acid and alkaline phosphatase activity were significantly (P=0.05) higher in mycorrhizal than in non-mycorrhizal roots 30 days after inoculation. Similarly, the cytokinin content was significantly increased in mycorrhizal roots compared to non-mycorrhizal roots. Our study suggests that these biochemical changes may improve the growth of mycorrhizal cowpea plants.     

Interactions of Glomus clarum with Acetobacter diazotrophicus in infection of sweet potato (Ipomoea batatas), sugarcane (Saccharum spp.), and sweet sorghum (Sorghum vulgare)

Summary Spores of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum obtained from sweet potatoes grown in soil inoculated with this fungus and with an enrichment culture of Acetobacter diazotrophicus contained A. diazotrophicus and several other bacteria, including a diazotrophic Klebsiella sp. Inoculation of micropropagated sweet potatoes with G. clarum and A. diazotrophicus enhanced spore formation in soil compared to VAM inoculation alone. Plants inoculated with VAM spores containing the bacteria showed additional increases in the number of spores formed within roots. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM or when present within VAM spores. Micropropagated sugarcane seedlings inoculated with the same VAM spores containing the diazotrophs also contained much higher numbers of A. diazotrophicus in aerial parts than seedlings inoculated in vitro with the bacteria alone. When grown in non-sterile soil, the sugarcane seedlings again showed the greatest infection of aerial parts after inoculation with VAM spores containing the diazotrophs. This treatment also increased VAM colonization and the numbers of spores formed within roots. Similar effects were observed in sweet sorghum except that the aerial plant parts were not infected by A. diazotrophicus.     

Manganese toxicity alleviated by mycorrhizae in soybean

Abstract

Soybean (Glycine max (L.) Merr.) plants nodulated with Bradyrhizobium japonicum. Nitragin strain 61A118, were grown with or without the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. Gerd.) Gerd. and Trappe in pot cultures in soil high (40.4 μg/g) in available Mn. Leaves of the nonVAM plants showed severe symptoms of Mn toxicity and had toxic (314 μg/g) concentrations of Mn in the foliage. NonVAM plants had significantly lower dry weights and nodule mass than VAM plants. Concentrations of Mn in the VAM plants were significantly (P<0.05) lower than in the nonVAM plants, and there were no symptoms of Mn toxicity. Both VAM and nonVAM plants had a significant negative correlation between shoot dry mass and leaf Mn concentration. Since levels of Mn increased with increasing VAM‐fungal colonization, we conclude that it was not the VAM condition per se which alleviated Mn toxicity. We suggest that the significantly higher levels of Mn in the leaves (P<0.05) and the roots (P<0.001) of nonVAM plants was due to increased uptake of Mn by the nonVAM plants. This exudation, which are generally observed in nonVAM plants, and to the role of such exudates in solubilizing MnO₂ and chelating the resulting Mn²? for facilitated absorption.     

Synergistic effects of vesicular-arbuscular mycorrhizal fungi and diazotrophic bacteria on nutrition and growth of sweet potato (Ipomoea batatas)

Summary Sweet potatoes were micropropagated and then transplanted from axnic conditions to fumigated soil in pots in the greenhouse. Spores of Glomus clarum were obtained from Brachiaria decumbens or from sweet potatoes grown in soil infected with this fungus and with an enrichment culture of Acetobacter diazotrophicus. Three experiments were carried out to measure the beneficial effects of vesicular-arbuscular mycorrhizal (VAM) fungi-diazotroph interactions on growth, nutrition, and infection of sweet potato by A. diazotrophicus and other diazotrophs obtained from sweet potato roots. In two of these experiments the soils had been mixed with ¹⁵N-containing organic matter. The greatest effects of mycorrhizal inoculation were observed with co-inoculation of A. diazotrophicus and/or mixed cultures of diazotrophs containing A. diazotrophicus and Klebsiella sp. The tuber production was dependent on mycorrhization, and total N and P accumulation were increased when diazotrophs and G. clarum were applied together with VAM fungal spores. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM fungi or when present within G. clarum spores. More pronounced effects on root colonization and intraradical sporulation of G. clarum were observed when A. diazotrophicus was co-inoculated. In non-fumigated soil, dual inoculation effects, however, were of lower magnitude. ¹⁵N analysis of the aerial parts and roots and tubers at the early growth stage (70 days) showed no statistical differences between treatments except for the VAM+Klebsiella sp. treatment. This indicates that the effects of A. diazotrophicus and other diazotrophs on sweet potato growth were caused by enhanced mycorrhization and, consequently, a more efficient assimilation of nutrients from the soil than by N₂ fixation. The possible interactions between these effects are discussed.     

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.     

Influence of inoculation with bradyrhizobium japonicum and glomus claroideum on seed yield of soybean under greenhouse and field conditions

Soybean plants [Glycine max (L.) Men., cv. Polanka], inoculated with the VAM fungus Glomus claroideum Schenck and Smith and Bradyrhizobium japonicum strain D344, were grown in pots and in the field. The VAM fungus positively influenced N2 fixation, nodulation and N, P, K, and Mg concentrations in the leaves. In pots, (at green pods formation) VAM inoculated plants produced a 24% greater biomass as compared with non‐inoculated plants colonized by native VAM populations. Under field conditions characterized by a high level of P and N, the seed yield of VAM inoculated plants increased in comparison with non‐ and only rhizobia‐inoculated soybean (+28% and 17%, respectively). Glomus claroideum was capable of competing with the native VAM populations both in the greenhouse and in the field experiment.     

Lime‐chlorosis occurrence and leaf mineral composition of grapevine treated by root microorganisms

One‐year‐old rooted cuttings of Vitis vinifera L. cv. Pinot blanc clone 55, grafted on “S.O.4” and “41 B” hybrid rootstocks, were grown in pots containing a calcareous soil. Before potting, the roots were infected by the VAM fungus (Glomus mosseae) and by a suspension of the following endophytic bacteria: Erwinia sp., Pseudomonas fluorescens, Enterobacter cloacae. The shoot growth was checked every ten days and leaf blade chlorophyll and mineral elements were assayed at the middle of the annual growing cycle as well as the mineral composition of the leaf petiole. Chlorosis was rated by visual screening as well in order to control the effect of the root treatments on the chlorosis occurrence. The most significant findings of the trial were: a) root infection with Erwinia sp. and Pseudomonas fluorescens increased the chlorophyll concentration over the untreated plants in both the graft combinations, b) the plants grafted on “S.O.4” rootstock did benefit from the treatment with Glomus mosseae as well, and c) root infection with Enterobacter cloacae depressed growth and chlorophyll concentration in both the graft combinations.     

Influence of humic acids on laurel growth,associated rhizospheric microorganisms,and mycorrhizal fungi

Summary Increasing concentrations of humic acids were tested in order to determine their effects on the microbial rhizosphere and the growth of laurel (Laurus nobilis L.). Plants that were treated with 300 mg kg^-1 of humic acids had the heaviest weights of both fresh and dry shoots; however, doses of 3000 mg kg^-1 were highly phytotoxic and inhibited the growth of laurel. Total aerobic bacteria and actinomycetes were stimulated by doses of 1500 and 3000 mg kg^-1 of humic acids at the first harvest. Nevertheless, at the end of the experiment no significant differences were found among the different doses. The number of fungi living in the laurel rhizosphere was not affected by any concentration of humic acids. Vesicular-arbuscular mycorrhizal (VAM) colonization was only slightly affected by the addition of increasing concentrations of humic substances to the soil, while the hyphal growth of Glomus mosseae was reduced.     

Influence of bacteria on growth and phosphorus nutrition of mycorrhizal corn

Com plants were grown in a non‐sterile soil in a greenhouse or in hydroponic culture in a growth chamber. We studied the influence of chitinolytic, pectinolytic, P‐solubilizing bacterial isolates, and a collection of bacterial strains on the development of native vesicular‐arbuscular mycorrhizal (VAM) populations, colonization of roots by the VAM fungus Glomus fasciculatum and their influence on the phosphorus (P) nutrition and growth of plants. As compared with VAM native control, the most potent stimulants for root colonization of soil‐grown plants by the VAM native population was a strain of Agrobacterium radiobacter and isolate H30. All bacteria used significantly supressed shoot fresh weight of mycorrhizal plants (‐13% up to ‐37%), with the exception of Agrobacterium. Under hydroponic conditions, the P‐solubilizing isolate F27 significantly stimulated the intensity of mycorrhiza, the number of arbuscules in roots, and increased both the P concentration and P content in corn shoots (+30% and +35%), than did the VAM fungus alone. Isolate F27 significantly increased shoot dry weight as compared with the mycorrhizal control. The other bacteria did not influence biomass production of corn.