The structure of N2-fixing nodules of faba bean (Vicia faba L.) was investigated by means of light and electron microscopy to determine possible pathways for metabolite movement. The central infected zone is enclosed by a cortex, which is composed of a loosely arranged outer part and a densely packed inner part. Both are separated by the nodule endodermis, which borders on the root endodermis and continuously envelopes the entire nodule interior, with the exception of the apical meristematic region. Vascular bundles, located peripherally within the inner cortex, are surrounded by another endodermal layer. Radial cell walls of both nodule and vascular endodermis are incrusted and form Casparian bands. Additionally, all endodermal cells are coated by suberin lamellae. These modifications may prevent an apoplastic loss of solutes from the enclosed tissues, and require a symplastic metabolite passage. This is supported by high plasmodesmatal frequencies found between vascular endodermis and inner cortex. Within vascular bundles, transfer cells adjacent to xylem elements may play a role in xylem loading. The central infected tissue contains uninfected cells, possibly representing a symplastic continuity. These cells may form a preferred metabolite pathway since plasmodesmata are extremely sparse between infected cells. The low number of uninfected cells in the central tissue of V faba nodules favors an additional apoplastic pathway.

The organophosphorus insecticide Selecron [O-(4-bromo-2-chlorophenyl) O-ethyl S-n-propyl-phosphorotioate] at 10 and 50 ppm significantly decreased respiration, mycelial protein, extracellular protein and mycelial dry weight of Aspergillus fumigatus, A. terreus and Myceliophthora thermophila when grown at 45°C. Cx and C1 cellulases of tested fungi were significantly decreased. However, C1 cellulase of A. fumigatus was slightly increased.

Of 13 Rhizobium and Bradyrhizobium strains investigated for the production of cellular and extracellular phosphodiesterase and phosphotriesterase, all were found to produce both enzymes. Phosphodiesterase was produced at a much higher level than phosphotriesterase. Rhizobium meliloti TAL 1373 was the most productive. The extracellular enzymes were activated by inclusion in the assay mixture of Ca2+ or Mg2+. The enzymes were inhibited by Zn2+ but not significantly affected by Cu2+, Co2+ and Mn2+. Both hydrolases were inhibited by dithiothreitol but not by thiol-directed inhibitors, suggesting that sulphydryl groups are not directly involved in catalysis. The enzymes have the ability to hydrolyse some organophosphorus compounds, suggesting that Rhizobium and Bradyrhizobium strains play an important role in the degradation of organophosphorus pesticides.

Seeds of faba bean (Vicia faba L.) cultivar Giza 3 were screened for the presence of mycotoxins. Eleven out of 100 samples were positive. Aflatoxins B1 and B2 were found in 7 samples with a mean concentration of 30 μg kg−1 seeds. Aflatoxins B1 B2, G1 and G2 and ochratoxin A were each detected twice in separate samples with a mean concentration of 25 and 20 μg kg−1, respectively. Mycotoxins at concentrations of 100 or 200 μg kg−1 soil significantly decreased nodule number, nodule fresh weight and total nitrogenase activity. This was translated into reductions in dry matter accumulation and nitrogen yield of the bean. Mycotoxins also suppressed specific nitrogenase activity, NADH-dependent glutamate dehydrogenase (NADH-GDH) as well as glutamate synthase (NADH-GOGAT) activities. In addition, mycotoxins inhibited synthesis of leghaemoglobin, carbohydrate and protein in the nodule cytosol. Of the mycotoxins tested, aflatoxin B1 was the most toxic. The decline in nitorgenase activity and total N concentration in the plants could be attributed to mycotoxins interfering with normal nodule physiology and function.

Azotobacter chroococcum was isolated from straw-amended soil and found to utilize 4-hydroxybenzoic acid, resorcinol, pyrocatechol and vanillic acid as sole carbon source. Growth and nitrogenase activity ofA. chroococcum were supported by 8, 6 and 4 mmol/L of 4-hydroxybenzoic acid, resorcinol and pyrocatechol, respectively. The generation time of 1.71 h in 4-hydroxybenzoic acid did not significantly differ from the generation time of 1.64 h, observed when grown in mannitol. 4-Hydroxybenzoic acid was utilized rapidly. However, the decomposition of other tested phenolic compounds set in only slowly. It was concluded that this isolate has good potential to utilize some phenolic compounds released during biodegradation of plant wastes.

In soil salinized with different concentrations of sodium chloride, the total counts of soil fungi were significantly decreased during 11 weeks of incubation. Similarly, the total count of bacteria and actinomycetes were severely depressed by increasing salinity level above 5%. Invertase and urease activities were severely decreased as NaCl concentration increase during the incubation. Also, the effect on nitrate reductase was inhibitory with most treatments.

Six strains and a commercial inoculant of Bradyrhizobium japonicum were evaluated in association with Glycine max (L.) cultivar Clark. Inoculated and uninoculated plants were grown in pot and field experiments. Nodules were counted and weighed and roots and shoots were separated and analysed for total nitrogen. In pot experiments, two of six bacterial strains were superior to the other four, and to the commercial inoculant (Nitragin) in promoting greater root and top growth and plant nitrogen accumulation. In the field experiment, there were indications that environmental conditions may have affected nodulation by the bacteria. The strains could be divided into three groups according to nodule efficiencies, accumulation of plant dry matter, and total nitrogen content. The greater variations in nodule efficiencies of the tested strains could be attributed to the quantities of bacteroid, cytosol protein and leghaemoglobin in the nodules.

The effect of four bacterial and six fungal species on nodulation and growth ofVicia faba cv. Giza 3 inoculated withRhizobium leguminosarum biovarviceae strain RCR 1001 were assessed in a pot experiment.Bacillus cereus, Pseudomonas fluorescens, Aspergillus niger andA. quadriliniatus either alive cells or sterile filtrate significantly promoted nodulation, growth and nitrogen accumulation. Heat-killed cells had no effect. --------------------------------------------------------------------------------

Coculturing of eight rhizobial strains (Bradyrhizobium japonicum USDA 110, USDA 3447, RCR 3407, RCR 3442, Rhizobium meliloti TAL 1372, TAL 1373, R. leguminosarum biovar viceae RCR 1001, and RCR 1044) and five rock-phosphate-solubilizing fungi (Aspergillus egyptiacus, A. flavus, A. niger, A. ochraceus, and Penicillium citrinum) was tested on yeast extract-mannitol agar. B. japonicum strains USDA 110, USDA 3447, RCR 3442, R. leguminosarum biovar viceae RCR 1001, and RCR 1044 grew successfully in cocultures with the tested fungal species in yeast extract-mannitol agar without antagonism. Among these fungi, A. niger showed the highest potentialities to solubilize rock- phosphate at all incubation temperatures examined (15, 28, 38, and 42°C), and phosphate dissolution maximized at 28°C. Survival of Rhizobium/Bradyrhizobium strains and the best rock-phosphate-solubilizing fungus (A. niger) was evaluated monthly in four carrier materials (Peat, wheat bran, sugarcane baggase, and wheat straw) at 28 and 38°C. The number of colony-forming units recovered on agar plates for all cocultured microorganisms was the highest with peat as a carrier, followed by bran and sugarcane baggase. On the other hand, survival of cocultured microorganisms strongly reduced in wheat straw. Survival of all microorganisms was the best at 28°C. Cocultures of B. japonicum USDA 3447/A. niger and R. leguminosarum RCR 1044/A. niger were the more tolerant for storage conditions whereas the number of colony-forming units in cocultures of B. japonicum USDA 110/A. niger and R. leguminosarum RCR 1001/A. niger was strongly reduced. Peat or bran inoculants of R. leguminosarum RCR 1044/A. niger and B. japonicum USDA 3447/A. niger significantly increased dry matter yield, nitrogen (N) and phosphorus (P) contents of faba bean and soybean, respectively, when grown in alkaline soil amended with rock-phosphate

Abstract: The present study was made to isolate and assess some physiological characteristics of root nodule-colonizing fungi. During this study, 17 fungal species were isolated from root nodule samples taken from faba bean plants (Vicia faba L.) collected from different sites at Assiut area (Egypt). The growth of faba bean plants in pots was significantly promoted by soil inoculation with most fungi. Growth was checked in pots with inocula of Cladosporium cladosporioides, Fusarium moniliforme, F: oxysporium, F solani, Macrophominia phaseolina and Rhizoctonia solani which were added separately. All growth-promoting fungi were capable of producing cellulase, pectin lyase, polygalacturonase, protease, urease, amidase, acid phosphatase, alkaline phosphatase and arylsulfatase in growth medium supplemented with the corresponding substrates. Four fungal species, Aspergillus awamori, A. flavus, Penicillium chrysogenum and Trichoderma koningii showed the highest rates of enzyme formation. The effect of the addition of six trace elements to the growth media at 30 micromol/ml on enzyme production revealed some dependency on species, enzyme and metal ion. Cd2+, Hg2+ and Zn2+ generally inhibited enzyme activity. Cu(1+), Fe3+ and Al3+ showed a stimulatory effect. Fungicides (afugan and tilt) and herbicides (brominal and fusilade) at 50 ppm generally promoted enzyme activity, but insecticides (kelthane and fenvalerate) caused some inhibition to enzyme activities. Salinization of the growth media with NaCl strongly inhibited the enzymatic activity of all fungi at concentrations between 0.5 and 1.5%