Mohamed Hemida Abd-Alla

Use of organic phosphorus byRhizobium leguminosarum biovarviceae phosphatases

Rhizobium leguminosarum biovarviceae strain TAL 1236 growing on different organic P compounds as sources of phosphate exhibited phosphatase activities. The strain was able to produce both acid and alkaline phosphatase. However, its ability to produce alkaline phosphatase was much higher. When cellular phosphate fell to 0.115% of cell protein, cellular and extracellular phosphatase activities were enhanced. Mg2+, Co2+, and Ca2+ stimulated the activity of alkaline phosphatase more than acid phosphatase. However, Mn2+ and Fe2+ activated acid phosphatase rather than alkaline phosphatase. It may be concluded thatR. leguminosarum contributes significantly to the release of P from organic compounds through the action of phosphatase which can be activated by a range of cations.

The impact of pesticides on arbuscular mycorrhizal and nitrogen-fixing symbioses in legumes

Effects of the pesticides Afugan, Brominal, Gramoxone, Selecron and Sumi Oil on growth, nodulation and root colonisation by arbuscular mycrrhizal (AM) fungi of the legumes cowpea (Vigna sinensis L.), common bean (Phaseolus vulgarisL.) and Lupin (Lupinus albus L.) were determined. The growth of all plants was inhibited by pesticide application, but this effect varied with the pesticide and plant species. Nodule formation was significantly inhibited in cowpea after 20 days of planting by all pesticides tested. Following the initial decrease, there was recovery from the inhibitory effects at 40 and 60 days after planting. Although the number of nodules on common bean and lupin did not differ from control at 20 days after planting, differences were evident during the later stages of plant growth. The pesticides significantly inhibited AM root colonisation and the number of spores in all legumes, but on the other hand, spore formation was stimulated in pesticide-treated cowpea 60 days after planting. The accumulation of N, P and K in pesticide-treated plants was lower than in control plants. Growth and nutrient status of the legumes varied with nodulation and AM colonisation. The results suggest that pesticides affect plant growth, Rhizobium/Bradyrhizobium and AM fungi at different stages of plant growth and effects varied with pesticide and plant species.

Phosphatases and the utilization of organic phosphorus by Rhizobium leguminosarum biovar viceae

Rhizobium leguminosarum biovar viceae strain TAL 1236 growing on different organic phosphorus compounds as sources of phosphate exhibited phosphatase activities. The strain was able to produce both acid and alkaline phosphatases. However, its ability to produce alkaline phosphatase was much higher. When cellular phosphate fell to 0.115% of cell protein, cellular and extracellular phosphatase activities were promoted. Mg2+, Co2+ and Ca2+ enhanced slightly the activity of alkaline phosphatase more than acid phosphatase. However, Mn2+ and Fe2+ activated acid phosphatase rather than alkaline phosphatase. It may be concluded that Rh. leguminosarum plays an important role in the release of phosphorus from its organic compounds through the action of phosphatases which can be slightly activated by a range of cations.

Growth and Enzyme Activities of Fungi and Bacteria in Soil Salinized with Sodium Chloride

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.

Synergistic interaction of Rhizobium leguminosarum bv. viciae and arbuscular mycorrhizal fungi as a plant growth promoting biofertilizers for faba bean (Vicia faba L.) in alkaline soil

Egyptian soils are generally characterized by slightly alkaline to alkaline pH values (7.5-8.7) which are mainly due to its dry environment. In arid and semi-arid regions, salts are less concentrated and sodium dominates in carbonate and bicarbonate forms, which enhance the formation of alkaline soils. Alkaline soils have fertility problems due to poor physical properties which adversely affect the growth and the yield of crops. Therefore, this study was devoted to investigating the synergistic interaction of Rhizobium and arbuscular mycorrhizal fungi for improving growth of faba bean grown in alkaline soil. A total of 20 rhizobial isolates and 4 species of arbuscular mycorrhizal fungi (AMF) were isolated. The rhizobial isolates were investigated for their ability to grow under alkaline stress. Out of 20 isolates 3 isolates were selected as tolerant isolates. These 3 rhizobial isolates were identified on the bases of the sequences of the gene encoding 16S rRNA and designated as Rhizobium sp. Egypt 16 (HM622137), Rhizobium sp. Egypt 27 (HM622138) and Rhizobium leguminosarum bv. viciae STDF-Egypt 19 (HM587713). The best alkaline tolerant was R. leguminosarum bv. viciae STDF-Egypt 19 (HM587713). The effect of R. leguminosarum bv. viciae STDF-Egypt 19 and mixture of AMF (Acaulospora laevis, Glomus geosporum, Glomus mosseae and Scutellospora armeniaca) both individually and in combination on nodulation, nitrogen fixation and growth of Vicia faba under alkalinity stress were assessed. A significant increase over control in number and mass of nodules, nitrogenase activity, leghaemoglobin content of nodule, mycorrhizal colonization, dry mass of root and shoot was recorded in dual inoculated plants than plants with individual inoculation. The enhancement of nitrogen fixation of faba bean could be attributed to AMF facilitating the mobilization of certain elements such as P, Fe, K and other minerals that involve in synthesis of nitrogenase and leghaemoglobin. Thus it is clear that the dual inoculation with Rhizobium and AMF biofertilizer is more effective for promoting growth of faba bean grown in alkaline soils than the individual treatment, reflecting the existence of synergistic relationships among the inoculants.

SURVIVAL OF RHIZOBIA/BRADYRHIZOBIA AND A ROCK-PHOSPHATE-SOLUBILIZING FUNGUS ASPERGILLUS NIGER ON VARIOUS CARRIERS FROM SOME AGRO-INDUSTRIAL WASTES AND THEIR EFFECTS ON NODULATION AND GROWTH OF FABA BEAN AND SOYBEAN

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.

Solubilization of rock phosphates byRhizobium andBradyrhizobium

The ability ofRhizobium andBradyrhizobium strains to solubilize phosphate from hydroxyapatite was determined in a medium containing NH4Cl or KNO3. The presence of NH4+ in the medium resulted in higher solubilization of phosphate as compared to the presence of KNO3, with the exception ofR. leguminosarium bv. viceae strain TAL 1236 and 1402 which solubilized comparable amounts of phosphate in a medium containing either KNO3 or NH4Cl. These results suggest that the strains employ two different mechanisms for phosphate solubilization, one depending on the presence of NH4+, the other not requiring its presence. Temperature and aeration (O2 demand) optima were 30°C and 4.2 Hz (shaking frequency), respectively. In nonsterile soil the tested strain (R. meliloti TAL 1236) was very effective in solubilizing rock phosphate.

Physiological aspects of fungi isolated from root nodules of faba bean (Vicia faba L.)

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%.

Root-hair infection and nodulation of four grain legumes as affected by the form and the application time of nitrogen fertilizer

The effects of application of combined nitrogen fertilizer (ammonium nitrate or urea) on root-hair infection and nodulation of four grain legumes were studied. Young roots of each legume were inoculated with their compatible rhizobia. The application of the two forms of combined N either at the early stages of plant growth and/or at the time of nodule formation depressed root-hair curling, infection and nodulation. Infection of hairs on the primary roots was more sensitive to the N fertilizer than hair infection of secondary roots in bothVicia faba andPisum sativum. The nodule number and total fresh mass of the four legumes were drastically affected by fertilizer application. The combined N added both at early and at later stages significantly reduced the nodulation ofV. faba, Phaseolus vulgaris andVigna sinensis. The inhibitory effect of urea on nodulation ofP. sativum was only observed when the fertilizer was applied at the late stages of plant growth. It is concluded that, although the nodulation of the four legumes was suppressed by combined N, the initial events ofRhizobium-legume symbiosis (infection of roots and nodule initiation) are more sensitive to combined N than the stages after nodule formation.

Functional structure of the indeterminate Vicia faba L. root nodule: implications for metabolite transport

Summary The structure of N 2 -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.