The response of white clover to different strains ofRhizobium trifolii in hill land reseeding: A second trial
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Trifolium repens
Crop Productivity
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Many factors that contribute to alfalfa's excellence, but recognition must be given to the microsymbiont, the nodule bacteria that fix free nitrogen from the atmosphere. Early studies of the rhizobia:legume association revealed that there were many kinds of nodule bacteria and that various leguminous plants had their preference. Biochemical studies on N fixation in legume root nodules have been made with the soybean because it is an easy plant to culture, shows a marked response to effective rhizobia, and yields abundant nodule tissue. The principles elucidated are applicable to alfalfa and other nodulating leguminous plants. The number of rhizobia required for effective nodulation under any particular set of conditions depends greatly upon the type of inoculum employed. Inoculation is not considered necessary on the high-Ca soils of the West but is strongly recommended on the more acid soils of the Northwest USA.
Nodule (geology)
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During the spring of both 1968 and 1969 three phalaris-white clover pasture types, differing in botanical composition from clover-dominant to grass-dominant, were grazed by beef cattle. The cattle were scored twice a day for bloat incidence and severity and were weighed each month. No cattle died from bloat or any other cause. Of the 289 moderate and severe cases of bloat observed during the experiment, 221 occurred on the high clover pasture type (60-80 per cent white clover) ; comparable figures on the medium clover (30-50 per cent white clover) and low clover (15-25 per cent white clover) pasture types were 58 and 10 respectively. In addition to the greater incidence of bloat, liveweight gains on the highest clover pasture were 20-30 per cent lower than on the the other two pasture types in both years. The digestibility and availability of the herbage on the clover-dominant pasture equalled or exceeded that of pastures containing <50 per cent white clover ; reduced liveweight gains were attributed to a depressive effect of bloat on herbage intake.
Trifolium repens
Drought Tolerance
Beef Cattle
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Dry weight
Germ plasm
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Abstract Three glasshouse trials investigated N2fixation in white clover following inoculation with rhizobia from caucasian clover. We grew white clover in agar, vermiculite/perlite and soils low in available‐N and with no detectable rhizobia. Media were subsequently treated with inoculum containing rhizobia effective on either (i) caucasian clover, (ii) white clover, or (iii) mixtures of the two. The percentage of ineffective nodules on white clover increased as the proportion of rhizobia from caucasian clover in the inoculant mix increased. However, the percentages of ineffective nodules on white clover were less than the proportion of ineffective rhizobia in the inoculant, indicating that the ineffective rhizobia were less competitive in nodule formation. Foliage yield and symbiotic N2fixation in white clover were not significantly affected when ineffective rhizobia from caucasian clover made up 67% or less of the inoculant. However, when ineffective rhizobia made up a high proportion of the inoculant mix (>92%), both foliage yield and N2 fixation were significantly reduced compared with plants inoculated with only white clover rhizobia. Extrapolation of the present glasshouse results to the field is difficult and further field trials are required to determine if rhizobia from caucasian clover have any effect on symbiotic N2fixation of white clover in pastoral situations.
Trifolium repens
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Bradyrhizobium japonicum
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When nitrogen is limited, many legume plants form beneficial associations with nitrogen-fixing rhizobia. Efficient reduction of atmospheric nitrogen by rhizobial nitrogenase is restricted to plant nodules, inside which rhizobia establish persistent colonies of intracellular bacteroids. Of all known nodulating rhizobia, Sinorhizobium fredii strain NGR234 fixes nitrogen with >130 legumes. Genetic basis for such symbiotic promiscuity was linked to a 536 kb plasmid called pNGR234a. In this study, we aimed at downsizing pNGR234a to a core of essential loci sufficient to sustain proficient interactions with legumes. Hence, synthetic plasmids carrying loci needed for the flavonoid-dependent synthesis of basic nodulation factor structures (pMiniSym2) and functions required for nitrogen fixation (pMiniSym4) were constructed. When mobilized into a derivative of NGR234 cured of pNGR234a or into non-symbiotic soil bacteria, pMiniSym2 conferred nodulation and infection abilities to recipient strains. However, pMiniSym4 failed to confer a robust SNF, suggesting additional work is needed to secure SNF.
Sinorhizobium meliloti
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Nitrogen Cycle
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Bradyrhizobium
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In biological nitrogen fixing (BNF), symbiosis Rhizobium infects the root of leguminous plants. The potential of this symbiosis is its specificity for Rhizobium strains. To assess the success of BNF in the agricultural area of Western Azarbaijan, Iran, the nitrogen fixation potential of the Iranian native inoculators Rhizobium strains isolated from root nodules of clover from western and eastern Azarbaijan were compared with two imported Australian strains (TAl and WU95). Nitrogen fixation capacity was measured for two cultivars of clover, Trifolium alexandrium (Karaj and Winterpass). The effectiveness of TAl was significantly higher than the WU95 and native strains. The imported and native strains of rhizobia significantly differed with respect to the two clover cultivars. The time required for nodulation was influenced by strains of rhizobia. Nodules were first visible 14 days after inoculation by TAl, but they required 17 and 19 days for clover inoculated by native and WU95 strains, respectively. There was no difference between the two native strains. The result obtained may provide a basis for agricultural exploitation of N2 fixation in Iran.
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