Sulfonylurea residues have been found to inhibit the growth of some legume crops and pastures in seasons following application. Negative effects of these herbicides on symbiotic nitrogen fixation by legume crops and pastures have been demonstrated. Reductions in nitrogen fixation may result from a direct effect of the herbicide on rhizobial growth and/or an indirect effect on plant growth. In this study the influence of chlorsulfuron on the growth of chickpea rhizobia [Mesorhizobium ciceri (CC1192)], the growth of chickpea plants, and the extent of nodulation and nitrogen fixation by the chickpea/rhizobia symbiosis were examined. In vitro studies (in yeast mannitol broth and a defined medium) showed that chlorsulfuron applied at double the recommended field application rate did not influence the growth of chickpea rhizobia. An experiment using 14C-labelled chlorsulfuron was conducted to determine if rhizobial cells exposed to chlorsulfuron could deliver the herbicide to the point of root infection and nodule formation. Approximately 1% of the herbicide present in the rhizobial growth medium remained with the cell/inoculum material after rinsing with 1/4 strength Ringer’s solution. This was considered unlikely to affect chickpea growth, nodulation, or nitrogen fixation. A pot experiment was used to define the influence of chlorsulfuron on the growth, nodulation, and nitrogen fixation of chickpeas. The presence of chlorsulfuron in the soil reduced the nodulation and nitrogen fixation of the chickpea plants. Pre-exposing rhizobia to chlorsulfuron before inoculating them into pots with germinating chickpea seeds, reduced the number of nodules formed by 51%. Exposure of chickpeas and chickpea rhizobia to chlorsulfuron can adversely affect the formation and activity of symbiotic nitrogen-fixing nodules, even when only the rhizobial inoculant is exposed briefly to the herbicide.

Influence of chlorsulfuron on rhizobial growth, nodule formation, and nitrogen fixation with chickpea

It is documented that majority of soils in Africa have low levels of nitrogen and phosphorous and hence the capability to support plant growth such as leguminous crops is limited. The supply of these mineral nutrients is vital in enhancing legume growth and development. The potential role(s) of nitrogen from rhizobial inoculants and phosphorous in legumes growth with respect to growth, yield, economic benefits, photosynthesis and plant nutrition is given special attention in this review.

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Possible benefits of rhizobial inoculation and phosphorus supplementation on nutrition, growth and economic sustainability in grain legumes

The influence of inorganic N on the development of mycorrhizal symbiosis inLeucaena leucocephala(Lam.) de Wit was studied in an Oxisol subjected to simulated erosion. The plants were grown in pots containing soil samples inoculated with the VAM fungusGlomus aqgregatumand amended with 0, 25, 50 or 100 ppm N. The extent of VAM colonization of roots increased with increasing levels of N in both eroded and uneroded soils. However, the level of infection was significantly higher in the eroded soil than in the uneroded one. Mycorrhizal activity monitored in terms of P content of leucaena subleaflets increased significantly in the eroded soil when it was amended with 25 ppm N and became similar to that observed in the uneroded soil. Nodule dry matter production and shoot N concentration increased significantly with N application upto 50 ppm. Above this level of N, nodule dry weight declined while N concentration did not change. Application of 25 ppm N to the eroded soil also significantly increased shoo...

Influence of inorganic N on mycorrhizal activity, nodulation, and growth ofLeucaena leucocephalain an oxisol subjected to simulated erosion

In order to quickly and efficiently evaluate the salt tolerance of alfalfa, salinity tests were conducted on Medicago sativa L. var. australis, var. icon, var. loi, and var. gea, under in vitro conditions. Pregerminated seeds of four varieties were subjected to five different NaCl concentrations (0, 50, 100, 150, 200 mM). The influence of saline stress was estimated on the basis of survival percentage, growth parameters, and electrolyte leakage. The seedlings surviving on the medium enriched with salt at the highest concentration were presumed to be tolerant and represented the mother plants for the production of in vitro clones. In the following step, the clones were evaluated in vitro to confirm the salt tolerance. The influence of mild salt stress (75 mM NaCl) on the growth parameters of selected clones was examined. At the end of this trial, the proline accumulation and sodium content in alfalfa shoots were also quantified. The results suggest an increased level of proline promotes salt tolerance. Medicago sativa L. var. icon is highly tolerant in comparison with the other varieties tested. In vitro selection of M. sativa L. varieties on salt-containing media allowed us to obtain clones with increased salinity tolerance.

https://www.tpbin.com/Uploads/Subjects/3324dd0f-a9b3-48de-b68a-7c94b69f3d59.pdf

Alfalfa (Medicago sativa L.) clones tolerant to salt stress: in vitro selection

Zn deficiency is widespread in traditional areas of chickpea cultivation worldwide. It limits chickpea productivity and causes significant losses to the economies of the world?s largest chickpea exporters. This review may be of interest to researchers who would like to contribute to the improvement of chickpea cultivation on Zn-depleted soils in an environmentally sustainable manner, namely via identification of genotypes with superior symbiotic performance under Zn-limited conditions. The primary aim of the current work is to familiarize the readers with the biology and symbiotic characteristics of chickpea, and also to provide the necessary background on Zn as an essential nutrient for symbiotic nitrogen fixation (SNF). Special attention has been paid to the choice of rhizobial strains compatible with chickpea. Strains that can serve as an inoculum for simultaneous analysis of many genetically diverse chickpea lines have been suggested. The genotypes listed in this work can be good starting material for identification of chickpea lineages useful for unraveling the molecular basis of Zn-use efficiency, SNF efficiency, or both.

/pdf/zn-use-efficiency-for-optimization-of-symbiotic-nitrogen-1m81ze6c08.pdf

Zn-use efficiency for optimization of symbiotic nitrogen fixation in chickpea (Cicer arietinum L.)

A controlled environment experiment was used to examine the growth and nodulation response of chickpea to a range of soil nitrate (NO
 3
 −
 ) levels (0, 0.75, 1.5, 3.0, 6.0 mM). Dry matter production, nodule mass and number, dinitrogen (N2) fixation via the acetylene (C2H2) reduction method, total nitrogen content and NO
 3
 −
 concentration were measured at 56 and 90 days from inoculated and uninoculated plants. It was found that chickpeas were less sensitive to the inhibitory effects of NO
 3
 −
 than soybeans. High NO
 3
 −
 appeared to inhibit the production of nodules early in growth, however, by the second harvest nodulation was stimulated by high NO
 3
 −
 levels. Increasing NO
 3
 −
 levels gave positive responses in tops and roots dry weight production but, proportionally, these effects were greatest with uninoculated plants. 3 and 6 mM NO
 3
 −
 gave similar root and tops dry weight in inoculated plants after 90 days. Nodule dry weight production per pot was maximised at 3.0 mM NO
 3
 −
 at both plant harvests. Whilst NO
 3
 −
 at 6 mM still gave a strong stimulation of acetylene reduction compared to 0 and 0.75 mM NO
 3
 −
 , there appeared to be a trend suggesting an inhibitory effect of 6 mM NO
 3
 −
 on C2H2 reduction compared to 1.5 and 3.0 mM NO
 3
 −
 .

Sandra J. Hetherington

Papers

The effect of soil nitrate on the growth, nodulation and nitrogen fixation of chickpeas (Cicer arietinum)