Response of groundnut (Arachis hypogaea L) to Rhizobium inoculation in the field: Problems and prospects

A successfulRhizobium inoculant strain needs to be more competitive than native soil rhizobia in forming nodules and to be effective in fixing nitrogen. Persistence of the strain from one season to the next will be an added advantage, since it eliminates the need to inoculate every season. Earlier studies indicated that groundnut,Arachis hypogaea, seldom responds toRhizobium inoculation in soils already containing rhizobia which nodulate groundnut. However, the results of seven years of research at ICRISAT have opened up the prospect of inoculating groundnut in such soils. These experiments indicate that inoculating with sufficient numbers of an effectiveRhizobium strain, NC 92, applied as a liquid slurry below the seed, increased yields of certain groundnut cultivars. Similar results were reported from other research centres in India. Inoculation with NC 92 for two consecutive seasons increased the proportion of nodules formed by this strain, from 25–32% in the first season to 41–54% in the second season, indicating that this strain can persist in the field for the following season. This paper also discusses results of experiments relating to host cultivar specificity and some possible problems in applying this information to farmers' fields. Strain NC 92 also produces a siderophore, an iron chelating compound, which may help in the iron nutrition of the plan

Nitrogen Nutrition of Groundnut in Alfisols

This bulletin covers aspects of demand and acquisition of nitrogen by groundnut (Arachis hypogaea). Results of experiments conducted in Alfisols at ICRISAT Center to improve groundnut productivity with Bradyrhizobiutn inoculation and fertilizer-N, together with those relating to host cultivar specificity, and some possible problems in applying this information to farmers' fields are discussed. Although it is possible to increase N2 f ixat ion through plant breeding, it is suggested that breeding for increased N2 fixation is not a practical proposition

Community-linked maternal death review (CLMDR) to measure and prevent maternal mortality: a pilot study in rural Malawi.

In Malawi, maternal mortality remains high. Existing maternal death reviews fail to adequately review most deaths, or capture those that occur outside the health system. We assessed the value of community involvement to improve capture and response to community maternal deaths

Factors Influencing Nitrogenase Activity (Acetylene Reduction) by Root Nodules of Groundnut, Arachis hypogaea L.

Acetylene reduction assay, used to measure nitrogenase activity of legume root nodules, is influenced by environmental factors, which limit its application. The effects of some of the environmental factors on acetylene reduction by groundnut root nodules are described. The activity was nonlinear during the first hour of incubation. Assay temperature above 25 C decreased the activity. Washing the nodulated roots prior to the assay also decreased the activity. The activity was influenced by light intensity, soil moisture, and moisture content in the incubation bottle. Diurnal fluctuation with one maximum and one minimum activity period during a 24 hour cycle was observed. Nitrogenase activity was higher during the postrainy season compared to that of the rainy season. A virginia cultivar Kadiri-71 had higher nitrogenase activity than a dwarf valencia cultivar, MH 2

Studies on nitrogen fixation by groundnut at ICRISAT

Symbiotic nitrogen fixation depends on an interaction between the Rhizobium strain, host plant genome and environment. We are examining all the three components with the objective of increasing biological nitrogen fixation by groundnut........

Enumeration of rhizobia by enzyme-linked immunosorbent assay (ELISA)

The use of the enzyme-linked immunosorbent assay (ELISA) to enumerate rhizobia in peat carrier and in soil has been investigated. The ELISA technique takes less time than the conventional plant infection technique often used to enumerate rhizobia present in the presence of other micro-organisms. A minimum of 102–103 cells are required for a detectable ELISA reaction, limiting the use of this technique when the number of rhizobia is low

Detection and assay of siderophores in cowpea rhizobia (Bradyrhizobium) using radioactive Fe (59Fe)

In this paper we describe a method for the detection and assay of siderophore (catechol type) using radioactive 59Fe. Using this method we have found that cowpea rhizobia (Bradyrhizobium) differ in their ability to produce this type of siderophore

Effect of manganese toxicity on growth and N2 fixation in groundnut, Arachis hypogaea

The development of manganese (Mn) toxicity symptoms and its effects on the growth, nodulation, and nitrogen fixation of groundnut genotypes were examined using a quartz-sand/solution culture system. The 11 genotypes tested all accumulated considerable concentrations of manganese (1.04–3.07 mg g-1dry matter) when supplied with 15 μg Mn ml-1of nutrient solution daily. Toxicity symptoms differed between genotypes: some showed no visual effects, some produced marginal leaf spots, and others developed marginal leaf spots coupled with an inward rolling of the margins of the younger leaves. The growth of one genotype (ICG 5394) grown with inorganic nitrogen as its source of N was more severely affected by Mn toxicity than when dependent on symbiotic fixation for its nitrogen

Competition among strains of bradyrhizobium and vesicular-arbuscular mycorrhizae for groundnut (Arachis hypogaea L.) root infection and their effect on plant growth and yield

Strains of Bradyrhizobium influenced root colonization of groundnuts by a species of vesicular-arbuscular mycorrhizae (VAM), and species of VAM influenced root nodulation by strains of Bradyrhizobium in pot experiments. In a field experiment, the effects of VAM on competition amongst inoculated bradyrhizobia were less evident, but inoculation with Bradyrhizobium strains increased root colonization by VAM. Certain VAM/Bradyrhizobium inoculum strain combinations produced higher nodule numbers. Plants grown without Bradyrhizobium and VAM but supplied with ammonium nitrate (300 micro g/ml) and potassium phosphate (16 micro g/ml) produced higher DM yields than those inoculated with both symbionts in the pot experiment. Inoculation with either symbiont in the field did not result in higher pod and haulm yields at harves