Nodulation and N,-fixation of groundnut were investigated in sole and intercropping systems.Intercropping with pearl millet, maize, or sorghum reduced nodulation and N 2 -fixation. This effect is ascribed to the shading of groundnut by the cereal component and the consequent decrease in photosynthesis of the legume canopy.

This paper tries to illustrate how beneficial interactions between crops can be exploited to increase the overall output of a cropping system. Growth studies with sorghum/pigeonpea and millet/groundnut are described to show how intercropping systems can achieve much larger yields than sole crops by using environmental resources more fully over time or more efficiently in space. Data from moisture stress studies are presented to illustrate that these advantages of intercropping can be even greater under stress conditions.

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A laccase produced by Pleurotus ostreatus MTCC 142 under solid-state fermentation using co-substrates of paddy straw and corn husk (1.5:1.5, g w/w) showed an activity of 2.54 U gds−1. Laccase activity was determined spectrophotometrically using 0.5 mM 2,2′- azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS). Supplementation with fructose and potassium nitrate resulted in maximum enzyme production at initial pH 5.8 ± 0.2 and initial moisture content of 70%. A carbon: nitrogen ratio of 0.5:0.1 yielded highest laccase activity in the presence of surfactant Tween 20 (0.05%, w/v). Incorporation of vanillin (5 mM) and copper sulphate (10 mM) facilitated enhanced synthesis of laccase. A 4.8-fold increase in enzyme activity was recorded after optimization of nutritional parameters. The apparent molecular mass of this enzyme was revealed as 43 kDa by sodium dodecyl sulphate–polyacrylamide gel electrophoresis. The laccase showed optimal activity at pH 3 and 35 °C with 82.8% residual activity after 1 h of incubation. The Km and Vmax values on ABTS were found to be 0.52 mM and 9.33 U gds−1, respectively. The enzyme activity was enhanced by Cu2+ and remained unaffected with Ba2+, Mn2+, Pb2+, Mg2+, Ca2+ and Fe3+. However, pre-incubation of the enzyme with reagents like sodium azide, sodium lauryl sulphate and 2-mercaptoethanol demonstrated an inhibition of its activity. Addition of crude laccase to Congo red dye solution resulted in 36.84% decolourization after 20 h of incubation at 35 ± 2 °C. This study discusses the production and characterization of a laccase from P. ostreatus strain with potential for azo dye decolourization.

Random transposon TnS mutagenesis of Bradyrhizobium sp. (Arachis) strain NC92, a member of the cowpea cross-inoculation group, was carried out, and kanamycin-resistant transconjugants were tested for their symbiotic phenotype on three host plants: groundnut, siratro, and pigeonpea. Two nodulation (Nodphenotype) mutants were isolated. One is unable to nodulate all three hosts and appears to contain an insertion in one of the common nodulation genes (nodABCD); the other is a host-specific nodulation mutant that fails to nodulate pigeonpea, elicits uninvaded nodules on siratro, and elicits normal, nitrogen-fixing nodules on groundnut. In addition, nine mutants defective in nitrogen fixation (Fix-phenotype) were isolated. Three fail to supply symbiotically fixed nitrogen to all three host plants. Surprisingly, nodules elicited by one of these mutants exhibit high levels of acetylene reduction activity, demonstrating the presence of the enzyme nitrogenase. Three more mutants have partially effective phenotypes (Fix') in symbiosis with all three host plants. The remaining three mutants fail to supply fixed nitrogen to one of the host plants tested while remaining partially or fully effective on the other two hosts; two of these mutants are Fix-in pigeonpea and Fix' on groundnut and on siratro, whereas the other one is Fix-on groundnut but Fix' on siratro and on pigeonpea. These latter mutants also retain significant nodule acetylene reduction activity, even in the ineffective symbioses. Such bacterial host-specific fixation (Hsf) mutants have not previously been reported.Specific strains of rhizobia enter into nitrogen-fixing symbioses with specific host plants, almost exclusively legumes. Successful recognition between compatible bacterial and plant partners elicits the development of a novel plant organ, the root nodule. The bacteria invade the developing nodule and there differentiate into the nitrogen-fixing "bacteroid" form (reviewed in references 21 and 73).There are two major groups of rhizobia, commonly known as the fast-and the slow-growing species. These two groups differ by many biochemical and physiological criteria and have recently been placed in two separate genera, Rhizobium and Bradyrhizobium, respectively (36). The two groups also differ in several symbiotic properties. For example, Bradyrhizobium strains can be induced to fix nitrogen in free-living culture (42, 47, 54), whereas Rhizobium species will only fix nitrogen symbiotically; fast-growing species generally infect only a few, closely related legumes, whereas Bradyrhizobium species of the cowpea cross-inoculation group can infect a broad range of diverse legume hosts (25); fast-growing species almost invariably infect their hosts via the root hairs, whereas a single slow-growing species may infect one host, such as pigeonpea, by the root hairs, and another, such as groundnut, by direct intercellular penetration between the epidermal cells-so-called crack entry (17,21,37).Significant progress has been made in the identification of bacterial gen...