Relationships between rhizobial diversity and host legume nodulation and nitrogen fixation in tropical ecosystems
Bala, A. ; Giller, K.E. - \ 2006
Nutrient Cycling in Agroecosystems 76 (2006)2-3. - ISSN 1385-1314 - p. 319 - 330.
genetic diversity - symbiotic specificity - vigna-unguiculata - zimbabwean soils - kenyan soils - populations - bradyrhizobium - competition - nodules - beans
With recent advances in rhizobial phylogeny, questions are being asked as to how an ecological framework can be developed so that rhizobial classification and diversity could have greater practical applications in enhancing agricultural productivity in tropical ecosystems. Using the results of studies on tropical rhizobia which nodulate agroforestry tree legumes, three ecological aspects of rhizobial biodiversity were used to illustrate how its potential can be exploited. The results showed that legumes nodulate with diverse rhizobial types, thus contributing to the success of legumes in colonising a wide range of environments. There was an apparent shift in the relative dominance of rhizobia populations by different rhizobial types as soil pH changed. The Rhizobium tropici-type rhizobia were predominant under acidic conditions, Mesorhizobium spp. at intermediate pH and Sinorhizobium spp. under alkaline conditions. The R. tropici-type rhizobia were the most effective symbiotic group on all the host legumes. However, strains of Sinorhizobium spp. were as effective as the R. tropici types in N2-fixation on Gliricidia sepium, Calliandra calothyrsus and Leucaena leucocephala; while Mesorhizobium strains were equally as effective as the R. tropici types on Sesbania sesban. Classification of rhizobia based on phenotypic properties showed a broad correlation with groupings based on 16S rRNA sequence analysis, although a few variant strains nested with the dominant groups in most of the clusters. Some of the phenotypic characters that differentiated different rhizobial groups are highlighted and a case is made for the need to standardise this method
Genetic diversity of rhizobia associated with common bean (Phaseolus vulgaris L.) grown under no-tillage and conventional systems in Southern Brazil
Kaschuk, G. ; Hungria, M. ; Andrade, D.S. ; Campo, R.J. - \ 2006
Applied Soil Ecology 32 (2006)2. - ISSN 0929-1393 - p. 210 - 220.
polymerase-chain-reaction - symbiotic nitrogen-fixation - management-systems - microbial biomass - soil - strains - nodulation - populations - host - bradyrhizobium
Brazil is the largest producer and consumer of the common bean (Phaseolus vulgaris L.), but yields are often low and may be improved by a higher N supply through symbiosis with rhizobia. One main limitation to the N2-fixation process is the susceptibility of the symbiosis to environmental stresses frequent in the tropics, such as high soil temperatures and low soil moisture contents. Among other benefits, the no-tillage (NT) system reduces those stresses resulting in higher N2 fixation rates and yields; however, the effects of NT on rhizobial diversity are poorly understood. This study evaluated the diversity of rhizobia compatible with common bean in cropping areas under the NT or the conventional tillage (CT) systems in Ponta Grossa, State of Paraná, Southern Brazil. Genetic diversity was assessed by DNA analyses using the methodologies of BOX-PCR and RFLP-PCR of the 16S rDNA region. A high level of diversity was observed among the strains and the DNA profiles from the CT system were quite different from those from the NT system. Twenty-three RFLP-PCR profiles were obtained, indicating that many tropical rhizobial species remain to be described. Strain differentiation was achieved in the BOX-PCR analysis; diversity was slightly higher under the NT when compared with the CT system. Surprisingly, the rhizobial grouping based on cluster analysis of the RFLP-PCR of the 16S rDNA region indicated a higher diversity of species under the CT. It could be that the environmental stability offered by the NT system has led to a decrease in the number of species, with the predominance of the most successful ones, although genetic diversity within each species has increased. The results obtained in this study show that we still understand poorly the relation between microbial diversity and soil sustainability and that the complexity of the ecosystems require the evaluation of several parameters to define and monitor soil quality
Biological nitrogen fixation of soybean in acid soils of Sumatra, Indonesia
Waluyo, S.H. - \ 2000
Agricultural University. Promotor(en): W.M. de Vos; L. 't Mannetje; L.T. An. - S.l. : S.n. - ISBN 9789058082954 - 151
glycine max - sojabonen - bodembiologie - stikstoffixatie - stikstofbindende bacteriën - rhizobium - bradyrhizobium - inoculatie - entstof - biochemische technieken - dna-fingerprinting - stamverschillen - stammen (biologisch) - zaadbehandeling - omhullen - zure gronden - bodemaciditeit - bekalking - sumatra - indonesië - glycine max - soyabeans - soil biology - nitrogen fixation - nitrogen fixing bacteria - rhizobium - bradyrhizobium - inoculation - inoculum - biochemical techniques - dna fingerprinting - strain differences - strains - seed treatment - pelleting - acid soils - soil acidity - liming - sumatra - indonesia
The aim of this study is to improve soybean cultivation in transmigration areas, especially in Sitiung, West Sumatra. However, these soils are very acid, and have a high P-fixing capacity. To reduce the amounts of fertilisers, normally 5 - 7 ton lime ha -1 and 100 kg P as TSP, seed, pelleted with lime (60 kg ha -1 ) and TSP (10 kg ha -1 ), was introduced. In this way only 2 ton lime ha -1 are required.
Soybean can fix nitrogen (BNF) in symbiosis with ( Brady ) Rhizobium bacteria. However, these acid soils in general, have low numbers of ( Brady ) Rhizobium . By inoculating the soils with ( Brady ) Rhizobium , BNF of soybean, and yield, were considerably improved.
A study was made of the indigenous ( Brady ) Rhizobium population in view of the following:
Using molecular techniques, indigenous strains derived from soil samples from old soybean areas (Java) and from new soybean areas (Sumatra) were classified in more detail. Most likely B. japonicum is the dominant strain in Java while in Sumatra B. elkanii is more present. A Sinorhizobium fredii -like strain was isolated from one soil sample from Java.