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Twenty Mimosa-nodulating bacterial strains from Brazil and Venezuela, together with eight reference Mimosa-nodulating rhizobial strains and two other ␤-rhizobial strains, were examined by amplified rRNA gene restriction analysis. They fell into 16 patterns and formed a single cluster together with the known ␤-rhizobia, Burkholderia caribensis, Burkholderia phymatum, and Burkholderia tuberum. The 16S rRNA gene sequences of 15 of the 20 strains were determined, and all were shown to belong to the genus Burkholderia; four distinct clusters could be discerned, with strains isolated from the same host species usually clustering very closely. Five of the strains (MAP3-5, Br3407, Br3454, Br3461, and Br3469) were selected for further studies of the symbiosisrelated genes nodA, the NodD-dependent regulatory consensus sequences (nod box), and nifH. The nodA and nifH sequences were very close to each other and to those of B. phymatum STM815, B. caribensis TJ182, and Cupriavidus taiwanensis LMG19424 but were relatively distant from those of B. tuberum STM678. In addition to nodulating their original hosts, all five strains could also nodulate other Mimosa spp., and all produced nodules on Mimosa pudica that had nitrogenase (acetylene reduction) activities and structures typical of effective N 2 -fixing symbioses. Finally, both wild-type and green fluorescent protein-expressing transconjugant strains of Br3461 and MAP3-5 produced N 2 -fixing nodules on their original hosts, Mimosa bimucronata (Br3461) and Mimosa pigra (MAP3-5), and hence this confirms strongly that Burkholderia strains can form effective symbioses with legumes.Although it was generally accepted for many years that legumes (and the nonleguminous plant Parasponia) were nodulated exclusively by members of the Rhizobiaceae in the ␣-Proteobacteria (including the genera Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium, and Sinorhizobium) (30, 34), recently there has been an increasing number of reports of members of the ␤-Proteobacteria being isolated from nodules. So far, these include Burkholderia tuberum strain STM678 and Burkholderia phymatum strain STM815 (originally isolated from Aspalathus carnosa in South Africa and Machaerium lunatum in French Guiana, respectively [26,39]), Ralstonia taiwanensis strains (isolated from Mimosa pudica in Taiwan and India and Mimosa diplotricha in Taiwan [8,41] and now renamed Cupriavidus taiwanensis [38]), and several Burkholderia strains isolated from Mimosa casta, Mimosa pigra (synonym, Mimosa pellita), M. pudica, and another mimosoid legume, Abarema macradenia, in Panama (3). Although symbiotic genes (nifH and nodA) have been identified in the Burkholderia strains STM678 and STM815, so far there is very little physiological and structural evidence of their symbiotic nature, and they have been shown to form only ineffective nodules on the promiscuous legume Macroptilium atropurpureum (26). More convincingly, not only have some of the Panamanian Burkholderia strains been shown to possess symbiosis-relat...

There is consensus that the global food system is not delivering good nutrition for all and is causing environmental degradation and loss of biodiversity, such that a profound transformation is needed to meet the challenges of persistent malnutrition and rural poverty, aggravated by the growing consequences of climate change. Agroecological approaches have gained prominence in scientific, agricultural and political discourse in recent years, suggesting pathways to transform agricultural and food systems that address these issues. Here we present an extensive literature review of concepts, definitions and principles of agroecology, and their historical evolution, considering the three manifestations of agroecology as a science, a set of practices and a social movement; and relate them to the recent dialogue establishing a set of ten iconic elements of agroecology that have emerged from a global multi-stakeholder consultation and synthesis process. Based on this, a consolidated list of principles is developed and discussed in the context of presenting transition pathways to more sustainable food systems. The major outcomes of this paper are as follows. (1) Definition of 13 consolidated agroecological principles: recycling; input reduction; soil health; animal health; biodiversity; synergy; economic diversification; co-creation of knowledge; social values and diets; fairness; connectivity; land and natural resource governance; participation. (2) Confirmation that these principles are well aligned and complementary to the 10 elements of agroecology developed by FAO but articulate requirements of soil and animal health more explicitly and distinguish between biodiversity and economic diversification. (3) Clarification that application of these generic principles can generate diverse pathways for incremental and transformational change towards more sustainable farming and food systems. (4) Identification of four key entry points associated with the elements: diversity; circular and solidarity economy; co-creation and sharing of knowledge; and, responsible governance to enable plausible pathways of transformative change towards sustainable agriculture and food systems.

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Fourteen strains were isolated from nitrogen-fixing nodules on the roots of plants of the genus Mimosa growing in Taiwan, Brazil and Venezuela. On the basis of 16S rRNA gene sequence similarities, all of the strains were previously shown to be closely related to each other and to belong to the genus Burkholderia. A polyphasic approach, including DNA-DNA reassociation, whole-cell protein analysis, fatty acid methyl ester analysis and extensive biochemical characterization, was used to clarify the taxonomic position of these strains: all 14 strains were classified as representing a novel species, for which the name Burkholderia mimosarum sp. nov. is proposed.

The increasing attention paid to local soil knowledge in recent years is the result of a greater recognition that the knowledge of people who have been interacting with their soils for long time can offer many insights about the sustainable management of tropical soils. This paper describes two approaches in the process of eliciting local information. Case studies show that there is a consistent rational basis to the use of local indicators of soil quality and their relation to improved soil management. The participatory process used is shown to have considerable potential in facilitating farmer consensus about which soil-related constraints should be tackled first. Consensus building is presented as an important step prior to collective action by farming communities in integrated soil management at the landscape scale. Taking advantage of the complementary nature of local and scientific knowledge is highlighted as an overall strategy for sustainable soil management. D 2002 Published by Elsevier Science B.V.

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