Improving agroforestry and silvopastoral systems in Latin America by maximising species and genetic diversity of the multipurpose legume Inga

Tropical forest soils in the Amazon and many other parts of Latin America are generally nutrient-poor and unsuited to long-term agricultural use. Land converted to agriculture by cutting and burning natural vegetation tends to remain productive for only a few years, necessitating continual advance of the agricultural frontier, with accompanying deforestation, and generating situations of food insecurity and poverty.

Agroforestry and silvopastoral systems, which incorporate trees into crop and livestock systems, have been shown to make a dramatic impact on the maintenance and restoration of long-term productivity in agricultural landscapes, including degraded and abandoned land, and are well suited to use by poor rural smallholders. They can provide major benefits through enhanced livelihoods and food security, as well as to local economies.

Inga is a diverse genus of trees from the legume family, found across the humid tropics of Latin America. These fast-growing trees are able to capture nitrogen from the atmosphere and fertilise the soil around them. They can be grown in poor, degraded soils, out-competing weeds and invasive species.

The value of native trees, including Inga, within agroforestry systems, where they are planted to provide a nurturing environment for crops, has been amply demonstrated by a number of projects, and is gaining momentum. However, this has been insufficiently explored. Most such systems have been developed around a limited genetic stock of a single species, Inga edulis, yet it performs best under a limited range of conditions and other Inga species are likely to provide equal if not greater benefits outside of this range, which would expand the geographic and ecological scope within which these systems can be applied.

Emerging techniques in genetics offer the potential for rapid identification of species and genotypes of Inga with similar ecological characteristics, thus facilitating fast-tracking of appropriate candidates into field trials and ultimately into more productive landscapes. The project will apply state-of-the-art genetic approaches to complete a thorough analysis of the genus, focusing primarily on species in the Brazilian Amazon, identifying the most suitable species for agroforestry and silvo-pastoral systems. Critically, this selection of species will be done in consultation with stakeholders and smallholders, to ensure uptake and use of the selected species.

Targeted field collection of tissue specimens and seeds from these species will support ongoing genetic research, and will be used to establish early-stage field trials in Mato Grosso (southern Amazon), both in controlled contexts and in agroforest systems. These will be monitored to assess a range of characters including growth rate, biomass and tree form, all of which are important indicators of their suitability. Longer-term monitoring, using protocols developed by the project, will provide further indication of their potential value within these systems.

The project will be delivered in Brazil through collaborative partnerships between UK and Brazilian scientists. It aims to develop and demonstrate the effectiveness of a methodological approach that can form the basis for improved agroforestry and silvopastoral systems across Latin America. In the course of the project, the team will build a network of scientists and practitioners within Brazil and across other Latin American countries, facilitating the development of further research in this field and communicating its findings to a range of academics, practitioners of agroforestry and silvo-pastoral systems and the lay public, in both Latin America and the UK.

Existing agroforestry and silvo-pastoral systems (AF/SPS) in Latin America rely on few tree species that may be poorly adapted to specific edaphic environments and stakeholder needs. The proposed research will expand greatly the suite of tree species available for use in AF/SPS systems in moist tropical environments in Latin America, via a comprehensive research programme spanning from field trials to cutting-edge, next-generation sequencing approaches. We will focus on the hyperdiverse (~300 species) and ecologically dominant tree genus Inga (Leguminosae), for which we have already developed hybrid-capture protocols to efficiently sequence ~1400 genes, and for which field trials for AF/SPS have already been developed and implemented. In addition, the fact that Inga belongs to the economically important legume family allows us to leverage deep functional genetic, ecophysiological and agronomic knowledge to accomplish our key objectives.

We will increase our phylogenetic sampling of Inga (currently 135 species, mostly outside Brazil) to include multiple populations of all 93 Inga species present in the Brazilian Amazon. We will use this phylogenetic knowledge to determine which species are close relatives of the very few Inga species that are currently extensively used in AF/SPS systems. In consultation with stakeholders, we will implement field trials to determine which of these previously unused Inga species have the most desirable functional properties in terms of performance in AF/SPS systems. We will hold a workshop at the project's end, to diffuse this knowledge to key players in AF/SPS systems in Brazil, and elsewhere in Latin America, to expand the network and increase the efficiency of AF/SPS systems in Latin America. Lastly, we will leverage generated sequence data and existing transcriptomic data for 15 Inga species to determine which genetic loci underlie performance in field trials, which can improve future breeding improvement of Inga species.

The principal short- to medium-term impact of this project will be establishment of the scientific framework and collaborative partnerships necessary for the development of agroforest and silvopastoral systems for crop and livestock production that will contribute to more sustainable and productive agricultural landscapes in the humid Neotropics. The project will leave a lasting legacy including: (i) increased awareness, knowledge and uptake among scientists, practitioners and policy-makers of Inga systems; (ii) greatly improved knowledge of appropriate species and varieties of Inga for application within this context, achieved through the application of advanced molecular techniques and field trials supporting site-appropriate selection and breeding; (iii) new partnerships, alliances and technical approaches for further research and development in the region; and (iv) enhanced capacity for applied genomic research in Brazil applicable to agroforestry development and improvement more broadly.

In the longer term, in addition to future research built on the foundations of the project, the ultimate beneficiaries of our work will be rural communities in lower-middle income countries in Latin America. Via the greater resilience of agroforest and silvopastoral systems in times of climatic change and population growth, these communities can benefit from reduced poverty, improved food security, and reduced pressure on natural vegetation and biodiversity through conversion to agriculture. The outcomes from the project will therefore directly support Brazil in delivery of its commitments to the Convention on Biological Diversity and to the United Nations Sustainable Development Goals.