Agricultural production sustains human life across the globe, but nowhere does it face a more complex combination of socioeconomic and environmental constraints- or play a more central role in supporting livelihoods- than in the world’s tropical regions. In-country expertise and research capacity are expanding, and there is increasing recognition of the importance both of valuing local knowledge and sharing findings widely. Tropical agricultural research is therefore entering an exciting era- and the stakes are high. Climate change, emerging pests and diseases, and growing demand for food are just a few of the intense and mounting pressures on crop production. But right across the tropics, researchers are rising to the challenge. Here, we shine a spotlight on some recent PLOS ONE articles representative of the innovative agricultural research taking place in tropical countries and driving forwards the development of sustainable, resilient cropping systems.
Appropriate land management practices are at the heart of sustainable agriculture. Developing such practices requires a clear understanding of the relationships between soil properties and crop performance. One important focus of research is the effect of soil nutrient status on both growth and the production of secondary metabolites. For example, cassava can accumulate toxic cyanide when grown in nutrient-deficient soils, and Imakumbili and colleagues found that this explained the occurrence of neurological conditions in human populations in areas of Tanzania . It is also vital to understand how plants react to fluctuations in soil water content, such as through modification of root architecture, as studied using modelling approaches in pearl millet in Senegal by Faye and colleagues . Since the soil itself is of course the basis of all terrestrial crop production, accurate spatial mapping of soil properties can play a crucial role in planning crop deployment across complex landscapes. We have recently published examples of cutting-edge soil mapping projects from countries including Burkina Faso  and Ethiopia , based on a variety of techniques and with applications in sustainable agronomic practice.
Disease is a major challenge for tropical agriculture, with climatic conditions often being highly conducive to pathogen development and propagation. Monitoring programmes can help track endemic disease patterns as well as identifying dramatic long-distance dispersal events, such as the highly concerning arrival of wheat blast fungus in Zambia, recently reported in PLOS ONE . Modelling can also be used to explore the potential distribution and severity of diseases across geographical regions, as with the banana diseases black sigatoka  and fusarium wilt . Of course, understanding pathogen biology is also of fundamental importance, from pathological mechanisms to genetic diversity, which was the focus of Abidin and colleagues’ study of jackfruit bronzing disease . These authors found evidence for a high level of genetic uniformity in strains from across Malaysia, a result which will inform future surveillance and management strategies. Beyond the biological detail of host-disease interactions, research also focuses on modelling the impact of the disease on yield and production efficiency, as studied by Cerda and co-authors in the context of Costa Rican coffee .
Diverse crops and genes
Getting to grips with the diversity and structure in the germplasm of crops is key to unlocking their full potential. PLOS ONE has recently published important analyses of genetic diversity in tropical crops ranging from maize [10, 11] and cassava  to banana , yam , and sweet potato . These studies lay the groundwork for future crop improvement, as examined in the case of rice by Ali and colleagues . They described a breeding procedure with potential for improving rice plant tolerance to multiple environmental stresses. It is also widely recognised that more research is needed on the less well studied or ‘neglected’ crops in addition to the familiar staples that have traditionally attracted the vast majority of research funding. Neglected crops have enormous potential on many levels, as was recently highlighted in the case of Bambara groundnut in Zimbabwe by Mubaiwa and co-authors . They showed that more widespread adoption of this crop could confer significant benefits in terms of both nutrition and agricultural resilience.
Many tropical crops are cultivated in agroecological or agroforestry systems, where crops are grown in mixture with each other and with trees that provide a range of ecosystem services. These production systems are sometimes the product of long-established traditional practice, and other times the result of recent innovation. The scientific evidence base around these systems is ever-growing; recent articles in PLOS ONE cover the roles played by shade trees in plantations of cocoa in Ghana [18, 19] coffee in China , and banana in Guadeloupe . Elsewhere, relationships between agroecological management of coffee plantations and mycorrhizal fungi diversity was studied by Prates Júnior and colleagues in Brazil . They found that mycorrhizal diversity in agroecological plantations was significantly higher than in conventionally-managed plantations, and similar to in natural forest.
All tropical agriculture, whatever the crop or the location, will be impacted by climate change. Forecasts of the likely consequences of altered growing conditions on the viability of cropping patterns are an important tool to anticipate the need for agronomic adaptation, as in the case of a study by Duku and colleagues in Benin . They found that between 50% and 95% of cultivated areas in the Upper Ouémé watershed that currently support rainfed sequential cropping will be forced to revert to single cropping due to climate change. Models are also developed- using mechanistic or correlative approaches- to inform adaptation strategies for specific crops, as with cocoa in Brazil  and rice in the Philippines .
In the 21st century, tropical agricultural research is characterised by creative innovation, spurred by the many challenges of our times. New technological solutions for particular agronomic problems are reported frequently, as in the recent case of a spectroscopic tool for identification of barley, chickpea and sorghum cultivars in Ethiopia . The authors of this study also produced an accompanying R package for cultivar identification based on spectral data. Another consequence of the growing availability of communications technology among rural populations in the tropics is that it provides new opportunities for distributed research using citizen science methodologies, as studied by Beza and colleagues in Honduras, Ethiopia and India . They provide insights into the potential of technologically-enabled citizen science in tropical agriculture research, and identify ways of reducing barriers to participation.
Agricultural production does not take place in a vacuum. PLOS ONE has published a wide variety of research that addresses the socioeconomic contexts of tropical agricultural systems. For example, Volsi and colleagues have explored the dynamics of coffee production in Brazil in relation to policy environments and market forces , while Effendy and co-authors have looked at the factors driving the economic efficiency of cocoa production in Indonesia . Research elsewhere has examined the effects of the adoption of new cash crops for export on household food security and wellbeing and agroecological resilience, including in Guatemala  and Laos .
What directions will be explored in future tropical agriculture research? At one level, priorities for major research programmes are likely to be developed by national and supra-national institutes in the tropics, whose voices are taking their place on the global stage. However, there is recognition that research efforts should also be guided by the priorities of stakeholders at a regional and local level. This can involve direct consultation with farmers and regional experts, or quantitative modelling of priorities from multiple inputs, as in the study undertaken by Alene and colleagues in the context of cassava production in Africa, Asia and Latin America . Multi-stakeholder platforms (MSPs) have demonstrated great potential as vehicles for collaborative identification of research priorities and opportunities for innovation, though as highlighted in a social network study by Hermans and colleagues based in Burundi, Rwanda and the Democratic Republic of Congo, MSPs must be carefully orchestrated to achieve maximal connectivity and exchange of ideas and expertise .
PLOS ONE is a global community. We are proud to provide a venue for research on all aspects of tropical agricultural systems, including interdisciplinary work, new methods and technologies, and to make these findings freely available to all.
- Imakumbili MLE, Semu E, Semoka JMR, Abass A, Mkamilo G (2019) Soil nutrient adequacy for optimal cassava growth, implications on cyanogenic glucoside production: A case of konzo-affected Mtwara region, Tanzania. PLoS ONE 14(5): e0216708. https://doi.org/10.1371/journal.pone.0216708
- Faye A, Sine B, Chopart J-L, Grondin A, Lucas M, Diedhiou AG, et al. (2019) Development of a model estimating root length density from root impacts on a soil profile in pearl millet (Pennisetum glaucum (L.) R. Br). Application to measure root system response to water stress in field conditions. PLoS ONE 14(7): e0214182. https://doi.org/10.1371/journal.pone.0214182
- Forkuor G, Hounkpatin OKL, Welp G, Thiel M (2017) High Resolution Mapping of Soil Properties Using Remote Sensing Variables in South-Western Burkina Faso: A Comparison of Machine Learning and Multiple Linear Regression Models. PLoS ONE 12(1): e0170478. https://doi.org/10.1371/journal.pone.0170478
- Nyssen J, Tielens S, Gebreyohannes T, Araya T, Teka K, Van de Wauw J, et al. (2019) Understanding spatial patterns of soils for sustainable agriculture in northern Ethiopia’s tropical mountains. PLoS ONE 14(10): e0224041. https://doi.org/10.1371/journal.pone.0224041
- Tembo B, Mulenga RM, Sichilima S, M’siska KK, Mwale M, Chikoti PC, et al. (2020) Detection and characterization of fungus (Magnaporthe oryzae pathotype Triticum) causing wheat blast disease on rain-fed grown wheat (Triticum aestivum L.) in Zambia. PLoS ONE 15(9): e0238724. https://doi.org/10.1371/journal.pone.0238724
- Yonow T, Ramirez-Villegas J, Abadie C, Darnell RE, Ota N, Kriticos DJ (2019) Black Sigatoka in bananas: Ecoclimatic suitability and disease pressure assessments. PLoS ONE 14(8): e0220601. https://doi.org/10.1371/journal.pone.0220601
- Mostert D, Molina AB, Daniells J, Fourie G, Hermanto C, Chao C-P, et al. (2017) The distribution and host range of the banana Fusarium wilt fungus, Fusarium oxysporum f. sp. cubense, in Asia. PLoS ONE 12(7): e0181630. https://doi.org/10.1371/journal.pone.0181630
- Abidin N, Ismail SI, Vadamalai G, Yusof MT, Hakiman M, Karam DS, et al. (2020) Genetic diversity of Pantoea stewartii subspecies stewartii causing jackfruit-bronzing disease in Malaysia. PLoS ONE 15(6): e0234350. https://doi.org/10.1371/journal.pone.0234350
- Cerda R, Avelino J, Gary C, Tixier P, Lechevallier E, Allinne C (2017) Primary and Secondary Yield Losses Caused by Pests and Diseases: Assessment and Modeling in Coffee. PLoS ONE 12(1): e0169133. https://doi.org/10.1371/journal.pone.0169133
- Boakyewaa Adu G, Badu-Apraku B, Akromah R, Garcia-Oliveira AL, Awuku FJ, Gedil M (2019) Genetic diversity and population structure of early-maturing tropical maize inbred lines using SNP markers. PLoS ONE 14(4): e0214810. https://doi.org/10.1371/journal.pone.0214810
- Bedoya CA, Dreisigacker S, Hearne S, Franco J, Mir C, Prasanna BM, et al. (2017) Genetic diversity and population structure of native maize populations in Latin America and the Caribbean. PLoS ONE 12(4): e0173488. https://doi.org/10.1371/journal.pone.0173488
- Ferguson ME, Shah T, Kulakow P, Ceballos H (2019) A global overview of cassava genetic diversity. PLoS ONE 14(11): e0224763. https://doi.org/10.1371/journal.pone.0224763
- Nyine M, Uwimana B, Swennen R, Batte M, Brown A, Christelová P, et al. (2017) Trait variation and genetic diversity in a banana genomic selection training population. PLoS ONE 12(6): e0178734. https://doi.org/10.1371/journal.pone.0178734
- Arnau G, Bhattacharjee R, MN S, Chair H, Malapa R, Lebot V, et al. (2017) Understanding the genetic diversity and population structure of yam (Dioscorea alata L.) using microsatellite markers. PLoS ONE 12(3): e0174150. https://doi.org/10.1371/journal.pone.0174150
- Glato K, Aidam A, Kane NA, Bassirou D, Couderc M, Zekraoui L, et al. (2017) Structure of sweet potato (Ipomoea batatas) diversity in West Africa covaries with a climatic gradient. PLoS ONE 12(5): e0177697. https://doi.org/10.1371/journal.pone.0177697
- Ali J, Xu J-L, Gao Y-M, Ma X-F, Meng L-J, Wang Y, et al. (2017) Harnessing the hidden genetic diversity for improving multiple abiotic stress tolerance in rice (Oryza sativa L.). PLoS ONE 12(3): e0172515. https://doi.org/10.1371/journal.pone.0172515
- Mubaiwa J, Fogliano V, Chidewe C, Bakker EJ, Linnemann AR (2018) Utilization of bambara groundnut (Vigna subterranea (L.) Verdc.) for sustainable food and nutrition security in semi-arid regions of Zimbabwe. PLoS ONE 13(10): e0204817. https://doi.org/10.1371/journal.pone.0204817
- Asigbaase M, Sjogersten S, Lomax BH, Dawoe E (2019) Tree diversity and its ecological importance value in organic and conventional cocoa agroforests in Ghana. PLoS ONE 14(1): e0210557. https://doi.org/10.1371/journal.pone.0210557
- Abdulai I, Jassogne L, Graefe S, Asare R, Van Asten P, Läderach P, et al. (2018) Characterization of cocoa production, income diversification and shade tree management along a climate gradient in Ghana. PLoS ONE 13(4): e0195777. https://doi.org/10.1371/journal.pone.0195777
- Rigal C, Vaast P, Xu J (2018) Using farmers’ local knowledge of tree provision of ecosystem services to strengthen the emergence of coffee-agroforestry landscapes in southwest China. PLoS ONE 13(9): e0204046. https://doi.org/10.1371/journal.pone.0204046
- Tardy F, Damour G, Dorel M, Moreau D (2017) Trait-based characterisation of soil exploitation strategies of banana, weeds and cover plant species. PLoS ONE 12(3): e0173066. https://doi.org/10.1371/journal.pone.0173066
- Prates Júnior P, Moreira BC, da Silva MdCS, Veloso TGR, Stürmer SL, Fernandes RBA, et al. (2019) Agroecological coffee management increases arbuscular mycorrhizal fungi diversity. PLoS ONE 14(1): e0209093. https://doi.org/10.1371/journal.pone.0209093
- Duku C, Zwart SJ, Hein L (2018) Impacts of climate change on cropping patterns in a tropical, sub-humid watershed. PLoS ONE 13(3): e0192642. https://doi.org/10.1371/journal.pone.0192642
- Gateau-Rey L, Tanner EVJ, Rapidel B, Marelli J-P, Royaert S (2018) Climate change could threaten cocoa production: Effects of 2015-16 El Niño-related drought on cocoa agroforests in Bahia, Brazil. PLoS ONE 13(7): e0200454. https://doi.org/10.1371/journal.pone.0200454
- Stuecker MF, Tigchelaar M, Kantar MB (2018) Climate variability impacts on rice production in the Philippines. PLoS ONE 13(8): e0201426. https://doi.org/10.1371/journal.pone.0201426
- Kosmowski F, Worku T (2018) Evaluation of a miniaturized NIR spectrometer for cultivar identification: The case of barley, chickpea and sorghum in Ethiopia. PLoS ONE 13(3): e0193620. https://doi.org/10.1371/journal.pone.0193620
- Beza E, Steinke J, van Etten J, Reidsma P, Fadda C, Mittra S, et al. (2017) What are the prospects for citizen science in agriculture? Evidence from three continents on motivation and mobile telephone use of resource-poor farmers. PLoS ONE 12(5): e0175700. https://doi.org/10.1371/journal.pone.0175700
- Volsi B, Telles TS, Caldarelli CE, Camara MRGd (2019) The dynamics of coffee production in Brazil. PLoS ONE 14(7): e0219742. https://doi.org/10.1371/journal.pone.0219742
- Effendy, Pratama MF, Rauf RA, Antara M, Basir-Cyio M, Mahfudz, et al. (2019) Factors influencing the efficiency of cocoa farms: A study to increase income in rural Indonesia. PLoS ONE 14(4): e0214569. https://doi.org/10.1371/journal.pone.0214569
- Méthot J, Bennett EM (2018) Reconsidering non-traditional export agriculture and household food security: A case study in rural Guatemala. PLoS ONE 13(5): e0198113. https://doi.org/10.1371/journal.pone.0198113
- Thanichanon P, Schmidt-Vogt D, Epprecht M, Heinimann A, Wiesmann U (2018) Balancing cash and food: The impacts of agrarian change on rural land use and wellbeing in Northern Laos. PLoS ONE 13(12): e0209166. https://doi.org/10.1371/journal.pone.0209166
- Alene AD, Abdoulaye T, Rusike J, Labarta R, Creamer B, del Río M, et al. (2018) Identifying crop research priorities based on potential economic and poverty reduction impacts: The case of cassava in Africa, Asia, and Latin America. PLoS ONE 13(8): e0201803. https://doi.org/10.1371/journal.pone.0201803
- Hermans F, Sartas M, van Schagen B, van Asten P, Schut M (2017) Social network analysis of multi-stakeholder platforms in agricultural research for development: Opportunities and constraints for innovation and scaling. PLoS ONE 12(2): e0169634. https://doi.org/10.1371/journal.pone.0169634
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