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Full project title: Understanding the determinants of the maize-bean association: agricultural practices, soil-plant interactions, nutrition. Project acronym: Co-culture.

Funded under the Call for Emergence 2016, the CoCulture project took place over 2 years (2017-2018)

Project leader: Maud TENAILLON (GQE-Le Moulon) Other people from this laboratory involved: L.Matthieu, J. Enjalbert, H. Corti, D. Manicacci

Partners:

• academic :
  • in BASC: UMR Agronomie, Grignon (M-H Jeuffroy)
  • Outside BASC: UMR Ecologie Microbienne Lyon (T. Trabac, D. Muller, Y. Moënne-Loccoz); UE du maïs, Saint-Martin-de-Hinx (C. Palafre, B. Lagardère); LISST-CAS; UMR Sol Agro hydrosytèmes Spatialisation, Rennes (V. Parnaudeau, E. Le Cadre).
• non-academic: Memento association, Toulouse (M. Carraretto)

The cultivation of maize and bean in association could benefit from the biological partnership between these two species through complementation and/or facilitation processes, in particular via the uptake of atmospheric nitrogen by the bean, which is possible thanks to a rhizospheric bacterial symbiosis. Despite the potentially interesting synergies between these species, no study has been done to describe the benefits of their association in cultivation. The aim of our project was to understand the functioning of this bispecific association in the case of Tarbais bean.

Species synergies allowing a more optimal sharing of resources could be at the origin of an increased yield in crops of species in association compared to monospecific crops, under low input conditions. Other benefits, such as improved competitiveness of associations against weeds, which reduces the need for herbicide treatments, and increased ecosystem services, could be mobilized. The challenge is to promote less input-intensive and more sustainable farming systems.

Seven farms in the Tarbes region were included in our study. We conducted interviews and took samples from plots of mono-specific crops (bean or corn) and associated crops: samples of "bare" soil and rhizospheric soil adhering to the roots to characterize bacterial assemblages, and samples of plants to analyze yield and nitrogen and carbon nutrition.

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• Interviews with farmers. The maize-bean combination is a traditional system that has been recently reintroduced. The Tarbais variety is used for beans, while for maize several rarely traditional varieties are chosen for their strong stalks and late flowering.
• Differences between intercropping (CA) and monospecific cropping (CM). In maize, vegetative biomass is higher in CA than in CM. In beans, grain size is larger but yield is lower in CA than in CM. Competition for grain production and carbon nutrition is observed between species. As for bacterial assemblages, the effect of CA/CM and cultural practices (farms) were significant on the qualitative composition of bacterial communities associated with roots.

Thanks to this project, we have been contacted to participate in a European H2020 project entitled "Intelligent Collections of Food Legumes Genetic Resources for European Agrofood Systems" which started last May. This project focuses on the description and conservation of European legumes, with a specific focus on the maize-bean association.

Our study revealed more competition than synergy between the two species. However, neither the growing conditions nor the choice of varieties were reasoned for this association; they were transferred from modern agricultural systems to be applied to a traditional agrosystem that was recently re-adopted. Through a thesis, we will seek to describe the genetic and phenotypic diversity of local maize and bean varieties collected in traditional European systems that have persisted (Romania and Italy), and compare the success of existing associations with those formed randomly to search for traces of coevolution between the two species and their genetic determinants.

The researcher explains the RESULTS in VIDEO (LabEx BASC scientific days, February 4, 2021)