While modern agriculture relies on genetic homogeneity, diversifying practices associated with seed exchange and seed recycling may allow crops to adapt to their environment. This socio‐genetic model ...is an original experimental evolution design referred to as on‐farm dynamic management of crop diversity. Investigating such model can help in understanding how evolutionary mechanisms shape crop diversity submitted to diverse agro‐environments. We studied a French farmer‐led initiative where a mixture of four wheat landraces called ‘Mélange de Touselles’ (MDT) was created and circulated within a farmers' network. The 15 sampled MDT subpopulations were simultaneously submitted to diverse environments (e.g. altitude, rainfall) and diverse farmers' practices (e.g. field size, sowing and harvesting date). Twenty‐one space‐time samples of 80 individuals each were genotyped using 17 microsatellite markers and characterized for their heading date in a ‘common‐garden’ experiment. Gene polymorphism was studied using four markers located in earliness genes. An original network‐based approach was developed to depict the particular and complex genetic structure of the landraces composing the mixture. Rapid differentiation among populations within the mixture was detected, larger at the phenotypic and gene levels than at the neutral genetic level, indicating potential divergent selection. We identified two interacting selection processes: variation in the mixture component frequencies, and evolution of within‐variety diversity, that shaped the standing variability available within the mixture. These results confirmed that diversifying practices and environments maintain genetic diversity and allow for crop evolution in the context of global change. Including concrete measurements of farmers' practices is critical to disentangle crop evolution processes.
Since the domestication of crop species, humans have derived specific varieties for particular uses and shaped the genetic diversity of these varieties. Here, using an interdisciplinary approach ...combining ethnobotany and population genetics, we document the within‐variety genetic structure of a population‐variety of bread wheat (Triticum aestivum L.) in relation to farmers’ practices to decipher their contribution to crop species evolution. Using 19 microsatellites markers, we conducted two complementary graph theory‐based methods to analyze population structure and gene flow among 19 sub‐populations of a single population‐variety Rouge de Bordeaux (RDB). The ethnobotany approach allowed us to determine the RDB history including diffusion and reproduction events. We found that the complex genetic structure among the RDB sub‐populations is highly consistent with the structure of the seed diffusion and reproduction network drawn based on the ethnobotanical study. This structure highlighted the key role of the farmer‐led seed diffusion through founder effects, selection and genetic drift because of human practices. An important result is that the genetic diversity conserved on farm is complementary to that found in the genebank indicating that both systems are required for a more efficient crop diversity conservation.
Dans les années 2000, des agriculteurs désireux de cultiver des blés correspondant à leurs besoins et soucieux d’affirmer leur autonomie vis-à-vis de l’industrie semencière, ont entrepris de relancer ...la sélection paysanne à la ferme. Des collaborations ont été tissées avec des généticiens de l’Inra, et se sont progressivement développées dans le cadre de projets financés. Or les financements de recherche impliquent une formalisation des partenariats, des engagements en termes de résultats académiques et une augmentation significative de la taille des projets. Dans ce nouveau contexte, comment préserver les valeurs d’émancipation paysanne et de justice cognitive sur lesquelles la collaboration paysans-chercheurs s’est originellement construite ? Cet article aborde la façon dont ce défi se pose concrètement aux acteurs de ces projets, et les précautions qu’ils mettent en œuvre pour y faire face.
In the 2000s, a handful of farmers in France undertook to revive a practice fallen into disuse during agricultural modernization, i.e. on-farm plant breeding. Their motives were both to grow wheat varieties meeting their needs and to assert their independence towards the seed industry. Informal collaborations were woven with geneticists from the French institute for agronomic research (INRA), and developed further within the framework of funded projects. The foundations of a “decentralized participatory plant breeding” were then laid, both on a genetic rationale (breeding directly in the environments where the plants are to be grown) and on strong ethical principles (organizing non-hierarchical relations to let farmers question researchers’ assumptions). However, research funding involves a formalization of partnerships, commitments in terms of academic deliverables, and a significant increase in the size of projects. In this new context, how are the objectives of farmers’ empowerment and the values of cognitive justice on which the collaboration between farmers and researchers was originally built to be preserved? This article describes how this issue is actually tackled by the participants in these projects. We focus in particular on the debates raised by the creation of a database, and on the tensions it generates between centralization and decentralization. We also present the challenges raised by the dramatic increase in the number of participants, which risks to reproduce a division of tasks between researchers, farmers, and the people coordinating at a local level.
Key message
Calibrating a genomic selection model on a sparse factorial design rather than on tester designs is advantageous for some traits, and equivalent for others.
In maize breeding, the ...selection of the candidate inbred lines is based on topcross evaluations using a limited number of testers. Then, a subset of single-crosses between these selected lines is evaluated to identify the best hybrid combinations. Genomic selection enables the prediction of all possible single-crosses between candidate lines but raises the question of defining the best training set design. Previous simulation results have shown the potential of using a sparse factorial design instead of tester designs as the training set. To validate this result, a 363 hybrid factorial design was obtained by crossing 90 dent and flint inbred lines from six segregating families. Two tester designs were also obtained by crossing the same inbred lines to two testers of the opposite group. These designs were evaluated for silage in eight environments and used to predict independent performances of a 951 hybrid factorial design. At a same number of hybrids and lines, the factorial design was as efficient as the tester designs, and, for some traits, outperformed them. All available designs were used as both training and validation set to evaluate their efficiency. When the objective was to predict single-crosses between untested lines, we showed an advantage of increasing the number of lines involved in the training set, by (1) allocating each of them to a different tester for the tester design, or (2) reducing the number of hybrids per line for the factorial design. Our results confirm the potential of sparse factorial designs for genomic hybrid breeding.
Key message
We validated the efficiency of genomic predictions calibrated on sparse factorial training sets to predict the next generation of hybrids and tested different strategies for updating ...predictions along generations.
Genomic selection offers new prospects for revisiting hybrid breeding schemes by replacing extensive phenotyping of individuals with genomic predictions. Finding the ideal design for training genomic prediction models is still an open question. Previous studies have shown promising predictive abilities using sparse factorial instead of tester-based training sets to predict single-cross hybrids from the same generation. This study aims to further investigate the use of factorials and their optimization to predict line general combining abilities (GCAs) and hybrid values across breeding cycles. It relies on two breeding cycles of a maize reciprocal genomic selection scheme involving multiparental connected reciprocal populations from flint and dent complementary heterotic groups selected for silage performances. Selection based on genomic predictions trained on a factorial design resulted in a significant genetic gain for dry matter yield in the new generation. Results confirmed the efficiency of sparse factorial training sets to predict candidate line GCAs and hybrid values across breeding cycles. Compared to a previous study based on the first generation, the advantage of factorial over tester training sets appeared lower across generations. Updating factorial training sets by adding single-cross hybrids between selected lines from the previous generation or a random subset of hybrids from the new generation both improved predictive abilities. The CDmean criterion helped determine the set of single-crosses to phenotype to update the training set efficiently. Our results validated the efficiency of sparse factorial designs for calibrating hybrid genomic prediction experimentally and showed the benefit of updating it along generations.
Modern agricultural systems rely on reduced crop genetic diversity, due in particular to the use of homogeneous elite varieties grown in large areas. However, genetic diversity within fields is a ...lever for a more sustainable production, allowing greater stability and resistance to biotic and abiotic stresses. In France, a Participatory Plant Breeding (PPB) project on bread wheat, involving farmers, facilitators and researchers, has led to the development of heterogeneous populations whose within-variety genetic diversity is expected to confer the ability to adapt to farmers’ practices and environments. We studied the stability and local adaptation of ten of these farmers’ populations as well as two commercial varieties in relation to their within-variety genetic diversity. Although no clear evidence of local adaptation was detected, we found that populations’ grain yield and protein content were more stable over space and time respectively than those of commercial varieties. Moreover, the varieties’ stability over time in terms of protein content was positively correlated with within-variety genetic diversity with no significant drawback on protein yield. These results demonstrate the wide adaptive potential of PPB populations, highlighting the importance of seed exchange networks for agrobiodiversity management and use. They emphasize the benefits of genetic diversity for stability over time, which is of great interest to farmers.
Participatory plant breeding (PPB) is based on the decentralization of selection in farmers’ fields and their involvement in decision-making at all steps of the breeding scheme. Despite the evidence ...of its benefits to develop population varieties adapted to diversified and local practices and conditions, such as organic farming, PPB is still not widely used. There is a need to share more broadly how the different programs have overcome scientific, practical, and organizational issues and produced a large number of positive outcomes. Here, we report on a PPB program that started on bread wheat in France in 2006 and has achieved a range of outcomes, from the emergence of new organization among actors, to specific experimental designs and statistical methods developed, and to populations varieties developed and cultivated by farmers. We present the results of a two-year agronomic evaluation of the first population varieties developed within this PPB program compared to two commercial varieties currently grown in organic agriculture. We found that several PPB varieties were of great agronomic interest, combining relatively good performance even under the most favorable conditions of organic agriculture and good robustness, i.e., the ability to maintain productivity under more constraining conditions. The PPB varieties also tended to show a good temporal dynamic stability and appeared promising for the farmers involved.
Because organic systems present complex environmental stress, plant breeders may either target very focused regions for different varieties, or create heterogeneous populations which can then evolve ...specific adaptation through on-farm cultivation and selection. This often leads to participatory plant breeding (PPB) strategies which take advantage of the specific knowledge of farmers. Participatory selection requires increased commitment and engagement on the part of the farmers and researchers. Projects may begin as researcher initiatives with farmer participation or farmer initiatives with researcher participation and over time evolve into true collaborations. These projects are difficult to plan in advance because by nature they change to respond to the priorities and interests of the collaborators. Projects need to provide relevant information and analysis in a time-frame that is meaningful for farmers, while remaining scientifically rigorous and innovative. This paper presents two specific studies: the first was a researcher-designed experiment that assessed the potential adaptation of landraces to organic systems through on-farm cultivation and farmer selection. The second is a farmer-led plant breeding project to select bread wheat for organic systems in France. Over the course of these two projects, many discussions among farmers, researchers and farmers associations led to the development of methods that fit the objectives of those involved. This type of project is no longer researcher-led or farmer-led but instead an equal collaboration. Results from the two research projects and the strategy developed for an ongoing collaborative plant breeding project are discussed.
A participatory plant breeding (PPB) program involving the French farmers' association ‘Réseau Semences Paysannes’ and the French National Agricultural Research Institute (INRA) at Le Moulon was ...initiated in 2005. In the process of designing the breeding scheme, we evaluated the impact of farmer selection at an early stage (F2) on bread wheat cross progeny populations. The objectives were to characterize the effect of farmer selection, to evaluate the impact of farmer selection on intra-varietal diversity, to provide farmers with relevant information that they can use to improve their selection practices. Early selection was found efficient for some traits and for some of the 35 F2-derived F3 families. For traits of interest such as thousand kernel weight or grain weight per spike, when the response was significant, it was always positive. For most of the traits studied, the among-family genetic variance increased after selection while the average within-family genetic variance decreased. This study provides the first quantitative results for this PPB program and information that will help optimize it in the future.
Dans les années 2000, des agriculteurs désireux de cultiver des blés correspondant à leurs besoins et soucieux d’affirmer leur autonomie vis-à-vis de l’industrie semencière, ont entrepris de relancer ...la sélection paysanne à la ferme. Des collaborations ont été tissées avec des généticiens de l’Inra, et se sont progressivement développées dans le cadre de projets financés. Or les financements de recherche impliquent une formalisation des partenariats, des engagements en termes de résultats académiques et une augmentation significative de la taille des projets. Dans ce nouveau contexte, comment préserver les valeurs d’émancipation paysanne et de justice cognitive sur lesquelles la collaboration paysans-chercheurs s’est originellement construite ? Cet article aborde la façon dont ce défi se pose concrètement aux acteurs de ces projets, et les précautions qu’ils mettent en œuvre pour y faire face.
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