Plant genetic resources are the key to food security and sustainable agricultural development. Indeed, climate change adaptation strategies are very costly for small family farms, which makes them very vulnerable. So, the diversification of crops appears as an alternative. The use of local varieties would constitute an opportunity for the populations because they occupy an important place in the diversification of plant resources [1] . Also, these so-called traditional varieties are genetically more diversified and better adapted to local conditions [2] [3] and their preservation contributes to maintaining the genetic richness [4] . Among the important crops maintained by West African farmers, fonio (Digitaria spp.) is probably the oldest African cereal [5] . Well adapted to local pedoclimate conditions, fonio is tolerant to drought due to its C4 metabolism and contributes to ecological protection by guaranteeing good plant cover on fragile and undervalued soils [6] . In traditional West African agrosystems, fonio, in addition to occupying a privileged place [7] . It plays a decisive role in preventing lean season [8] . Since the beginning of the 21st century, nutritionists have paid particular attention to this food because it is very digestible for people with allergies, especially in the case of gluten intolerance. Fonio can, therefore, also contribute to nutritional balance, which is still a growing concern in many countries. As a result, it is increasingly in demand in the sub-region and developed countries.

In Burkina Faso, fonio is used in the preparation of many traditional African recipes such as couscous, porridge, tô, and fatty fonio, which are often prescribed in the diet of some patients (diabetics) [9] . However, compared to the main cereal crops (rice, maize, sorghum and millet), fonio remains a minor plant in the Burkinabè agrarian system. It is mainly produced in the western part of the country. In addition, the arduous post-harvest treatment of fonio means that it is increasingly abandoned in some production areas. This could eventually lead to significant genetic erosion of the species in Burkina Faso. It is, therefore, necessary to preserve the local genetic resources of fonio and this requires knowledge of its genetic diversity. Indeed, genetic diversity studies carried out on cereals in Burkina Faso have mainly concerned maize [10] , millet [11] , rice [12] and sorghum [13] . These studies revealed significant variability at the level of morphological and molecular markers. However, the level of diversity and the structuring of this diversity of fonio grown in Burkina Faso remain very little known. The main objective of this study is the assessment of the agro-morphological variability of a collection of fonio produced in Burkina Faso. Specifically, the study aims at: 1) identifying the discriminating characters, 2) determining the relationships between the studied characters, and 3) establishing the level and structure of the diversity of the accessions created.

The characterization of the 60 accessions of fonio revealed significant phenotypic

Legend: The means assigned the same letter in the same column or the same row are not significantly different at the 5% level. Days to 50% emergence (DEM); Days to 50% tillering (DTA); Days to 50% flowering (DFL); Days to 50% maturity (DMA); Plant height at maturity (PHM); Total number of tillers per plant (TNT); Total number of internodes (TNI); Internodes length (INL); Leaf length (LLE); Leaf width (LWI); Spikelet grouping on pedicels (GSP); Exertion panicle length (EPL); Raceme size per plant (RSP); Total number of racemes per plant (TNR); 1000 grain weight (GrW); Grain weight per row (GWR); Dry biomass weight (BIO).

variability. Indeed, the significant differences between the characters of the accessions, the high coefficients of variation for most characters as well as the presence of modalities for certain qualitative characters reflect the existence of morphological variability within the accessions. The different color patterns of racemes, grains and stems observed during this study are similar to those observed by [1] within accessions of fonio in Niger based on grain color and stem color. According to these authors, this observed variability could be explained, in part, by the expression of one or more genes that govern these characters. Indeed, taking into account qualitative characters is very important in an agro-morphological characterization study insofar as these characters constitute characters of interest and selection criteria for the different actors. However, according to [15] [16] , an important number of qualitative characters retained among the descriptors do not often allow fine differentiation of the varieties of cultivated plants.

The variability within the collection offers opportunities for fonio breeding in Burkina Faso. However, the highly significant effect of the rainy season-genotype interaction on the observed variability reflects the influence of pedoclimate factors on the morphological performance of the accessions of fonio studied. Indeed, fluctuations in temperature and rainfall during the two rainy seasons would have influenced this variability. Aliero and Morakinyo [17] have already reported that day length, temperature and relative humidity have variable effects on the vegetative and physiological development of fonio. Additionally, [18] , on the study of the effect of the environment on the growth and yield characters of fonio accessions in Niger, revealed that the nature of the soil and the climate conditions influence the performance of the accessions of fonio.

The structuring of accessions independently of their geographical origin could be justified by the migratory flow of the population and the method of crop management, including seed exchanges between producers from one village to another neighboring or distant village which go that growers grow roughly the same accessions. Indeed, in addition to genetic factors, the level and structure of variability are generally influenced by non-genetic factors such as pedoclimate factors, population migration flows and crop management methods. Similar observations have been reported by [19] , who revealed that peasant seed management methods, in particular exchanges of varieties between farmers, are the source of significant diversity between fonios grown in the commune of Boukoumbé in Benin.

The morphological and phenological dissimilarities observed between the different phenotypic groups suggest that the accessions are maintained under very different evolutionary processes in their respective agroecosystem [1] . Agroecosystems are likely to exert highly variable selective pressures on genotypes [20] as well as anthropogenic pressures [21] . Indeed, the mode of seed management by farmers, such as selective sorting, post-harvest cultivation techniques and agricultural practices, lead to a selection leading to the maintenance or even the creation of significant phenotypic diversity [22] . Group I and Group III diversity with intermediate characteristics between early and late accessions could be the result of an adaptive process [1] . Fonio has not yet been the subject of real varietal selection and genetic improvement work in Burkina Faso, but the estimates made in this study could serve as a basis of comparison for subsequent investigations. Nevertheless, in Ivory Coast, [23] obtained similar phenotypic characters such as days to flowering, days to maturity, total number of tillers per plant, total number of nodes, total number of panicles, total number of leaves at the main stem, the height of insertion of the panicle which contributes better to the discrimination of four groups in the discriminant factor analysis.

The role played by phenotypic descriptors in the structuring of local varieties of fonio in Burkina Faso is not surprising, because it is a usual agronomic character for structuring variability in cereals. This would be linked to the difficulty for farmers to distinguish varieties other than by cycle length, a central character in management practices. Previous studies, based on the characters used by farmers, in particular the cycle, had highlighted the importance of the cycle in the characterization ok the accessions of fonio. Sekloka et al. [24] obtained slightly different results from ours. These authors highlighted two groups of fonio in Benin: an extra early group with a cycle of less than 90 days and a late group with more than 100 days. This observed difference could be explained by the fact that cultivars with cycle long are less appreciated by producers. According to [19] , very early cultivars mature during the rainy season and pose drying problems for growers. Similarly, cultivars that are too late do not manage to complete their cycle in good conditions.

The early accessions identified in this study are qualified as extra early to early according to the criteria proposed by [25] . Late accessions with higher biomass yield can be selected for livestock feed purposes thanks to their high fodder productivity.

Moreover, the percentage of variance accumulated by the four main axes of the principal component analysis is low (56.07%). These results would reflect the absence of a strong genotypic and phenotypic organization between the accessions [26] . Similar results were obtained by [23] in Côte d’Ivoire on fonio and several authors on other species [27] .

The agro-morphological characterization of accessions of Digitaria exilis shows the highlighted existence of diversity in Burkina Faso despite the narrowness of its area of cultivation. The results of this study have permitted to identify of important characters which permit to differentiate of the accessions, which are days to 50% flowering, days to 50% maturity, plant height at maturity, total number of tillers per plant, total number of internode, internodes length, leaf length, leaf width, exertion panicle length, total number of racemes per plant, grain weight per accession, and dry biomass weight. Since the role of local accessions in the plant resources of cultivated plants no longer needs to be demonstrated, particular attention must be paid to regions that ensure the sustainability of this source of variability. Thus, the characters analyzed can thus constitute basic criteria for differentiating the accessions of fonio of Burkina Faso and be used in studies of the morphological diversity of fonio in West Africa. The multivariate analyses have permitted to structure of the collection into 4 morphological groups. Exceptional morphotypes have been identified and could be considered as potential parents for future breeding work. It is mainly Nia4, Tou1, Nan1, Nia3, Nia6 which presented a high grain yield, Kan1, Com, Tap2, Tss1 and Bog1 presented a high dry biomass and Min1, Nou1, Bog1, Gbl2, Bor1, Dou2 presented a short cycle. However, taking agro-morphological characters only into account is not enough to produce a definitive and credible description. Indeed, the morphological characters, especially quantitative ones, are often strongly influenced by environmental factors. It is, therefore, important to do molecular analyses to invalidate or confirm the results obtained by the agro-morphological characterization.

The authors declare no conflicts of interest regarding the publication of this paper.

Patrice, B., Boukare, K., Mariam, K., Zakaria, K., Jacob, S. and Pauline, B./K. (2023) Agro-Morphological Characterization of a Collection of Fonio [Digitaria exilis (Kippist.) Stapf.] Accessions from Burkina Faso. American Journal of Plant Sciences, 14, 677-690. https://doi.org/10.4236/ajps.2023.146046