Endogenous Knowledge and Morphological Characterization of Cassava (Manihot esculenta Crantz) Accessions Found in Some Agricultural Areas of Gabon

Gino Boussiengui-Boussiengui^*, René Noël Poligui, Christie Yaëlle Massounga, Henri Nzandi, Pherla Ichida Oyanadigui Odjoueri, Armel Mouketou Mouketou, Denis Assey, Antoine Mitte Mbeang Beyeme, Christian Moupela

Département de Phytotechnologie, Institut National Supérieur d’Agronomie et de Biotechnologies, Université des Sciences et Techniques de Masuku, Franceville, Gabon.

DOI: 10.4236/ojapps.2025.156114                

Abstract

Cassava is a food crop that contributes to food security and is well established in Gabon. Taking into account endogenous knowledge and the dynamics of accessions agrobiodiversity at national level is necessary to undertake conservation strategies to reduce genetic erosion. Based on a participatory survey approach with field visits and data collection, 43 villages spread over seven (7) departments comprising 13 socio-cultural groups were surveyed. In the villages surveyed, 82.75% of cassava cultivation is carried out by women and 54.55% by farmers under 55 years of age. Of the 110 farms visited, 93.64% are individual farms and 6.36% are cooperatives found exclusively in the provinces of Woleu Ntem and Nyanga. The areas under individual use are less than 1 ha, compared with 5 - 22 ha for cooperatives. The harvest is done from 6 months for early accessions and 12 months for late ones. As for the cuttings, it is done in old plantations aged 8 to 12 months. A main component analysis (PCA) although low (22.50%) confirms morphological variability. In addition to the major descriptors (color of the apical leaf, color of the main rib, color of the petiole and sometimes color of the terminal branch), endogenous knowledge of cassava accessions is based on the phenotypic characteristics, the place of origin or on the introducer of the accession in the locality. The Hierarchical Ascending Classification (AHC) has allowed the structure of these accessions in 3 groups of morphological diversity. Group 1 consists of accessions with a small first branching height (<1 m) and a large branching angle (>90˚). Group 2 comprises individuals with a larger first branching height (>1.35 m) and a low branching angle (<90˚). In the third group, accessions are mainly characterized by the absence of branching. The identification of these different groups offers a great opportunity for the creation of improved cassava varieties in Gabon.

Keywords

Cassava, Accessions, Gabon, AHC, PCA

1. Introduction

Cassava (Manihot esculenta Crantz) originates from Latin America and is increasingly grown in tropical and subtropical regions. In the tropics, it is the primary source of calories [1] (Dixon et al., 2002) and the source of income for small farmers. It is considered one of the main sources of carbohydrates, being a staple food mainly for people in Latin America and Africa [2] (Alvarez et al. 2007), which use both tuberosilic roots as a rich source of starch and, the leaves as source of protein, minerals and vitamins [3] (Ceballos, 2012). The crops were introduced in Gabon after the first world war by cultivars returning from Congo [4] (Raponda-Walker and Sillans, 1961).

Due to its easy cultivation, year-round availability, and tolerance to extreme ecological and biotic stress conditions, a wide variety of cassava genotypes can be found in the growing areas [5] (Lozano, 1985), [6] (Nweke et al.,1994), [1] (Dixon et al., 2002). The diversity is due to the fact that genotypes respond differently to different climatic and biotic factors, while also the constant exchange of genetic material among cassava farmers [7] (Maroya, 1997). Some of these characters can be relevant for varietal improvement and breeding programs. Indeed, [8] (Fukuda and Guevara, 1998) indicated that the evaluation of the existing genetic variability is necessary and must be based on appropriate and recognized descriptors.

According to [9] (Hahn, 1979), the movement of cassava plant material between producers not only preserves and protects varietal diversity, but also provides indications of the preferences of farmers for cassava in a country or agro-ecological zone.

To better express these preferences, producers distinguish the different cassava genotypes by local names that are generally descriptive of the physical characteristics of the plants, such as the color of certain organs, size and type of foliage, yield potential and production cycle etc. These names may also describe the original source of the genotype or indicate an event that coincides with the introduction of the genotype [7] (Maroya, 1997). Despite their significance, these names are of little use in a botanical classification of different varieties because the same variety can have several names from one village to another or from one ethnical group to another.

To our knowledge, few studies on the analysis of endogenous knowledge and phenotypic characterization of cassava varieties have been done in Gabon except for some unpublished works by the Ministry of Agriculture describing some varieties in a non-exhaustive way.

The aim of this study is to identify the morphological characteristics of cassava accessions encountered in agricultural areas of Gabon. Specifically, this work aims to inventory cassava accessions present in the areas surveyed, identify key criteria for recognition of accessions, and analyze morphological variability within the cassava accessions encountered.

2. Materials and Methods

2.1. Site Selection Criteria and Data Collection Methodology

The study was carried out between 2018 and 2020 in some agricultural areas of the provinces of Woleu Ntem, Ngounié, Ogooué-lolo, Moyen Ogooué, Nyanga and Haut-Ogooué in Gabon including seven (7) departments (Figure 1). The choice of locations and farmers was made not only on the basis of accessibility, but also their ability to identify different accessions in local languages.

Figure 1. Location of prospected sites for the study.

Data were collected during expeditions from the different sites through the application of participatory research appraisal tools and techniques, such as direct observation, group discussions, individual interviews, and field visits using a questionnaire following [10] (Adjatin et al., 2012), [11] (Kombo et al., 2012). In each village, interviews were conducted with the help of a local translator and groups surveyed were made of 5 to 10 farmers of both sexes and of different ages identified and assembled with the assistance of the local farmers’ associations and the chief of the village involved in the study to facilitate the organization of the meetings and the collection of data according to [11] (Kombo et al., 2012).

2.2. Measured Parameters

Seventeen variables were determined, including 12 qualitative and 06 quantitative. Three plants/accessions were measured and observed. All of its measurements and observations were made according to the criteria defined by [12] (Fukuda et al., 2010). Qualitative variables are essentially the color of the apical leaves (CAL), the shape of the central leaflet (SCL), the color of the leaf vein (CLV), the petiole color (CP), the color of the stem cortex (CSC), color of mature leaf (CML), the color of stem epidermis (CSE), color of end branches (CEB), external color of the root (ECR), the color of root cortex (CRC) and the color of root pulp (CRP). For quantitative variables, the number of lobes (NL), length of petiole (LP), distance between leafs scars (DLS), height of first branch (HFB), diameter at the neck of the main stem (DNS) and angle of first branch (AFB).

2.3. Statistical Analysis of Data

The matrix of data composed of the means of quantitative variables and the different modalities of qualitative variables was used to carry out a Principal Component Analysis (PCA). The variables that contribute most to axis formation were defined as active variables and the rest as additional variables. An Ascending Hierarchical Classification (AHC) then allowed to classify accessions into homogeneous groups according to the Ward method using a similarity index of the Euclidean distance. These multivariate analyses were performed using the XLSTAT 2022 software.

3. Results and Discussion

3.1. Characteristics of the Prospected Area

The data related to the villages and socio-cultural groups, characteristics of the farms, age distribution and gender approach are respectively presented in Tables 1-3.

Table 1. List of prospected villages and socio-cultural groups.

Number	Villages	Departements	Provinces	Socio-cultural groups
1	Makongola	Lolo-Bouenguidi	Ogooué Lolo	Nzebi
2	Mayang	Lolo-Bouenguidi		Nzebi
3	Aéroport	Lolo-Bouenguidi		Massango
4	Ngoungui	Lolo-Bouenguidi		Pouvi
5	Camp militaire	Lolo-Bouenguidi		Massango
6	Mabimbi	Lolo-Bouenguidi		Akélé
7	Ikembelé	Lolo-Bouenguidi		Akélé, Massango, Nzébi
8	Makongola	Lolo-Bouenguidi		Nzébi
9	Kounadémbé	Lolo-Bouenguidi		Massango
10	Mokabo	Douya Onoye	Ngounié	Mitsogo
11	Moukidi	Douya Onoye		Punu
12	Mouila	Douya Onoye		Punu, Nzébi
13	Mouyamba	Louetsi Wano		Massango
14	Lebamba	Louetsi Wano		Nzébi
15	Adzabikat	Woleu	Woleu Ntem	Fang
16	Elop	Woleu
17	Abang-Medoumou	Woleu
18	Essong Medzome	Woleu
19	Mbam Assengma	Woleu
20	Nzela Bola	Ogooué et Lacs	Moyen Ogooué	Nzébi/Woumbou
21	Koungoule	Ogooué et Lacs		Echira/Fang
22	Lobi-Mbigou	Ogooué et Lacs		Massango
23	Mbolet	Ogooué et Lacs		Akélé/Nzébi
24	Issala II	Ogooué et Lacs		Massango
25	Mitoné	Ogooué et Lacs		Mièné/Fang
26	Massika	Ogooué et Lacs		Punu/Mitsogo
27	Mouroumbi	Mougoutsi	Nyanga	Punu
28	Mabotsa	Mougoutsi		Loumbou
29	Manfila	Mougoutsi		Loumbou
30	Moumbatsi	Mougoutsi		Punu
31	Payilou	Mougoutsi		Punu
32	Mouhanzi	Mougoutsi		Loumbou
33	Bidembe	Mougoutsi		Punu
34	Gorde	Mougoutsi		Punu
35	Ilama	Mougoutsi		Punu
36	Midjongou	Mougoutsi		Punu
37	Ossolé	Plateaux	Haut-Ogooué	Téké
38	Odjouma	Plateaux
39	Ampou	Plateaux
40	Akou	Plateaux
41	Souba	Plateaux
42	Abouyi	Plateaux
43	Eau clair	Plateaux

Table 2. Characteristics of the farms found in agricultural areas.

No	Province	Departement	Exploitation	Total	Area (ha)	Harvest (month)	Cutting (month)
1	Haut Ogooué	Plateaux	Cooperative	0	-	≥8	≥8
			Personal	31	≤1
2	Moyen Ogooué	Ogooué et Lacs	Cooperative	0	-	≥12	12
			Personal	15	≤1
3	Woleu Ntem	Woleu	Cooperative	4	≥5	≥6	≥8
			Personal	2	≤1
4	Nyanga	Mougoutsi	Cooperative	3	≥10	≥8	≥8
			Personal	19	≤1
5	Ogooué Lolo	Lolo Bouéguidi	Cooperative	0	-	≥8	≥8
			Personal	20	≤1
6	Ngounié	Doya/Louétsi wano	Cooperative	0	-	≥12	≥8
			Personal	16	≤1
Total	6	8		110
			Cooperative	7 (6.36%)	[5 - 22]	[6 - 12[	[8 - 12]
			Personal	103 (93.64)	≤1

Table 3. Age distribution of respondents and gender approach.

	Characteristics
Ages	Total	Women	Men
[30 - 55[	60 (54.55%)	50 (54.95%)	10 (52.63%)
[55 - 77]	50 (45.45%)	41 (45.05%)	9 (47.37%)
Total	110 (100%)	91 (82.73%)	19 (19.27%)

Except Haut Ogooué (Plateaux Department) and Woleu Ntem (Woleu Department) where only one dominant socio-cultural group is found, the rest of the prospected area is composed of farmers from two (2) to nine (9) socio-cultural groups (Table 1). This can be explained by the fact that those two departments are populated by only one ethnic group (Fang for Woleu Department and Téké for Plateaux Department), which is not the case for the other prospected area, where the highest socio cultural group diversity was found in the Department of Ogooué and lacs.

Out of the six (6) provinces and the seven (7) departments surveyed, 93.64% are personal farms (planting area ≤ 1 ha) against 6.36% of cooperatives (planting area between 5 and 22 ha) found only in Nyanga and Woleu Ntem provinces (Table 2). Similar results were observed by [13] (Amadi et al., 2020) where farms use less than 1ha and 80% - 82% did not belong to a cooperative society in Imo state of Nigeria. In this study, the presence of cooperatives is justified by the implementation of the PDAR (“Projet de Développement Agricole et Rural”), with the help of IFAD (International Fund for Agricultural Development). The project plans on developing nurseries for peanuts, plantains and cassava, and promoting the creation and organization of local farming cooperatives, while providing the facilities for the transformation and commercialization of farm products.

Regarding age and gender approach, 54.55% of farmers are under 55 years old and 45.45% are aging between 55 and 77 years old, with women representing 82.73% of active farmers (Table 3). Similar results suggest that cassava farming is practiced more by women than men [14] (Nwaobiala et al., 2019), [15] (Claudette and Roger, 2022). Also, the average age of cassava farmers across Cameroon regions is 42.2 years [15] (Claudette and Roger, 2022), lower than the average of 53.5 years observed in agricultural areas of Gabon and confirmed by [16] (Mouketou et al., 2023).

3.2. Endogenous Knowledge: Key Criteria for Recognition of Cassava Accessions by Farmers

Group discussions, individual interviews with cassava producers, and field visits using a questionnaire were done to determine the recognition criteria. The major criteria are presented in Figure 2.

Figure 2. Major criteria for recognition of cassava accessions by producers. CSE: color of the stem exterior, CEB: color of end branches, CML: color of mature leaf, ECR: External color of the storage root, PC: petiole color, CAL: color of apical leaves, SCL: shape of central leaflet.

In Gabon, more than 85% of farmers distinguish different cassava accessions based on the morphological characteristics, origin and introducer (Figure 2). The seven (7) morphological characteristics are the color of the stem exterior (CSE), the color of end branches (CEB), the color of mature leaf (CML), the external color of the storage root (ECR), the petiole color (PC), the color of apical leaves (CAL) and the shape of central leaflet (SCL). The analysis of morphological characteristics in various organs showed variations within the studied accessions. Color appears to be the most representative and similar results were obtained by [17] (Asare et al., 2011), [18] (Doussouh et al., 2016), [19] (Nadjiam et al., 2016), [20] (Djaha et al., 2017). In addition, [21] (Agre et al., 2016) have reported that farmers use the colors of the leaves and stems to identify the cassava cultivars. Also, the inter-ethnic union through filiate links or by purchasing cuttings would have favored this exchange of accessions. Hence, the presence of cultivars bearing names of their origins (Ongali, Akiéni) or people (Nzaou, Pauline) who would have introduced them into a locality. According to [22] (Delêtre, 2010) and [20] (Djaha et al., 2017), this designation often leads to confusion since the same accession may have different names depending on the area of cultivation but also the language.

3.3. Variability of Diversity in the Prospected Provinces

In total, 211 accessions were recorded in the six (6) provinces prospected, where the highest number of 51 accessions were found in Haut Ogooué, 44 in Ogooué Lolo, 42 in Moyen Ogooué and 39 in Nyanga (Table 4). Except for Haut Ogooué, where 86.27% of the accessions are bitter, the rest of the provinces cultivate more than 56% of sweet accessions.

Table 4. Variability of the number of local cassava accessions by provinces.

No	Provinces	Total accessions	Sweet accessions (%)	Bitter accessions (%)
1	Haut Ogooué	51	7 (13.73%)	44 (86.27%)
2	Moyen Ogooué	42	31 (73.80%)	12 (26.19%)
3	Woleu Ntem	14	8 (57.14%)	6 (42.86%)
4	Nyanga	39	30 (76.92%)	9 (23.08%)
5	Ogooué Lolo	44	25 (56.82%)	19 (43.18%)
6	Ngounié	21	14 (66.67%)	7 (33.33%)
Total	6	211	115 (54.50%)	97 (45.50%)

High levels of accession diversity, however, do not necessarily imply high levels of genetic diversity since out of the 211 recorded accessions, only 98 were different to each other. The distinctness can arise from a combination of environmental and recognition factors. Different collection sites may have resulted in capturing unique genotypes or phenotypes, contributing to the distinct count. Variability in environmental conditions (e.g., soil type, climate) where accessions were collected can lead to phenotypic differences, even among genetically similar plants. The initial sample size may have included duplicates or closely related accessions that were not genetically distinct, leading to a higher number and less distinct accessions when duplicates are removed.

There are several mechanisms through which diversity can be increased locally, the most important of which is the dissemination of accessions alongside the flow of people. This was confirmed by [22] (Delêtre, 2010) in its works on manioc diversity in Gabon. Exchanges of cuttings between farmers were extremely frequent in the prospected areas and represented the principal medium for farmers to acquire new accessions. But repeated and independent introductions of the same accession in a village, or the simple deformation of the original name while the accession passes down the generations and circulates among farmers, can generate synonymies, thereby artificially increasing diversity. This was also confirmed by [22] (Delêtre, 2010).

The observed higher level of bitter accessions in Haut Ogooué province compare to the other provinces can be explained by the dietary habits. In fact, in Plateaux Department, cassava sticks and fufu are staple foods, and adequate preparation before eating are therefore crucial steps for reducing the natural hydrocyanic acid [23] (Montagnac et al., 2009). In the other provinces, in addition to above mentioned staple food, cooked cassava tuber is used which may justify the presence of 56% to 77% of sweet accessions.

3.4. Principal Component Analysis (PCA)

Multivariate analyses are statistical methods used in diversity analysis. In this study, multivariate analyses were used to elucidate the nature and degree of divergence of cassava accessions collected in different agro-ecological zones of Gabon. The PCA, applied to the 98 accessions on the basis of 17 morphological variables (11 qualitative and 6 quantitative), results in a low variability (25.12%) within the accessions analyzed and revealed by the first two axes. The data might have low inherent variability, suggesting that the traits do not change much across observations. It suggests that many qualitative characters are correlated or redundant, they may not contribute significantly to overall variance and the PCA may capture only a small amount of the total variability. This variability is lower than that observed by [24] (Ephrem et al., 2014) in the Central African Republic and [21] (Djaha et al., 2017) in Côte d’Ivoire. Indeed, these authors obtained variabilities of 55% and 63.84%, respectively.

The lower variability observed in this work can be explained by not only the higher exchange rate of accessions between farmers, but also similarities observed within accessions bearing different names from one agricultural zone to another. Duplicates in cassava were often highlighted by several authors in numerous collections throughout the world [17] (Asare et al., 2011), [25] (N’Zue et al., 2014), and different accessions can have the same name or several names can be assigned to one accession [26] (Elias et al., 2011). Exchanges of cuttings between farmers were extremely frequent in the prospected areas, and represented the principal medium for farmers to acquire new accessions [22] (Delêtre, 2010). But, repeated and independent introductions of the same accession in a village, or the simple deformation of the original name while the accession passes down the generations and circulates among farmers, can generate synonymies, thereby artificially increasing diversity [22] (Delêtre, 2010) (Figure 3).

Figure 3. Distribution of variables and accessions in plan 1 - 2 revealed from the PCA for the 98 cassava accessions.

3.5. Ascending Hierarchical Classification (AHC)

The ascending hierarchical classification of the 98 accessions based on qualitative (11) and quantitative (6) traits classified into three groups with similar characteristics as a function of the variable (Figure 4). The genetic similarity for the 17 traits ranged from zero to three hundred, with a mean similarity of 300. The cassava accessions were grouped into three distinct clusters with similarities of 54.59. Similar results were observed by [20] (Djaha et al., 2017) and [25] (N’Zue et al., 2014). Nevertheless, in their work on cassava accessions, [27] (Ampong-Mensah, 2000) in Ghana and [28] (Bolamba et al., 2024) in RD Congo obtained four homogeneous groups.

The main Characteristic of the three groups where based on the height of the first branching (HFB), the angle of the first branching (AFB), the length of the petiole (LP), the distance between leafs scars (DLS), and the diameter at the neck of the main stem (DNS) (Table 5) and on qualitative traits (Table 6). Group I and 2 contain 45 accessions each and Group 3 contains 8 accessions. The AHC shows a strong phenotypic organization based essentially on the five (05) quantitative variables mentioned above. Similar results were reported by [20] (Djaha et al., 2017). However, [17] (Asare et al., 2011) found that the length of the central lobe and the color of the petiole are the most relevant variables for distinguishing cassava accessions in Ghana. This contradiction could be explained by the difference between the two places of collection and the environmental conditions.

Branching can influence the number of tuber produced and breeding for optimal branching can enhance yield potential. Accessions with specific branching habits may have better air circulation and reducing disease incidence. Understanding branching can help in developing appropriate agronomic practices for different environments. Utilizing the genetic variability within the accession groups helps in selecting diverse parental lines, which can enhance the potential for heterosis (hybrid vigor). Hybridization between different accession groups can

Figure 4. Ascending hierarchical classification of the 99 accessions found in the agricultural zones of Gabon.

Table 5. Characteristic of groups from the Ascending Hierarchical Classification.

Variables	Group 1	Group 2	Group 3
N	45	45	8
HFB	78.62 ± 10.24b	136.63 ± 27.10a	0c
AFB	115.13 ± 11.59a	85.83 ± 9.92b	0c
PL	20.38 ± 3.19a	15.07 ± 3.34b	21.13 ± 3.34b
DLS	4.07 ± 1.79a	3.39 ± 1.15b	2.75 ± 1.25b
DNS	2.82 ± 0.69a	2.57 ± 0.67a	2.38 ± 0.46a

On the lines, the averages followed by the same letter are statistically identical to the threshold α = 5%; Mean error type. N: number of accessions, HFB: height of first branching, AFB: angle of first branching, PL: petiole length, DLS: distance between leafs scars, DNS: diameter at the neck of the main stem.

Table 6. Classification of cassava accessions by group from the ascending hierarchical classification.

Accessions

CAL

SCL

CLV

PC

CML

CSE

CCS

CEB

ECR

CRC

CRP

Adzoro

Dark green

Lanceolate

Reddish-green L

Red

Dark green

Dark brown

Dark green

Green

Dark brown

White

White

Abegué

Dark green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green

Dark brown

Pink

White

Adjura

Purplish green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Dark brown

Dark green

Green-purple

Dark brown

Pink

White

Afuba mbong

Purplish green

Other

Reddish-green M

Red

Dark green

Cream

Dark green

Green-purple

Dark brown

Pink

White

Attend demain

Dark green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Light brown

Dark green

Green

Light brown

Pink

White

Beenvome

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green

Light brown

White

White

Dibutu

Purplish green

Elliptic-lanceolate

Green

Reddish-green

Dark green

Dark brown

Dark green

Purple

Light brown

White

White

Dicongu

Purple

Elliptic-lanceolate

Reddish-green L

Purple

Purple green

Light brown

Dark green

Purple

Light brown

Pink

White

Dicure

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green

Light brown

White

White

Dimbuanda

Purplish green

Elliptic-lanceolate

Green

Red

Dark green

Light brown

Orange

Green-purple

Dark brown

White

White

Dipandinu

Light green

Lanceolate

Green

Red

Light green

Light brown

Light green

Green

Light brown

White

White

Dogo mbong

Purplish green

Elliptic-lanceolate

Green

Reddish-green

Dark green

Light brown

Dark green

Green

Light brown

White

White

Ewo

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Dark brown

White

White

Fula

Dark green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Light brown

Dark green

Green

Dark brown

White

White

Gbaze

Purplish green

Elliptic-lanceolate

Green

Reddish-green

Dark green

Light brown

Dark green

Green

Light brown

White

White

Gnéghé

Light green

Lanceolate

Green

Red

Dark green

Light brown

Light green

Green

Light brown

White

White

Gungu

Light green

Lanceolate

Green

Yellowish-green

Dark green

Dark brown

Dark green

Green

Light brown

White

White

Kagnia

Dark green

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Dark brown

Dark green

Green

Dark brown

White

White

Kungu

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Dark brown

White

White

Kwata

Purplish green

Lanceolate

Reddish-green L

Greenish-red

Dark green

Light brown

Dark green

Green

Dark brown

White

White

Landura

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Cream

White

White

Madame violet

Purple

Lanceolate

Reddish-green M

Purple

Purple

Dark brown

Dark green

Purple

Dark brown

Pink

White

Mambikini

Purple

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Dark brown

White

White

Matadi

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green

Light brown

White

White

Mbomo

Dark green

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Light brown

Dark green

Green

Dark brown

White

White

Mbudu

Purple

Elliptic-lanceolate

Reddish-green L

Purple

Purple green

Light brown

Dark green

Purple

Dark brown

Pink

White

Mbwoyi

Purple

Lanceolate

Reddish-green M

Red

Dark green

Light brown

Light green

Green-purple

Dark brown

Pink

White

Messamoro mecom

Dark green

Elliptic-lanceolate

Reddish-green L

Greenish-red

Dark green

Light brown

Dark green

Green

Dark brown

White

White

Modzomba

Purplish green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Light brown

Dark green

Green

Light brown

White

White

Muduma

Purple

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Purple

Dark brown

White

White

Muvèpre

Purplish green

Elliptic-lanceolate

Green

Reddish-green

Dark green

Light brown

Dark green

Green

Dark brown

Pink

White

Ndambu

Dark green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Dark brown

Dark green

Green-purple

Light brown

White

White

Ngonabera

Purple

Elliptic-lanceolate

Reddish-green L

Purple

Dark green

Light brown

Dark green

Green-purple

Dark brown

White

White

Nombre

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Purple green

Light brown

Light green

Green-purple

Dark brown

White

White

Nsut mbong

Purple

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Light brown

Dark green

Green-purple

Dark brown

Pink

White

Nziéni

Purplish green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Light brown

Light green

Green-purple

Dark brown

White

White

Obira

Purplish green

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Dark brown

Light green

Green

Dark brown

White

White

Omonoyimi

Purplish green

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Dark brown

Light green

Purple

Dark brown

Pink

White

Onana

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Light green

Light brown

Light green

Green-purple

Light brown

White

White

Ongania

Purplish green

Elliptic-lanceolate

Green

Green

Dark green

Light brown

Light green

Green

Light brown

Pink

White

Ononeberé

Purplish green

Elliptic-lanceolate

Green

Reddish-green

Dark green

Dark brown

Dark green

Green

Dark brown

White

White

Opipi

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green

Dark brown

White

White

Opupu

Purplish green

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Light brown

Dark green

Green

Light brown

White

White

Pauline

Light green

Lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Dark brown

White

White

Yabwa

Purple

Elliptic-lanceolate

Reddish-green M

Purple

Purple green

Light brown

Dark green

Green-purple

Dark brown

Pink

White

Alen mbong

Dark green

Elliptic-lanceolate

Reddish-green M

Purple

Dark green

Dark brown

Dark green

Green

Dark brown

Pink

White

Bilongu

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Purple

Dark brown

Pink

White

Bilongu bi pahe

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Orange

Green

Light brown

Cream

White

Buadra

Purplish green

Lanceolate

Green

Greenish-red

Dark green

Dark brown

Light green

Green

Light brown

Pink

White

Bvodi-Bvodi

Dark green

Lanceolate

Green

Greenish-red

Dark green

Cream

Light green

Green

Light brown

Pink

White

Dimuma

Dark green

Lanceolate

Green

Greenish-red

Dark green

Cream

Light green

Green

Dark brown

Pink

White

Erhorla

Light green

Lanceolate

Green

Greenish-red

Dark green

Light brown

Light green

Green

Dark brown

Pink

White

Ilaboue

Purplish green

Elliptic-lanceolate

Green

Greenish-red

Dark green

Light brown

Dark green

Green

Light brown

Cream

White

Kobkob

Purplish green

Ovoid

Green

Red

Dark green

Dark brown

Light green

Green

Dark brown

Cream

White

Konongo

Purple

Elliptic-lanceolate

Reddish-green L

Greenish-red

Purple green

Dark brown

Dark green

Purple

Dark brown

Pink

White

Langoli

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Dark brown

Dark green

Green

Dark brown

Cream

White

Lenjangua

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Light green

Dark brown

Light green

Green

Light brown

Pink

White

Mabila

Purplish green

Lanceolate

Reddish-green M

Red

Dark green

Light brown

Light green

Green-purple

Light brown

Cream

White

Madame jaune

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Light green

Orange

Light green

Green-purple

Dark brown

Yellow

Yellow

Madjanga

Purple

Elliptic-lanceolate

Reddish-green M

Red

Dark green

Light brown

Light green

Green-purple

Dark brown

Cream

White

Mambia

Light green

Obovate-lanceolate

Reddish-green L

Red

Dark green

Cream

Light green

Green-purple

Light brown

Cream

White

Matzoma

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Light green

Light brown

Dark green

Green-purple

Dark brown

Cream

White

Motombi

Light green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Dark brown

Cream

White

Mouabi

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Light green

Light brown

Light green

Green

Light brown

Cream

White

Mugula-Mugula

Purplish green

Lanceolate

Reddish-green L

Reddish-green

Dark green

Dark brown

Light green

Green

Light brown

Cream

White

Munievu

Purplish green

Elliptic-lanceolate

Green

Greenish-red

Dark green

Light brown

Dark green

Green

Dark brown

Cream

White

Mupose

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Light brown

Cream

White

Mureké

Light green

Lanceolate

Reddish-green L

Greenish-red

Dark green

Light brown

Light green

Green

Dark brown

Pink

White

Musala

Purplish green

Elliptic-lanceolate

Reddish-green M

Red

Light green

Light brown

Light green

Green

Dark brown

Cream

White

Musavu guibi

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Dark brown

Cream

White

Ngudji

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green-purple

Dark brown

Cream

White

Nguya

Purple

Lanceolate

Reddish-green L

Red

Light green

Light brown

Dark green

Green

Light brown

Cream

White

Ngwali

Purplish green

Obovate-lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Light brown

Cream

White

Nkulu

Dark green

Elliptic-lanceolate

Green

Green

Dark green

Dark brown

Light green

Green

Dark brown

Cream

White

Nzaou

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Cream

Cream

White

Nzora

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Purple

Cream

Cream

White

Opwata

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Dark brown

Light green

Green-purple

Dark brown

Cream

White

Otsiémi

Purplish green

Lanceolate

Green

Red

Dark green

Light brown

Light green

Green

Dark brown

Cream

White

Ovèakima

Purplish green

Lanceolate

Reddish-green M

Red

Dark green

Dark brown

Dark green

Green

Dark brown

Pink

White

Oyendzé

Purplish green

Lanceolate

Green

Red

Dark green

Dark brown

Dark green

Green

Dark brown

Cream

White

Six mois

Purplish green

Obovate-lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Dark brown

Cream

White

Tsarimedju

Dark green

Elliptic-lanceolate

Green

Green

Dark green

Light brown

Dark green

Green

Dark brown

Cream

White

Tsarimekani

Dark green

Lanceolate

Reddish-green L

Greenish-red

Dark green

Light brown

Dark green

Green

Dark brown

Cream

White

Tseba

Purplish green

Lanceolate

Reddish-green L

Red

Light green

Light brown

Light green

Green

Light brown

Cream

White

Vivre

Purplish green

Elliptic-lanceolate

Reddish-green L

Greenish-red

Dark green

Dark brown

Light green

Green

Light brown

Cream

White

Voila

Purplish green

Lanceolate

Green

Red

Light green

Cream

Light green

Green

Dark brown

Cream

White

Wume

Purplish green

Elliptic-lanceolate

Reddish-green L

Reddish-green

Purple green

Light brown

Dark green

Green-purple

Dark brown

Cream

White

Yakaka

Purplish green

Lanceolate

Green

Greenish-red

Dark green

Light brown

Light green

Green

Light brown

Cream

White

Yala

Purplish green

Lanceolate

Reddish-green L

Red

Dark green

Light brown

Light green

Green

Dark brown

Pink

White

Yeme

Purplish green

Elliptic-lanceolate

Green

Greenish-red

Dark green

Cream

Dark green

Green

Light brown

Cream

White

Kayuoyo

Purplish green

Lanceolate

Green

Yellowish-green

Dark green

Light brown

Light green

Green

Dark brown

Cream

White

Ilongu

Purplish green

Elliptic-lanceolate

Reddish-green L

Reddish-green

Dark green

Light brown

Dark green

Green

Dark brown

Pink

White

Mbuangue

Purplish green

Lanceolate

Reddish-green M

Yellowish-green

Light green

Light brown

Light green

Green

Light brown

Cream

White

Musavu sakme

Purplish green

Elliptic-lanceolate

Reddish-green L

Red

Dark green

Light brown

Dark green

Green-purple

Light brown

Cream

White

Mutuku

Purplish green

Lanceolate

Green

Yellowish-green

Light green

Light brown

Dark green

Green

Light brown

Cream

White

Nzambe sakme

Purplish green

Elliptic-lanceolate

Green

Yellowish-green

Dark green

Light brown

Dark green

Green-purple

Dark brown

Cream

White

Ondumu

Purplish green

Oblang-lanceolate

Reddish-green L

Red

Dark green

Orange

Light green

Green

Light brown

Cream

White

Ongali

Purple

Elliptic-lanceolate

Green

Red

Dark green

Light brown

Dark green

Green

Light brown

Cream

White

CAL: color of apical leaves, SCL: shape of central leaflet, PC: petiole color, CML: color of mature leaf, CLV: color of leaf vein, CSE: color of stem epidermis, CCS: color of cortex stem, CEB: color of end branches, ECR: External color of the storage root, CRC: color of the root cortex, CRP: color of root pulp.

create new varieties with improved traits. This is particularly useful in developing cassava that is resilient to environmental stresses. Understanding the genetic makeup of the accession groups can aid in mapping traits of interest and developing targeted breeding strategies. Maintaining a diverse gene pool through these accession groups ensures the conservation of genetic resources, which is vital for long-term breeding success.

The analysis of qualitative characteristics in various organs showed variations within the studied accessions. Color appears to be the most representative and distinctive trait [17] (Asare et al., 2011) and [21] (Agre et al., 2016).

4. Conclusion

The study of the agro-morphological diversity of the 211 cassava accessions found in the prospected area in Gabon and their structuring on the basis of 17 descriptors showed variability with only 98 accessions clearly identified, indicating a high number of duplicates. This diversity was structured in 3 groups characterized by the height of the first branching, the angle of the first branching, the length of the petiole, the distance between leafs scars and the diameter at the neck of the main stem. This observed genetic variability between accessions is important for varietal breeding work. Breeding programs can effectively utilize the identified cassava accession groups to develop improved varieties that meet agricultural demands and environmental challenges.

Acknowledgements

Mr. Jonathan MBOULOU ELLA, Regional Director of Agriculture Woleu-Ntem and Ogooué-Ivindo, Mr. Serge ABESSOLO MBA, Director of Project PDAR/FIDA and the personnel, Mr. Edouard MASSALA, Regional Director of Agriculture Ngounié-Nyanga, Mr. BOUNGUILI Etienne, Provincial Director of Agriculture Ogooué-Lolo, Mr. Sévérin Arnaud BIBANG, Provincial Director of Agriculture Nyanga, Mr. Marius NZAOU, Provincial Director of Agriculture Moyen-Ogooué and Ms. Prisca IKOUELE IKOUETE, Agricultural Sector Plateaux. All of them for facilities and logistics.

Conflicts of Interest

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

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