IN-SITU MORPHOLOGICAL CHARACTERIZATION OF CASSAVA LANDRACES (MANIHOTESCULENTACRANTZ) FROM COTE DIVOIRE

Cassava provides food security for millions of people worldwide. In Cote dIvoire, it is the second most important food crop. The objective of this study is to evaluate the structure and genetic variability of certain qualitative traits in targeted cassava landracesin order to identify the most widespread cassava landraces. Thus, prospecting missions were carried out in different regions of Cote dIvoire to characterize cassavalandraces, from which 180 cassava landrace accessions were characterized using14 morphological markers. Multiple Correspondence Analysis (MCA) showed that among the 14 markers, 10 were relevant fordescribing the total variability within accessions. In addition, the Hierarchical Ascending Classification (HAC) grouped the Ivorianlandraces into five homogeneous groups and also revealed that this morphological diversity is not structured according to the landracesgeographical origin. The study highlighted 131 distinct cultivars among the 180 accessions characterized. Moreover, of the 131 distinct cultivars, four were the most widespread. These are the local cultivars: Yace, Six mois, BlÃƒÂªbou and Trogla. Thus, the study has definitively shown that breeders have a wide choice of parents for developing improved cassava cultivars adapted fromthe populations found in Cote dIvoire.

2 to several agrosystems (Doubi et al., 2016). Thus, cassava is an important plant for food security in the context of climate change and arable land reduction.
Cassava exhibits high morphological variability that reveals intraspecific diversity as perceived by farmers. Furthermore, according to Elias et al. (2001), leaf, stem and tuberous root color remains virtually unaffected by the environment thus allowing for distinction between cultivars. Indeed, farmers distinguish between cultivars based primarily on qualitative traits such as organ color (Lebot et al., 2015). Also, organ color can be used as a marker for genetic characterization in different ecological zones.
In Côte d'Ivoire, this crop represents the second most important food crop after yam (FAO, 2018). However, studies of the in situ genetic diversity held by producers haveyet been to be conducted. Yet, study cultivar morphological diversity is essential for developing new varieties adapted to different agro-ecological zones for subsequentadoption by producers. The objective of this work is to evaluate the morphological diversity of cassava on the basis of qualitative characteristics. Specifically, the aimswere to (i) analyze morphological variability, (ii) establish the genetic structure of cassava accessions originating from Côte d'Ivoire and (iii) identify the most widespread cultivars in order to include them in cassava genetic improvement programs.

Study area
Côte d'Ivoire has a topographythat has few contrasting features overall. However, three main sub-topographies can be distinguished. These are the plains that extend to the south of the country, the plateaus that extend the plains to the north and the mountainous massifs located in the west of the country (Avit, 1999).
As for the vegetation of Côte d'Ivoire, it is divided into two large parts: the Guinean domain and the Sudanese domain. The Sudanese domain, located in the northern part of the country, is characterized by savannah. This area is under the influence of the Sudanese climate, which corresponds to a tropical climate with an average annual rainfall of between 1200 and 1600 mm. The Guinean domain, characterized by the forest zone, is located in the southern half of the country and is under the influence of three climates. These are the sub-equatorial climate, the humid tropical climate and the mountain climate. The sub-equatorial climate or 'Attiéen climate', includes the coastline and a large part of the forest area with an annual rainfall of between 1200 and 2200 mm. The humid equatorial climate or 'Baouléen' climate with 1000 to 1900 mm of rainfall per year extends from the east (Bouna and Bondoukou regions) to the forest and mountainous regions of the west, passing through the center of Côte d'Ivoire (Bouaké region). The mountainous climate is located in the mountainous massif of western Côte d'Ivoire in the regions of Man, Toulepleu and Danané, with an average annual rainfall of between 1600 and 2000 mm (Goula et al., 2007).

Plant Material
The plant material consists of 180 cassava cultivars from 13 regions of Côte d'Ivoire. Figure 1 shows the different localities surveyed.

Frequency of qualitative traits
The variability of the 14 qualitative traits studied was assessed by determining the frequency of occurrence (Pi) of phenotypes of each trait. These relative frequencies were used to determine the mode of each trait.

Statistical analysis of the data
A Multiple Correspondence Analysis (MCA) was used to reveal the most discriminating traits and the relationships between traits in a two-dimensional space. Hierarchical Ascending Classification (HAC) was performed using Ward's method to highlight homogeneous groups and duplicates. Descriptive statistics, MCA and HAC were performed using STATISTICA software version 7.1 (StatSoft Inc., France). Histograms were generated with Excel 2010 software.

Descriptive analysis of local cultivars
Analysis of phenotypic frequencies of traits revealed significant variability within each trait ( Figure 2). However, low variability was noted in the characters tuberous root-pulp color, tuberous-root epidermis color and leaf-lobe shape. Indeed, more than 90% of the accessions evaluated showed white root pulp, brown-skinned root and broad leaves. Accessions with yellow pulp, white-skinned tubers, and thin-lobed leaves represented less than 10% of all accessions. The number of cultivars with green immature leaves was approximately equal to those with purple immature leaves. In addition, nearly half of the cultivars had red petiole leaves, pink phelloderma tuberous-root, and bicolored (green-red) immature stems. Regarding the taste of tuberous root-pulp, 73% were sweet versus 27% bitter.

4
In addition, nearly ¾ of the local cultivars flowered and showed leaves with dark green coloration. Furthermore, in 66% of the local cultivars, the leaf veins were bi-colored (red-green) and the stem cortex was dark green in color.

Relevance of morphological descriptors
The MCA highlighted the traits that best explained variability among cassava cultivars. The first five factorial axes accounted for 52.73% of the variation (Table 1). Also, based on the contributions of each trait to the formation of the first five factorial axes, 10 out of 14 traits best explained morphological variation ( Table 2). The first five factorial axes are defined as follows: Axis 1 was defined by the characters petiole coloration, young stem and the character tuberous root taste. It explained 18.19% of the total variation. The characters petiole color and tuberous root taste were negatively correlated with this axis. On the other hand, the character color of the young stem was positively correlated to it ( Figure 3). Thus, axis 1 pitted cultivars with red leaf petiole and bitter taste of tuberous-root against those with green immature stem.
Axis 2 explained 10.35% of the total variability (Table 1). It is characterized by leaf-lobe shape, mature stem coloration, immature stem coloration, phelloderma tuberous-root coloration and stem cortex coloration (Table 2). This axis pitted cultivars with reddish immature stem, blackish mature stem, and narrow leaves against cultivars with white phelloderma tuberous-root and light green stem cortex ( Figure 3).
Axis 3 explained 9.54% of the total variability ( Table 1). The traits petiole color, epidermis tuberous-root color, phelloderma tuberous root color, and stem color contributed to this component ( Table 2). Axis 3 pitted cultivars with green-dominant bicolored petioles against cultivars with tuberous roots with white epidermis and phelloderma, reddominant bicolored leaf petiole, and gray-colored mature stems ( Figure 4).
Axis 4 accounts for 8.07% of total cultivar variability ( Table 1). The characters that contributed to its formation are: the color of the mature leaf, petiole, apical stem and phelloderma of tuberous roots (Table 2). This axis contrasts cultivars with a light-green leaf and cultivars with a bicolored (red-green) leaf petiole with red dominance, a red apical stem and a white phelloderma ( Figure 5).
Axis 5 is characterized by leaf petiole color, mature stem color, stem habit ( Table 2). On this axis, cultivars with a dichotomous habit are opposed to those with green leaf petiole, yellowish mature stem and a trichotomous habit ( Figure 6). Axis 5 explains 6.58% of the total variability of the cultivars (Table 1).   Group 4 with 10.56% of the cultivars contained the bitter cultivars with tuberous roots possessing a brown epidermis, white pulp, young bicolored stems, and leaves with bicolored veins and red petioles. Cultivars in this group also had tuberous roots with a yellowish phelloderma and stems with a dark-green cortex.

Identification of duplicates within cassava accessions
The traits studied allowed for the distinction between local cassava cultivars. The Euclidean distance matrix was used to identify duplicates within each cultivar group. Indeed, accessions with different names and a zero Euclidean distance were considered as identical cultivars. Thus, the cultivars Blannin, Déhikachia, Six Mois, Egypt and Sanka are duplicates. In addition, the cultivars Blêbou, Israël and Agbabalama on the one hand, and the cultivars Totocla, Clapkan, Trogla, Gnananmininan and Kalowôrô on the other, would be duplicates (Table 3). In the end, of the 180 cassava cultivars, 131 distinct cultivars and duplicates accounted for 27.22%. In addition, cultivars recorded under the same name of Yacé in different areas were effectively identical for all traits. In contrast, Bonoua and Anader designated different cultivars because they exhibited different characters. In analyzing the distribution of cultivars, Yacé was the most common, followed by Trogla, Six Mois and Blêbou (Table 3).

Discussion:-
Morphological characterization of plant material is the preliminary phase of any plant breeding program. In this study, in situ morphological variability assessment missions were carried out in Côte d'Ivoire, using qualitative markers to identify the most-cultivated cassava cultivars. Indeed, according to Elias et al. (2001), qualitative traits such as organ color, leaves, stem and roots in cassava are highly heritable and are good markers that help discriminate between cultivars.
This study indicated significant variability in quality traits among the different local cassava cultivars encountered. However, the analysis revealed that the majority of cultivars exhibited tuberous roots with a brown epidermis and broad-lobed leaves. These results are similar to those of Lebot et al. (2015) in and French Guiana (Elias et al., 2000). On the other hand, nomenclature could also explain this level of duplication. Indeed, in peasant nomenclature, several names can be assigned to the same cultivar depending on the region and ethnicity (Elias et al., 2001). Thus, the cultivar named Totocla by the Baoulé in the center is called Clapkan by the Wobé in the West, Kalowôrô by the Koulango in the Northeast, Gnananmininan by the Malinké in the Northwest, and Trogla by the Gouro in the Centre-West. The cultivar Six mois is so named in the South, but Egypt in Adiaké, Blannin in Gohitafla, Déhikachia in Fakobly and Sanka in Abengourou. Also, the cultivar called Blêbou in the Center-West is named Israel in the South-East and Agbabalama in the North-East. On the other hand, the cultivar Yacé was given the same name in different regions. This study showed that the most widespread cultivars are Yacé, Trogla, Six mois and Blêbou. However, the Trogla cultivar, although widespread, is not widely cultivated because of its very bitter taste, probably due to a very high level of cyanide in the pulp. Indeed, this study shows that people in Côte d'Ivoire prefer sweet cassava cultivars.

Conclusion:-
This study focused on the morphological diversity of local cassava cultivars in Côte d'Ivoire. This description highlighted the morphological diversity that exists within the cassava cultivars held by farmers. This diversity is best explained by 10 of the 14 characters used. The local cassava cultivars are subdivided into five different morphological groups. Four local cassava cultivars were identified as the most widespread: Yacé, Six mois, Blêbou and Trogla. In addition, the study showed that diversity is not geographically structured. There would therefore be a 12 significant flow of genes favored by farmers, which would prove their role in preserving and maintaining genetic diversity in situ. The sustainable management of the resources of this crop depends on the farmers.