Morphological diversity of taro genus Xanthosoma collected in four geographical areas in Côte d’Ivoire based on qualitative traits

This study is part of the context of the development and sustainable management of neglected plant genetic resources in Côte d'Ivoire, including taro. The objective is to characterize the morphological diversity within taro accessions of the genus Xanthosoma from four geographical areas of Côte d'Ivoire. The study took place in the central, eastern, western and southern geographical areas of Côte d'Ivoire, involving 119 accessions of taro genus Xanthosoma comprising four morphotypes (M1, M2, M3 and M7). These accessions have been characterized based on traits related to the plant's habit, leaves, main tuber and secondary tubers, revealing a considerable morphological diversity. The observed traits were highly discriminating, leading to the identification of four homogeneous classes. The morphotypes M1, M2, M3 and M7 played a crucial role in classifying the 119 accessions of the taro genus Xanthosoma , with each class exclusively containing one of the four morphotypes. Classes 1 and 2, containing the M2 and M1 morphotypes, respectively, were closely related. These results demonstrate that the majority of taro accessions in Côte d'Ivoire can be characterized by the presence of four morphotypes: M1, M2, M3 and M7. Taro breeding efforts could be directed based on these four Xanthosoma morphotypes.


INTRODUCTION
Taro holds significant importance as a staple food in numerous African countries, particularly south of the Sahara, contributing to food security as a reserve food source.Cultivated for its tubers and consumed for its leaves, two common taro genera in sub-Saharan Africa are Colocasia and Xanthosoma (Onyeka, 2014).Both genera are well-suited to various geographical areas in sub-Saharan Africa and rank among the most widely consumed tuber plants alongside cassava and yam.In West Africa, Xanthosoma is recognized as the true taro, serving as the primary edible Araceae (Opara, 2003).In Côte d'Ivoire, tuber crops, including taro, hold a significant place in the dietary habits of the population, alongside cassava and yam, forming the foundation of the diet in the 1960s (Haeringer, 1972).Despite its nutritional value, taro is relatively less known and valued compared to yam and cassava.
Taro's dry matter primarily consists of 60 to 90% carbohydrates, with starch content ranging between 73 and 80%, including an amylose content between 19 and 30.62% (Jane et al., 1992;Pérez et al., 2005).Notably, taro is richer in amylose compared to cassava (16.89%) or maize (22.4%) (Liu et al., 1997).With a digestibility estimated at 98.8% (Varin and Vernier, 1994), taro tubers are utilized in the production of various food products, including flour (Amon et al., 2011(Amon et al., , 2014;;Mulyaningsih et al., 2019).Despite its nutritional richness and potential as a food and cash crop, taro is often considered a secondchoice food in Africa, particularly in Côte d'Ivoire.Consequently, the cultivation system for taro in Côte d'Ivoire remains underdeveloped, and its agronomic potential is not well-explored.Adequate documentation of local resources, their variability, and distribution is lacking, yet such data is crucial for defining effective management and improvement strategies for taro consumption in Côte d'Ivoire.In a recent study conducted in Côte d'Ivoire, Koffi and Koffi (2021) identified and described seven taro morphotypes (M1, M2, M3, M4, M5, M6 and M7) based on farmers' knowledge.Subsequently, taro accessions containing the seven morphotypes were re-examined by Koffi et al. (2021) to determine the botanical genera of taro cultivated in Côte d'Ivoire.These authors identified two genera of taro in cultivation : Colocasia and Xanthosoma, based on qualitative characteristics of the leaves.To formulate an effective strategy for taro improvement in Côte d'Ivoire, understanding the genetic variability of the genera Colocasia and Xanthosoma is essential.The objective of the study is to characterize the morphological diversity within taro accessions of the genus Xanthosoma from four geographical areas of Côte d'Ivoire.

Plant material
The plant material utilized in this study comprises 119 taros accessions collected from the central, eastern, western and southern geographical areas of Côte d'Ivoire.These accessions pertain to four of the seven morphotypes (M1, M2, M3 and M7) of taro identified in Côte d'Ivoire by Koffi and Koffi (2021).Subsequently, Koffi et al. (2021) described and identified these morphotypes as belonging to the genus Xanthosoma (Table 1).

Study site
The trials to assess the morphological diversity of taro accessions belonging to the genus Xanthosoma were conducted from June 2020 to March 2021 in the commune of Soubré.The geographical coordinates of the site are 5° 42' 81″ north latitude and 6° 33′ 12″ west longitude.Soubré experiences a humid equatorial climate with an average temperature of 27°C.The annual variations in precipitation and temperature result in two rainy seasons and two dry seasons.The significant dry season extends from December to March, followed by a rainy season from April to mid-July.Subsequently, there is a dry season from mid-July to mid-September, concluding with a brief rainy season from mid-September to November.Soubré's vegetation is characterized by a dense humid forest, and the soil is predominantly deep ferritic with a sandy-clay texture and a lumpy structure (Yao-Kouamé and Kané, 2008).

Experiment design
The field layout followed a completely randomized design with five replications.The experimental plot measured 26 × 26 m and included 595 plants, representing the 119 accessions.Each accession was represented by 5 plants.The planting distance was set at 1 m between and within rows, with 1 m edges.Manual weeding was performed throughout the plant development phase.

Data collection and analysis
Twelve qualitative traits, selected from standard descriptors for Taro (IPGRI, 1999), were employed to characterize morphological diversity (Table 2).The collected data underwent Multiple Correspondence Analysis (MCA), Hierarchical Ascending Classification (HAC), and Discriminant Factor Analysis (DFA).Multiple Correspondence Analysis (MCA) was utilized to explore relationships between the qualitative traits and further describe morphological variation among accessions.MCA is particularly valuable for describing datasets by combining correlated variables into factors.
Hierarchical Ascending Classification (HAC) was employed to derive homogeneous groups of accessions.Lastly, Discriminant Factor Analysis (DFA) was conducted to identify the most discriminating traits and elucidate the characteristics of the groups obtained through HAC.All these analyses were carried out using the statistical software R version 4.1.0(R Core Team, 2021).

Morphological variability and diversity structuring of 119 taro accessions of the genus Xanthosoma
Following the elbow detection rule, which identifies the breakpoint of the decay curve of the percentages of variance explained by the principal components of the MCA (Cattell and Vogelmann, 1977), the first three principal components located before the elbow were retained for the interpretation of the results (Figure 1).These components collectively explain 66.97% of the total variation.
With the exception of buds color (BuCo), all 12 observed traits were relevant in structuring the diversity of taro accessions belonging to the genus Xanthosoma.The shape of the base of the leaf (ShBL), predominant position of the leaf blade surface (PrPL), color of the main rib (CoMR), rejection formation (ReFo), and color of the flesh of the main tuber (CoFM) significantly contributed to the formation of axis 1 (r2 > 0.7).
Additionally, color of the outer sheath (CoOS) and color of the inner sheath (CoIS) made a significant contribution to the formation of axis 2 (r2 > 0.7), while color of the flesh of the secondary tuber (CoFS) strongly contributed to the formation of axis 3 (r2 > 0.7).Blade color (CoLB) and petiole color (CoPe) were more involved in the formation of axes 1 and 2 (r2 > 0.7).Moreover, color of the petiole base (CoPB) and color of the flesh of the main tuber (CoFM) had significant impacts on the formation of axes 1 and 3 (r2 > 0.7).
Each factorial axis of MCA was named based on the contribution of different variables to its formation (Table 3).Therefore, axis 1 describes leaf structure and characteristics of the shoots and plants, axis 2 describes the coloration of the aerial part, and axis 3 mainly describes the coloration of the tuber flesh.The projection of taro accessions of the genus Xanthosoma in the factorial planes 1 to 2 of MCA took into account axis 1 (32.10%) and axis 2 (21.60%), expressing the greatest variability.It revealed three distinct groups (Figure 2).
In Figure 3, the projection of variants in the factorial plane planes 1 to 2 of MCA revealed that Group 1 was composed of accessions with the following traits: Greendark leaf blade (LBGD), main rib of yellow color (MRYe), green-white petiole (PeGW), pink-white buds (CoPW), sagittate base leaf (BLSa), sheaths purple on the outside (OSPu), and brown inside (ISBr), pink petiole base (PBPi), main tuber with pink (FMPi) or beige (FMBe) flesh.Some of these accessions had secondary tubers showing yellow (FSYe), pink (FSPi), or white (FSWh) flesh.Other accessions in this group had secondary tubers with a doublé pink and white flesh color, either pink-dominant (FSPW) or white (FSWP).Group 2 comprised accessions with the leaf blade (LBGP), petiole (PeGP), and the outside sheath (OSGP) of pale green color.The inside of the sheath of these accessions was green (ISGr).
Group 3 was composed of accessions with rejections (FoYe), main rib either green (MRGr) or yellow-green (MRYG), horizontal leaf blade surface (predominant position) (PLHo), and flesh of the secondary tubers with a doublé beige and pink color, with beige dominance (FSBP).

Classification of the 119 taro accessions of the genus Xanthosoma into homogeneous classes
Taro accessions of the genus Xanthosoma were distributed into four homogeneous classes by the Hierarchical Ascending Classification (Figure 4).
Class 1 comprised only M2 morphotype accessions from the central, eastern, western, and southern areas.Class 2 gathered accessions of morphotype M1 originating from the central, eastern, western and southern areas.Class 3 exclusively contained accessions of morphotype M3 from the eastern and southern areas.Lastly, Class 4 included only accessions of morphotype M7 from the eastern area (Table 4).The area of origin of taro accessions of the genus Xanthosoma does not appear to be a determining factor in their classification.Conversely, the morphological type seems to be the primary factor differentiating these classes.
Although the Multiple Correspondence Analysis structured the 119 accessions of the genus Xanthosoma into three groups (Figure 2); the Hierarchical Ascending Classification revealed four homogeneous classes.One of the MCA groups would thus contain two very similar morphotypes with many similarities and few differences.

Discrimination of homogeneous classes of the 119 taro accessions of the genus Xanthosoma
The projection of the four classes of taro accessions belonging to the genus Xanthosoma into the Discriminant Factorial Analysis factorial plane resulted in a highly distinct structuring (Figure 5).Despite accessions in classes 1 and 2 belonging to different morphotypes, these classes were found to be very close to each other, originating from group 1 obtained by the structuring of the MCA.Conversely, classes 3 and 4 come respectively from groups 2 and 3 of the MCA (Figure 2).
The frequencies of accessions having the said variants within each class, the characteristics of the four homogeneous classes were highlighted.The "global" indicator presented the frequencies of the variants within the 119 taro accessions of the genus Xanthosoma.
Class 4 gathered accessions with light-pink petiole base (CoBP=Light-pink), green petiole (CoPe=Green), green leaf blade (CoLB=Green), hastate leaves (ShBL=Hastate), pink-beige flesh of the main tuber (CoFM=Pink-beige), drooping leaf blade (PrPL=Drooping), rejection formation (ReFo=Yes), yellow-green and green main rib (CoMR=Yellow-green, CoMR=Green) and pink buds (BuCo=Pink) (Table 9). Figure 6 shows images of the characteristic variants discriminating the four classes of taro accessions of the genus Xanthosoma.Accessions of the genus Xanthosoma collected across the central, east, west and south areas of Côte d'Ivoire revealed significant diversity.Characteristics related to the plant's habit, leaves, main tuber and secondary tubers proved to be highly discriminating in this study.These traits strongly contributed to the formation of the first three axes in the Multiple Correspondence Analysis, highlighting distinct morphological groups.Taro accessions of the genus Xanthosoma were initially separated into three groups in the factorial planes 1 to 2 of the MCA.Group 1 accessions exhibited greendark leaf blades, whitish-green petioles, a main tuber with pink or beige flesh, and secondary tubers with pink, white, and beige flesh.Some of these secondary tubers displayed a doublé coloration of pink-white flesh, either predominantly pink or predominantly white.Group 2 accessions were primarily characterized by the palegreen coloration of the leaf blades and petioles.They also had a main tuber with beige flesh and secondary tubers with white and beige flesh.Group 3 comprised accessions with green leaf blades and petioles, a main tuber, and secondary tubers with flesh of double beigepink color, predominantly pink.These distinctive traits specific to each group confirm the existence of three main types of plants within the taro accessions of the genus Xanthosoma in Côte d'Ivoire.The initial grouping of the 119 accessions into three groups was further refined into four homogeneous classes.Group 1 was subdivided into two classes, resulting in classes 1 and 2. Groups 2 and 3 gaves rise to classes 3 and 4, respectively.These results underscore the substantial agromorphological diversity of taro accessions within the genus Xanthosoma in Côte d'Ivoire.Similar findings were reported by Wada et al. (2021) and Villavicencio et al. (2021) in their studies on the taro species Xanthosoma sagittifolium (L.) Shott.These authors also identified four agromorphological classes within collections of taro accessions belonging to the    blade color, petiole color and color of the flesh tuber.

The analysis of morphological variability in 119 taros
The similarities between the classes of taro accessions belonging to the species X. sagittifolium revealed by Wada et al. (2021) and Villavicencio et al. (2021), and the classes of taro accessions of the genus Xanthosoma observed in our study, suggest that the taro accessions collected in Côte d'Ivoire may contain accessions of the species X. sagittifolium.
However, the rejections formation in the accessions of class 4, a distinguishing feature in this study, was not mentioned by Wada et al. (2021) and Villavicencio et al. (2021).Additionally, accessions of class 4 are atypical, being the only ones that produce a consumable main tuber among the 119 taro accessions of the genus Xanthosoma collected in Côte d'Ivoire.This suggests that the taro accessions considered in this study may encompass accessions of two botanical varieties within the species X. sagittifolium or possibly accessions of a  second species within the same genus in addition to X. sagittifolium.
The morphological types M1, M2, M3 and M7 played a crucial role in the classification of the 119 taro accessions within the genus Xanthosoma.Each class exclusively grouped accessions of a single morphotype, irrespective of their geographical areas of origin.Class 1, for instance, consisted of accessions of morphotype M2 from the central, east, west and south areas.Class 2 gathered only accessions of morphotype M1 from the same regions.Class 3 included accessions of morphotype M3 from the east and south areas, while class 4 contained accessions of morphotype M7 from the east.Classes 1 and 2, representing M2 and M1 morphotypes, respectively, were closely positioned.These two classes, and by extension, these two morphotypes, exhibited many similarities and very few differences.Farmers often found it challenging to differentiate between morphotypes M1 and M2 based on the identical aerial part of the plants, which comprised long petioles and leaf blades.Farmers typically relied on the flesh color of the tuber for distinction, with morphotype M1 producing tubers with generally pink flesh, while morphotype M2 gave tubers with white and beige flesh.Additionally, the coloration of the petiole base below the collar could also be used for differentiation, as morphotype M1 had a pink petiole base, whereas morphotype M2 had a white petiole base.The results strongly suggest that the taro genus Xanthosoma in Côte d'Ivoire exhibits significant morphological diversity.The 119 accessions considered in the study likely belong to the species X. sagittifolium (L.) Schott, as described by Wada et al. (2021) and Villavicencio et al. (2021).The observed polymorphism in the species X. sagittifolium in Côte d'Ivoire could be

Figure 1 .
Figure 1.Decay curve of the percentages (%) of variance explained by the principal components of the multiple correspondence analysis.

Figure 2 .Figure 1 .
Figure 2. Structuring the diversity of 119 taro accessions of the genus Xanthosoma into three distinct groups in the plane formed by the factorial axes 1-2 of MCA.

Figure 2 .
Figure 2. Dendrogram presenting the four homogeneous classes of taro accessions of the genus Xanthosoma highlighted by the hierarchical ascending classification.

Figure 3 .
Figure 3. Projection of the homogeneous classes of taro accessions of the genus Xanthosoma obtained by HCA in the factorial plane 1-2 of the discriminant factorial analysis.

Table 1 .
Number of taro accessions of the genus Xanthosoma collected by morphological type in the center, east, west and south geographical areas, used as plant material.

Table 2 .
List of 12 qualitative variables observed between five and ten months after planting, on five plants per accession for the analysis of morphological diversity of taro accessions of the genus Xanthosoma.

Table 3 .
Eigenvalues, percentagesof variability explained by the factorial axes and MCA and correlations coefficient between traits and the first three factorial axes.
*the strongly correlated traits (r2 > 0.7): ShBL, shape of the base of the leaf; PrPL, predominant position of the leaf blade surface; CoLB, color of the leaf blade; CoMR, color of the main rib; CoPe, color of the petiole; CoPB, color of the petiole base; CoOS, color of the outer sheath; CoIS, color of the inner sheath; ReFo, rejection formation; CoFM, color of the flesh of the main tuber; BuCo, buds color; CoFS, color of the flesh of the secondary tuber.

Table 4 .
Morphotypes, areas of origin and number of homogeneous classes of taro accessions of the genus Xanthosoma.

Table 5 .
Traits observed discriminating the four classes of taro accessions of the genus Xanthosoma highlighted by the discriminant factorial analysis.ShBL, shape of the base of the leaf; PrPL, predominant position of the leaf blade surface; CoLB, color of the leaf blade; CoMR, color of the main rib; CoPe, color of the petiole; CoPB, color of the petiole base; CoOS, color of the outer sheath; CoIS, color of the inner sheath; ReFo, rejection formation; CoFM, color of the flesh of the main tuber; BuCo, buds color; CoFS, color of the flesh of the secondary tuber.

Table 6 .
Variants of characteristic traits of taro accessions of the genus Xanthosoma of class 1 identified by AFD the discriminant factorial analysis., shape of the base of the leaf; PrPL, predominant position of the leaf blade surface; CoLB, color of the leaf blade; CoMR, color of the main rib; CoPe, color of the petiole; CoPB, color of the petiole base; CoOS, color of the outer sheath; CoIS, color of the inner sheath; ReFo, rejection formation; CoFM, color of the flesh of the main tuber; BuCo, buds color; CoFS, color of the flesh of the secondary tuber. ShBL

Table 7 .
Variants of characteristic traits of taro accessions of the genus Xanthosoma of class 2 identified by AFD the discriminant factorial analysis., shape of the base of the leaf; PrPL, predominant position of the leaf blade surface; CoLB, color of the leaf blade; CoMR, color of the main rib; CoPe, color of the petiole; CoPB, color of the petiole base; CoOS, color of the outer sheath; CoIS, color of the inner sheath; ReFo, rejection formation; CoFM, color of the flesh of the main tuber; BuCo, buds color; CoFS, color of the flesh of the secondary tuber. ShBL

Table 8 .
Variants of characteristic traits of taro accessions of the genus Xanthosoma of class 3 identified by AFD the discriminant factorial analysis., color of the leaf blade; CoMR, color of the main rib; CoPe, color of the petiole; CoPB, color of the petiole base; CoOS, color of the outer sheath; CoIS, color of the inner sheath; CoFM, color of the flesh of the main tuber; BuCo, buds color. CoLB