Genetic Diversity and Association of Yield-Related Traits in Taro ( Colocasia esculenta (L.) Schott) Sourced from Different Agroecological Origins of Nigeria

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Introduction
Taro (Colocasia esculenta (L.) Schott) is one of the world's most ancient food crops, with a history of more than 2,000 years in cultivation [1].It originated in south central Asia, while high diversity was reported in Southeast Asia [2].It is morphologically diverse, with over 10,000 landraces worldwide [3], and about 10 ecotypes have been reported growing in Nigeria [4].
Taro is largely produced and consumed in tropical and subtropical countries [5], and Nigeria is the largest taro producer in the world [6].Only the skins of the taro corm and the true anatomical roots have not been reported as food; meanwhile, the corms, blades, petioles, and inforescences are edible.Te corm has been reported to have high starch, while the leaf contains high protein [7].Among tuber crops, taro is perhaps the most widely prepared or processed into more consumable forms [8].It is a staple food, mainly for resource-poor rural dwellers in south eastern Nigeria [4], and is regularly consumed as a main component or as a soup thickener [5].
As is true for some crops, taro remains an orphan, and so far, no improved variety is available in Nigeria.It is chiefy characterized by low productivity, disease susceptibility and poor eating quality [9].Specifcally, taro yield was estimated at 3.94 t ha −1 in Nigeria in 2021, which was very far below the global average yield of 9.50 t ha −1 [6].Yield is a complex trait governed by several genes that govern a number of yield components and are also infuenced by environmental factors, signifying indirect selection breeding to improve taro yield.
Te frst step in any plant breeding program is to identify plants that exhibit variation for the traits of interest.Desirable traits combination should be sought among plants in existing populations such as recommended cultivars, breeding lines and landrace [10].To have a good choice of characters for selection of desirable genotypes, the estimate of heritability, genetic advance, and knowledge of association of component traits with yield is of great importance to plant breeders as it helps them make selection with more precision and accuracy [11].Heritability estimate can be used to predict gain from selection [12].Genetic correlation is a measure of the extent to which the same gene, or closely linked genes, cause simultaneous variation in two diferent traits [13].Path analysis further permits the partitioning of the correlation coefcients into components of direct and indirect factors of association and provides an efective tool in fnding out the direct and indirect contribution of diferent contributing characters towards yield [14].
Many researchers have reported broad-sense heritability and distinguished a number of positive and signifcant associations of yield and yield attributing characters and their direct and indirect efects in diferent root and tuber crops.For instance, in taro [15,16], Tania [15,[17][18][19], sweet potato [20,21], and anchote [22,23], thus, the current study was intended to estimate genetic variability and characters association in taro so as to identify the major traits of importance that could be used as a basis in taro breeding to select superior genotypes.

Description of Site. Te feld trial was carried out at
Ebonyi State University, Department of Crop Production and Landscape Management teaching and experimental feld, Abakaliki, Nigeria, during the rainy seasons of 2018 and 2019.Te site is situated at 06 °4′ N and 08 °65′ E at 55.5 metre above sea level.Te area receives annual rainfall of 1700 to 2000 mm with 80% to 90% relative humidity.Te mean minimum, maximum, and average temperatures were 22 °C, 32 °C, and 28 °C, respectively.Te predominant soil is hydromorphic with moderate to reddish brown silty clay subsoil.Te site is also good for the production of root crops like cassava and yam among the others.

Experimental Design and Trial
Management.Te experiment was laid out using a 10 × 10 simple lattice design with two replicates [24].Each accession was established in a plot size of 5 m 2 consisting of one row of 5 m in length.Te spacing between rows and plants was 1 m and 0.5 m, respectively [25,26].Ten cormels with an average weight of 50 g were used for planting.It was planted on 25 th May, 2018 and 28 th May, 2019.All management practices like weeding and earthing-up were done as recommended during all growth period.

Data Collection.
Data were recorded on 16 quantitative traits from fve randomly taken plants.Te descriptor, code and description of the characters are presented in Table 2. Te traits include number of leaves per plant, plant height (cm), petiole length (cm), leaf length (cm), leaf breadth (cm), leaf area, number of suckers per plant, days to maturity, yield per plant (kg), corm length (cm), corm diameter (cm), cormel diameter (cm), cormel length (cm), corm weight (g), cormel weight (g), and total yield (t ha −1 ).Tese data were recorded following a descriptor of taro developed by the International Board for Plant Genetic Resources [27].Morphological data were recorded at maximum growth stage (120 days after planting), while corm and corm-related traits were recorded at harvest (180 to 220 days after planting).

Data Analysis.
Normality and equal variance test and transformation of data for some characters were done using Minitab software [28].Descriptive statistics were used to depict variations that emerge from quantitative traits.Quantitative traits were subjected to multienvironment trail analysis (META) based on simple lattice design in order to verify diferences among accessions.Phenotypic and genotypic variances and coefcient of variations were estimated as per the procedure suggested by [29].Broad sense heritability (h 2 B ) was estimated using the formula suggested by [30].Genetic advance (GA) at selection intensity (K) of 10% was calculated by the formula suggested by [31].Genetic advance as percentage of mean (GAM) was computed to compare the extent of predicted genetic advance of different characters under selection.Genotypic and phenotypic correlation components between traits were estimated using the equation suggested by [32].For path analysis, yield per plant was taken as a dependent variable, while others were considered independent variables.Direct and indirect efect of independent variables on yield per plant was estimated using formula suggested by [14].Correlation analysis was carried out using META R [33], while path analysis was done using Excel.4) showed a highly signifcant (P ≤ 0.01) diferences among the studied accessions for all traits except cormel length which showed signifcant (P < 0.05), while accessions did not difer statistically signifcantly for corm diameter.

Performance of Genotypes.
Te estimate of range and pooled mean performance of accessions for total yield and yield related traits are presented in Table 3. Yield performance of taro accessions ranged from 1.25 t ha −1 to 18.03 t ha −1 with  1).Number of leaves per plant ranged from 7.40 to 12.40 with pooled mean of 9.63.Plant height ranged from 35 cm to 110 cm with a mean of 75.28 cm.Petiole length ranged from 16.67 cm to 69.00 cm with mean of 31.82 cm.Leaf length ranged from 5.00 cm to 72.00 cm with a mean of 47.31 cm.Leaf breadth ranged from 16.50 cm to 56.40 cm with a mean of 35.86 cm.Number of suckers per plant ranged from one to 14.40 with a mean of 7.76.Days to maturity ranged from 178 to 213 days with a mean of 197 days.Yield per plant ranged from 0.05 kg to 1.16 kg with a mean of 0.67 kg.Corm length ranged from 2.26 cm to 9.36 cm with a mean of 6.70 cm.Corm diameter ranged from 2.62 cm to 11.06 cm with a mean of 6.74 cm.Cormel length ranged from 3.40 cm to 8.38 cm with a mean of 5.78 cm while cormel diameter ranged from 2.45 cm to 5.95 cm with a mean of 3.71 cm.Corm weight ranged from 0.04 kg to 0.39 kg with a mean of 0.17 kg.Cormel weight ranged from 16.21 g to 84.30 g with a mean of 39.71 g.Phenotypic coefcient of variation (PCV) and genotypic coefcient of variation (GCV) values for all traits studied among taro accessions are presented in Table 3.A high percentage of PCV was observed for leaf area (80.67%), followed by corm weight (58.82%), total yield (28.25%), yield per plant (21.11%), and number of suckers per plant (20.66%).Moderate PCV was noted for cormel weight (17.05%), corm diameter (15.56%), petiole length (13.49%), corm length (12.58%), plant height (11.91%), leaf length (11.835%), and leaf breadth (10.663%).Te remaining traits showed low PCV.Likewise, a high percentage of GCV were observed for leaf area (76.923%), followed by corm weight (58.824%), total yield (24.118%), and yield per plant (21.108%).Moderate percentage of GCV was noted for the number of suckers per plant (16.950%), yield per plant (14.925%), corm diameter (14.613%), corm length (11.268%), and plant height (10.011%), while other traits showed a low percentage of GCV.

Discussion
4.1.Variability in Quantitative Traits.META combined over seasons in the current study showed highly signifcant (P ≤ 0.01) diferences among the tested accessions for most traits (Table 3).Tese signifcant variations among tested taro accessions for the characters showed the existence of variability to have an efective selection.Te variation observed for measured quantitative traits in this study were in agreement with the earlier fndings of some researchers [34,35] who had reported high variability for same traits among 14 taro genotypes studied in India.
PCV and GCV values are considered as high if they are ≥20%, medium 10-20%, and low ≤10% [36].Te present study showed higher PCV than GCV estimates for all characters (Table 5) indicating existence of variability among accessions for the characters studied.Besides, PCV and GCV in this study were close to one another for most characters indicating the environmental efects are small.Higher genotypic variances and coefcients of variation for most of the characters than their corresponding environmental variances are also indicative of the existence of variation at the genotypic level.Te present work is in line with the work [34] that reported higher PCV than GCV among 14 taro genotypes studied in Ethiopia [37] and India [38].

Heritability and Genetic Advance in Quantitative Traits.
Estimate of genetic advance is more useful as a selection tool when considered jointly with high genotypic coefcients of variation and high heritability values [39].In this study, high heritability values with high genetic advance as a percentage of the mean (>10%) were observed for corm weight and leaf area indicating these characters are principally under genetic control (due to the high additive gene efect) and selection for these traits can be achieved through their phenotypic performance.For traits with a high heritability value but a moderate value of genetic advance (such as corm length) careful selection is needed.Similarly, characters with high heritability values but a low value of genetic advance (i.e., number of leaves per plant) may be governed by nonadditive gene action or a high genotype by environmental interaction and used for the development of hybrid varieties.Lower heritability values and GAM (%) implies most of the variations for these traits were environmental, and such traits require more management practice than selection to improve the traits performance.Similar work was reported by many researchers on diferent crop plants [15,22,34,[37][38][39][40][41][42].

Associations in Quantitative
Traits.In the present study, most traits had a higher genotypic correlation coefcient than phenotypic correlation indicating the association among characters was largely due to genetic variance and the reverse is because of environmental variance [43].Besides, most characters showed a positive correlation both at the genotypic and phenotypic level with yield per plant.Te positive and signifcant association might be due to the efect of genes, a result of the presence of strong coupling linkage between their genes, or the character may be the result of pleiotropic genes that could control these characters in the same direction [44].Yet again, from this fnding some characters showed negative and signifcant association among each other.Such negative correlation might be because of the fact that diferent genes or pleiotropic genes that have dominance on the character may control the character in diferent direction [44].Yield per plant was positively and signifcantly (P < 0.01) correlated with most traits indicating these traits are useful for indirectly selecting high-yielding varieties, as selection for yield per se is not efective because of the complex nature of the trait.Te present fnding is in line with the work [45] that reported a similar scenario.International Journal of Agronomy 4.4.Direct Efects of Characters on Yield.Plant height, leaf area, corm weight, and cormel weight exerted a positive direct efect on yield per plant.Tese characters also observed a strong, positive, and highly signifcant genotypic correlation with yield per plant.Te high correlation coefcient of these characters with yield per plant was largely due to the direct efect.As the direct efect and genotypic correlation between the two traits are positive, it indicates a true relationship.Te cause and efect relationships are the products of interacting characters infuencing each other [11].In line with this fnding, many researchers reported the same among taro [45,46] and Tania [15,45,46].

. Conclusion
Tis study assessed the phenotypic variability of 100 taro accessions collected from fve states of Nigeria.Te analysis of variance revealed the existence of phenotypic variability among the studied accessions.High genotypic coefcient of variation, heritability, and genetic advance were observed for leaf area, corm diameter, plant height and corm weight.Te result of the genotypic correlation coefcient as proved by path analysis also showed plant height, leaf area, corm, and cormel weight have a positive and signifcant direct efect on yield per plant.Tus, it can be concluded that these characters exert a high positive direct efect on yield t at the genotypic level and hold the highest merits to be selected in breeding programs towards improving yield in taro.Te presence of morphological variation between genotypes will give opportunity for studying the accessions at the molecular level and searching of functional alleles that could be used in marker-assisted selection.
Quantitative Traits among Taro Accessions.

Table 1 :
List of taro landraces used in the study.
a pooled mean of 10.08 t ha −1 .Sixty percent of the total accessions gave yield above pooled mean yield (10.08 t ha −1 ).(EBNFC084 and EBNFC100) from Abia, two (EBNFC 032 and EBNFC037) from Anambra, and one (EBNFC075) from Imo state (Table

Table 2 :
Quantitative descriptors for agromorphological characterization of taro accessions.
4LPP: number of leaves per plant, PHt: plant height (cm), PL: petiole length (cm), NSPP: number of suckers per plant, MD: days to maturity, YPP: yield per plant (kg), CRW: cormel weight (g) and total yield (tons/ha), leaf length, leaf breadth, leaf area, corm length, corm diameter, cormel length, and cormel diameter.4InternationalJournal of Agronomy 3.3.Estimation of Variability.Genotypic and phenotypic variance of all traits studied among taro accessions are presented in Table 5. Genotypic and phenotypic variance ranged from 0.001 to 56.79 and 0.001 to 80.39, respectively.High phenotypic variance values were noted for plant height (80.39), cormel weight (45.83), leaf length (31.11) petiole length (18.42), and days to maturity (41.98).Whereas, high genotypic variance value 56.79, 25.73, 21.84, and 20.31 were noted for plant height, days to maturity, leaf length, and cormel weight, respectively.Te lowest genotypic and phenotypic variance were noted for leaf area, yield per plant and corm weight.