Sixty yam accessions from ten different geographic origins of Southern Nations Nationalities and People’s Regional State and Oromiya region of the country were used for this study. The sprouted tubers of some accessions were obtained from Research Centers whereas others were directly collected from farmers’ fields during early March, 2010 as indicated in Table 1. The samples collected were planted on April 2010 in complete randomized block design with three replication at two research sites (namely at Hawassa and Wonago) which are found under South Agricultural Research Institute at the end of April 2010 as indicated in Figure 1. All important cultural practices such as staking, weeding and irrigation were done starting from planting till harvesting.

Among 45 morphological characters (Table 3) observed in the study presence and absence of spines on stems and roots, number of male and female inflorescence, stem length, twining direction, and flesh color were the major traits considered for species identification. The species identification was done through observing some earlier developed identification keys [7].

The identified Dioscorea species were subjected to qualitative morphological characterization. The qualitative morphological characterizations were carried out to determine the level of variability and the relationship among accessions using IPGRI/IITA descriptors [8]. Characters were observed for five different healthy plants per accession. The color aspect of the plant was recorded using Munsell color chart for plant tissues. The farmers perception were taken at the time of collection and sensory evaluation during harvesting for both boiled (eight characters) and un-boiled yam tubers.

The total forty five morphological characters were recorded at the time of young, flowering, maturity stage of the plant and at the time of harvesting using IPGR descriptor list [8] (Table 2 and Table 3). The collected raw data were subjected to statistical analysis using computer software packages for the diversity and relatedness study among yams (Dioscorea spp.).

Fifteen farmers were selected from Gedio zone (Wonago district) near the research site. Following their consent an introduction was given to them by the researcher on the sensory parameters of interest. Yam tubers from each accession were taken washed and boiled by farmers as their method of preparation. The sensory values decided by farmers were recorded by the researcher as indicated in Table 3 using IPGRI descriptor list.

Statistical analysis was done using Numerical Taxonomy and Multivariate Analysis System Version 2.02 NTSYpc software program [9] and the data reduction function of SPSS for windows (version 12.0, 2003). The standardized data for qualitative characters were subjected to multivariate analysis and principal component analysis to identify the most discriminating morphological characters. The matrix of similarity was generated based on distance coeficents. The distance matrix was subjected to hierarchical cluster analysis using Shan through an un-weighted pair group method average (UPGMA) [10]. Cophenetic value (ultrametric) matrix was used to compute the cophenetic correlation as a measure of goodness of fit.

Based on presence and absence of spines on stems and roots, number of male and female inflorescence, stem length, twining direction, and flesh color sixty yam germplams from ten major growing areas of the country were grouped into six species namely D. alata, D. bulbifera, D. abyssinica, D. praehensilis, D. rotundata and D. cayenensis. The two species D. rotundata and D. cayenensis were observed to have 1 - 3 male inflorescences per spike and after cutting revealed white and yelowish flesh color. During this study the yellowish colour was grouped to D. cayenensis whereas the white flesh colour was grouped to D. rotundata as indicated in Figure 2(b) and Figure 2(d) respectively.

The species D. alata was differentiated from other groups based on its four angled stem. The average stem length of this species under study were 10 m long, it had different tuber shape apperance (Figure 2(f)). Whereas D. abyssinica had an average climber stem of 2 - 5 m and the number of male infloresences observed was 3 - 6. Under this study most of the D. abyssinica species had male infloresecence (Figure 2(a)). Spines were observed on stem of this species. Whereas, the average stem length recorded from D. praehensilis was 10 m and spines were observed both on roots and stems of this species. The number of male and female inflorescences observed in D. praehensilis was 3 - 5 and 1 - 2 respectively (Figure 2(e)). Generaly D. abyssinica and D. praehensilis revealed three types of flesh color which were purplish colour, a central white colour surrounded by purplish colour and the mixure of white and purplish colours (Figure 2(a) and Figure 2(e)).

The species whose stem was climbing to the left or in a clock wise direction was grouped in to D. bulbifera (Figure 2 (c)). The average stem length of this species was 3 - 10 m with 3 - 5 male inflorescence. Its areal tuber showed both white and purple color. While, all the other species under study twining direction was anti clock wise.

Among 45 qualitative morphological characters recorded on six Dioscorea species namely D. abyssinica, D. praeihensilis, D. cayenensis, D. rotundata, D. alata and D. bulbifera 12 traits did not reveal phenotypic variation among the 60 yam germplasm studied. These traits were not included for clustering and principal component analysis. Based on the relative magnitude of distance similarity matrix and dendrogram using Shan UPGMA cluster analysis, all sixty yam genotypes included in the study were grouped into five clusters (Figure 3).

At the similarity distance 1.81, the dendrogram identified three clusters 1 and 2 which contain eight to eighteen accessions per cluster (Table 4 and Table 5). Cluster 1 is the second largest group and contains 18 yam accessions with green mature petiole colour. Cluster 2 contained accessions with pale purple young petiole colour, green mature petiole colour, high leaf density, presence of cracks on tuber surface, intermediate corm size, highly coloured tuber after cooking and cooked tuber sweetness.

The dendrogram at the similarity distance 1.6 identified clusters 3. This cluster group is characterized by dark brown stem color after emergency, green mature petiole color, intermediate corm size and presence of cracks on the cooked tuber.

The dendrogram with similarity distance 1.71 identifies one cluster group 4. This cluster is the largest and composed of 19 accessions. This group is characterized

by yellow mature petiole color, green stem color and absence of cracks on the tuber. Cluster 5 contained two cluster groups cluster 5a and cluster 5b. Cluster 5a is a group of D. bulbifera species with yellow mature petiole color and green stem color. Cluster 5b is a group of D. rotundata composed from three yam accessions. This group is characterized by absence of barky patches on the stem, green stem color, and yellow mature petiole color, small tuber width at middle part, absence of tuber cracks, late maturity group and white tuber color after cooking. In this analysis the cophenetic correlation coefficient result was r = 80 which revealed the efficiency of the dendrogram.

Note: Ji-Jima, Ga-Gamogofa, , Da-Dauro, Wo-Wolayita, Si-Sidama, Ar-Areka, Km-Kembata, Ge-Gedio, Wg-Wolega, Kf-Kefa.

The PCA results revealed that the first axis largely accounted for the variation among yam accessions (24.87%) followed by the second axis (14.96%) and third axis (11.63%). The first five axes with eighteen values greater than unity accounted for the total variations among 33 characters describing 69.31% and the first three axes accounted for 51.48% (Table 6 and Table 7). Traits with comparatively greater weight in PC1 and PC3 were young petiole color. Correspondingly greater weight in PC2 was color of tuber after cooking. Similarly, flesh color at the lower part of tuber and flavor of cooked tuber resulted in larger weight in the first three principal components while tendency of tuber to branch gave greater weight to the first two principal components.

Note: SN = Serial number.

Note: SN = Serial number; *Bolded values revealed highly correlated morphological traits to respective principal components.