Results obtained showed that 2 individual seeds of the accession TDr-893x903 took the shortest number of days to sprout, while 4 individual seeds of TDr-3010 took the longest number of days to sprout (Fig. 1). However, out of the 10 seeds planted per accession, 40%, 70% and 70% of TDr-893x903, TDr-3010 and TDr-98/917, respectively sprouted. This shows a higher seed viability rate in TDr-3010 and TDr-98/917 accessions, but they required longer time to break dormancy relative to TDr-893x903. There are dearth of information on the cultivation of yam using the zygotic seeds as propagule, except few reports on its usage in vitro in the generation of callus for propagation through somatic embryogenesis techniques (Manahoran et al., 2016). Since, there is lack of information on the viability of the zygotic seeds, the planting substrate becomes inconsequential in terms of its effect on the seeds viability. However, in this research, soil constraints are being circumvented in using sterile cocopeat substrate in hydroponics system (Ossai et al., 2020).
The plants grew steadily as they grow older. At 8 weeks after planting, the plant height ranged from 15.1 cm (TDr-98/917-7) to 22.0 cm (TDr-3010-1) (Fig. 2). Among the individual seeds in the three accessions, TDr-3010-1 grew taller than the rest individual plants. As the plants grew older, the number of leaves produced increased with a range of 5 (TDr-3010-3) to 20 (TDr-893x903-1) at 8 weeks old (Fig. 3). Expectedly, production of leaves within the vegetative stage of plants development is essential for their photosynthetic activities and food production. However, in this case, the tallest plants did not produce the highest number of leaves, which shows longer internode in the individual plant. Also, when compared to planting yam with the tuber part as seed, higher growth rate and leave production has been reported within 8 weeks interval than what was achieved using the zygotic seed, despite sprouting approximately same time interval (2–4 weeks) (Aighewi et al., 2020).
There were varied sizes and number of tubers produced by the individual zygotic seeds of the three accessions. Only TDr-893x903-1, TDr-98/917-1 and 2, and TDr-3010-1 produced 2 tubers each, while the rest individual plants produced 1 tuber each. The tuber sizes ranged from 2.3 (TDr-3010-2) to 24 (TDr-98/917-3) (Fig. 4). However, despite TDr-98/917-3 producing 1 tuber, the tuber weighed more than the individuals with more than 1 tuber each. This still reaffirms the low propagation ratio of yam which several research has been devoted into finding a lasting solution to improve (Aighewi et al., 2015).
Following the protocol of Takrama (2000) in extracting the DNA of the individual plants in the three accessions, good quality DNAs were extracted (Plate 1). The genotypic profiling of the individual plants in the three accessions with 10 codominant SSR markers revealed a varied clustering arrangement not limited to accession groups. Six clusters were observed, with cluster 1 having 2 TDr-3010 and 1 TDr-893x903 individuals, cluster 2 and 5 had TDr-3010 (2) and TDr-893x903 (1) and TDr 98/917 (1) individuals, cluster 3 had one individual each of TDr-3010, TDr-893x903 and TDr 98/917. Cluster 4 had TDr 98/917 (3) only, while cluster 6 had only one individual of TDr 98/917 (Fig. 5a). Just like the cluster result, the Principal Component groupings presented a scattered arrangement of the individual plants of the three accessions (Fig. 5b).
Based on the phenotypic information, the individuals were grouped into 3 clusters, with cluster 1 having 4 individuals each from TDr-3010 and TDr/98–917, cluster 2 had 3 individuals each from TDr-3010 and TDr/98–917 and 1 from TDr-893x903 accession, while cluster 3 had 3 individuals from TDr-893x903 accession (Fig. 6a). Also, based on the Principal Component Analysis, the individual plants were grouped into 2, with all individuals from TDr-893x903 accession being grouped together, while the TDr 98/917 and TDr-3010 individuals were grouped together (Fig. 6b).
Yam is traditionally propagated using the tuber part (Balogun and Gueye, 2013). This method help maintains the genetic purity of the plant from one generation to another as the offspring originates from the somatic part, thus they are true to type and conventionally termed ‘seed yam’ (Aighewi et al., 2014). However, yam sometimes produces flowers and bears fruit, which can be harvested and used for breeding programs (Asiedu et al., 1998). Through this means, ‘yam seed’ is being produced. But the seeds are not true to type, which is not in the interest of commercial seed companies but the breeders that requires such in generating improved varieties for release. On the down side, there is non-synchronization of flowering in yam, thereby elongating yam breeding period (Asiedu et al., 1998). The yam seed originating from the flowering part developed through pollination and cross fertilization explains why progenies of same accession tends to differ in the genotypic and phenotypic characteristics as half of the genetic components of the parent lines are being contributed to form the offspring. Then the issue of contribution proportionality, dominant and if the system of inheritance obeys mendellian laws or a deviant of it coupled with the environmental conditions controls the genotypic constituent of the progeny. On the phenotypic characters exhibited, progenies of same accession tends to cluster more closely as the phenotype is a multiplicative result of genotype and environment. Thus, they exhibited epigenetic control, as though there are slight genetic changes in the offsprings as revealed by the genetic analysis using the codominant markers, they tend to exhibit similar phenotypic features.