In the present study ISSR profile was used for diversity analysis and relationship among different A. hypogaea accessions. Several studies on populations indicate the percentage of the polymorphic locus as an important measure of genetic diversity [14]. A. hypogaea showed moderate genetic diversity as indicated by percent polymorphic loci (p = 51.8%). A study reported 54% of polymorphism among 13 A. hypogaea accessions using ISSR markers [15]. The observed highest Nei’s gene diversity (H) value (0.38 ± 0.174), and the highest Shannon’s indices (0.41 ± 0.194) shows presence of genetic diversity among the studied accessions. The Shannon index vary from 0 to 1, and lower genetic diversity is represented by values closer to zero [39].
In the present study, the PIC value varied from 0.29 (primer UBC881), less informative to 0.76 (primer UBC857), high informative with an average value of 0.49. PIC value of 0.70 and above is highly informative whiles a value of ~ 0.44 is moderately informative. PIC is a statistic that measures the usefulness of a genetic marker for linkage analysis [38].
The genetic differentiation of a species reflects the interactions of various evolutionary processes including long-term evolutionary history, such as shifts in distribution, habitat fragmentation and population isolation, mutation, genetic drift, mating system, gene flow and natural selection [42]. The coefficient of gene differentiation (Gst) for the entire accessions of A. hypogea was 0.29, suggesting a restricted genetic differentiation between accessions. The average value of differentiation might reflect the interactions of various factors including reduced geographic range in most of the accessions, inter and intra-regional climates, their breeding system and limited genetic drift or genetic isolation of the samples.
Based on the Gst value, the mean estimated number of gene flow (Nm) for the entire accessions was found to be 0.827 (Table 4). In flowering plant, the level of Nm is divided into three grades: high, Nm equal to or larger than 1.0; moderate, Nm ranging from 0.250 to 0.99; and low, Nm ranging from 0.00 to 0.249 [43]. Gene flow is generally considered as the main factor that could homogenize the genetic structure of populations in their distribution area. According to Wright (1931) [44], Nm¼ 1 is sufficient to overcome the effects of genetic drift. Also, species with low gene flow have higher genetic differentiation than species with high gene flow. However, our results indicated that virtually moderate gene flow occurred between the accessions of A. hypogaea.
Based on Jaccard’s similarity coefficient, highest genetic similarity observed among accessions suggests that the existence of genetic similarity among the accessions possibly due to gene flow. On the other hand, the least genetic similarity observed between some accessions is useful in broadening genetic base of A. hypogaea accessions in Ethiopia and these accessions should be considered as the primary/valuable sites in conservation and breeding program of the crop. Both PCoA and UPGMA cluster analysis shows the clustering of all 43 accessions into five clusters without clear geographical differentiation. This might be due to gene flow caused by the exchange of seeds by farmers in Ethiopia.
Knowledge on the genetic diversity of the selected individuals is of ultimate importance, since it contributes to the information on the species and allows the selection of genotypes to be included in future conservation programs. Thus, the most divergent genotypes can be selected to maintenance the level of genetic diversity of a species to keep its ability to adapt to novel environmental changes. The present finding also contributes valuable information on the genetic diversity of A. hypogaea accessions grown in Ethiopia.
Parameters such as MI and EMR have been used for assessing the informative potential of molecular markers in various genetic diversity studies [31, 34]. In the present study, the primers that generated high number of bands had higher MI and EMR values. MI and EMR were positively correlated with RP (r = 0.924 and r = 0.738, respectively, P < 0.01) and PIC. The resolving power (RP) is a parameter that specifies the discriminatory potential of the primers (the ability of a primer to generate optimally informative bands). Many studies have indicated RP index as an important feature of a good marker system [34, 35, 36, 37]. In the present study, the highest RP value 18.34 (UBC-857 ) suggesting the capacity of the primer used to distinguish among different accessions. RP was positively correlated with total amplified bands, number of polymorphic bands, MI and EMR at P < 0.01, suggesting the informativines of the ISSR primers used in the present study.
ISSR markers have demonstrated their efficiency in the study of genetic variability for several other species. Many studies have proved the effectiveness of this marker in articles on genetic diversity and characterization of accessions between and within populations, such as those with, Capparis spinosa L. [45], Pitcairnia flammea [46] Erythrina velutina [47] and Croton tetradenius [48].