Identification of the promising oleaster (Elaeagnus angustifolia L.) genotypes based on fruit quality‐related characters

Abstract The fruits of oleaster (Elaeagnus angustifolia L.) are rich in nutritional value and contain protein, sugar, vitamins, and minerals. The present investigation was performed to evaluate the morphological variability of the naturally grown accessions of this species. There was considerable variation among the accessions based on all the traits measured. The range of fruit weight was from 0.32 to 3.04 g, with an average of 1.48. Fruit yield was significantly and positively correlated with tree growth vigor, canopy density, branching, branch density, and leaf density. Principal component analysis (PCA) indicated nine components of data accounted for 74.93% of the total variance. Ward cluster analysis using Euclidean distance classified the accessions into two main clusters and showed significant differences among the accessions studied. Among the area studied, 14 accessions showed the highest value of fruit quality‐related characters, which are suitable for fresh consumption and health benefits. The results provided important information useful for selecting the preferred accessions for commercial cultivation and breeding programs.


| INTRODUC TI ON
Oleaster (Elaeagnus angustifolia L.) belongs to the family Elaeagnaceae and is a deciduous tree or shrub resembling an olive tree with small and reddish brown fruits (Fonia et al., 2009;Sahan et al., 2013). This plant's life is long and reaches 80-200 years, its growth is rapid that its height reaches 10 meters and 30 cm in diameter, and its fruiting begins after 5-6 years (Kiseleva & Chindyaeva, 2011). This plant has high tolerance to a wide range of adverse environmental conditions such as severe drought, flooding, and rocky and saline soils (Asadiar et al., 2013). Different parts of this tree have many medicinal uses and are used in the perfume industry. Also, its wood is used in woodworking and musical instruments (Kiseleva & Chindyaeva, 2011).
The nutritional value of E. angustifolia fruits is considerable, owing to significant amounts of protein, sugar, vitamins, and minerals (Fonia et al., 2009;Taheri et al., 2010). Its fruits are eaten fresh or dried and are rich in vitamin C, thiamin B1, and minerals such as calcium, manganese, iron, potassium, and magnesium. It contains tocopherol and carotene (Boudraa et al., 2010).
Genetic variation generated and maintained by evolution is an inherited diversity among populations (Demol et al., 2001) and is also an important intrinsic trait that helps breeders develop breeding programs. Phenotypic description of plants has been introduced as an efficient method for identifying elite individuals. This method is an important tool for selecting varieties or lines based on morphological and agronomic traits (Bajracharya et al., 2006;Ndour, 1998).
A proper characterization of genetic resources is necessary to develop breeding strategies. Native genetic resources are welladapted and also are interesting gene pools for breeding programs.
The first step in the description and classification of the plants is morphological characterizations. Statistical methods such as principal component and cluster analyses are useful tools for describing and screening accessions in a germplasm collection (Peeters & Martinelli, 1989).
The study of food-drug fruit species can help protect them as well as their use in breeding programs and health-related industries.
The present study was performed to evaluate the phenotypic diversity of naturally grown accessions of E. angustifolia to select superior accessions in terms of fruit quality.

| Plant material
The present study was performed to evaluate the phenotypic diversity of 84 naturally grown accessions of E. angustifolia to select

| The characters evaluated
In total, 28 morphological characters (Table 1) were used for phenotypic diversity of the accessions studied. Fifty replicates for leaf and fruit were used for measurements, and the mean values were used for analysis. Leaf length, leaf width, petiole length, petiole thickness, thorn length on annual shoot, thorn base thickness on annual shoot, fruit length, fruit width, fruit stalk length, fruit stalk diameter, fruit flesh thickness, stone length, and stone width were measured by a digital caliper. Fruit fresh weight, fruit dry weight, and stone weight were measured by using an electronic balance with 0.01 g precision.
In addition, the rest traits (

| Statistical analysis
The meaningful differences between the accessions in terms of the traits measured were determined using one-way analysis of variance (ANOVA) by SAS software (SAS Institute, 1990). The parameters, including minimum, maximum, mean, standard deviation, and coefficient of variation (CV), were calculated. The Pearson correlation coefficient was used to determine the correlation between traits with SPSS ® software version 16 (SPSS Inc. Norusis, 1998). The relationship between the accessions was analyzed with principal component analysis (PCA) using SPSS software. Cluster analysis was performed using the Euclidean distance coefficient and Ward method with PAST software (Hammer et al., 2001). Distance coefficients were standardized using Z scale. In addition, the first and second principal components (PC1 and PC2) were used to generate the scatterplot with PAST software. Brown fruit color was predominant (46) and followed by yellow (30). Fruit taste was astringent in 11, slightly sweet in 29, sweet in 27, and very sweet in 17 accessions. Khadivi (2018) reported that fruits in the majority of E. angustifolia genotypes had a sweet taste.

| RE SULTS AND D ISCUSS I ON
Seed length ranged from 12.11 to 29.12 mm, seed width varied from 4.57 to 8.77 mm, and the range of seed weight was 0.17-0.75 g. The fruit's pictures of the studied accessions of E. angustifolia are shown in Figure 1.
The PCA method divided the traits into nine independent components, each of which had an eigenvalue higher than 1, justifying 74.93% of the total variance ( Bi-plot analysis performed using the traits placed into PC1 and PC2 showed the relationships among the accessions, and the individuals within each of these PCs were more similar and grouped with each other. According to the duplicate analysis, the accessions were located on the four sides of the plot (Figure 2). In the bi-plot, the accessions are represented in a two-dimensional form and are shown based on the traits affecting PC1 and PC2.
Cluster analysis is one of the methods in which several variables are used, and the purpose of this method is to classify individuals according to their characteristics. In the cluster analysis, the individuals within a class are highly similar to each other, with the highest nonuniformity and differences among clusters (Hair et al., 2009). In the cluster analysis based on Ward's method, the accessions were F I G U R E 4 Bi-plot for the studied areas of E. angustifolia based on morphological characters divided into two main groups according to morphological traits ( Figure 3). The first group (I) included two subgroups; subgroup I-A consisted of 19 accessions, and sub-group I-B contained 27 accessions. The rest accessions were classified as group II so that four accessions formed subgroup II-A, and subgroup II-B included 34 accessions.
In addition, the population analysis grouped the most similar areas within a group (Figure 4). The first cluster included the Senejan area, the second group consisted of Dehmahdi, and the third group included the Astaneh and Dehsad areas. There were great phenotypic variations among the accessions in terms of fruit-related characters. The chance of genetic conservation, genotype selection, and improvement is significantly increased by enhancing knowledge on genotypic diversity (Wani et al., 2014). The variation observed in the same population can be due to the genetic and environmental effects (Karadeniz, 2002).

| CON CLUS ION
Significant differences were observed among the accessions of E. angustifolia based on the characters. Among the area studied, 14 accessions belonging to the Dehsad area, including Dehsad-9, Dehsad-10, and Dehsad-21, showed the highest value of fruit quality-related characters, which are suitable for fresh consumption and health benefits.
The results provided important information that is useful for selecting the preferred accessions for commercial cultivation and breeding programs.

ACK N OWLED G M ENT
None.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.