Selection of superior genotypes of Indian jujube (Ziziphus mauritiana Lamk.) as revealed by fruit‐related traits

Abstract The nutritional and medicinal benefits of Ziziphus mauritiana Lamk. have led to its attention. Here, morphological and pomological diversity of this species was investigated. Most of the characters recorded showed considerable differences among the genotypes studied. The range of ripening data was from mid‐February to mid‐March. Fruit weight ranged between 15.68 and 33.62 g with an average of 24.17. Strong diversity was observed among the genotypes in terms of fruit skin ground color, ranging from light green to orange. There were significant correlations between some characters especially between the traits related to fruit size. Principal component analysis (PCA) classified the traits into 12 main components, justifying 75.07% of the total variance. The studied genotypes were grouped into two main clusters, indicating strong diversity among them. The present information might be used to choose the genotypes with the desired traits. Twenty‐one genotypes were promising because of high values of fruit weight, fruit taste, fruit skin color, and fruit quality, and thus, they can be recommended for direct cultivation and also to be used in breeding programs. The genotypes with superior traits can be further used for improvement through selection and hybridization to get desired traits.


| INTRODUC TI ON
Indian jujube (Ziziphus mauritiana Lamk., Rhamnaceae family) is rich in nutritional and medicinal properties. Tropical regions of South Asia, Australia, and Africa are its main distribution centers (Pasternak et al., 2009). In the arid and semi-arid regions, this plant is multipurpose and also can be used to prevent soil erosion (Gupta, 2018;Pareek, 2001). It has been confirmed that Indian jujube has high tolerance to salinity, drought, flooding, and withering (Grice, 1997). The medicinal and nutritional benefits of this plant have led to its attention. Vitamins are detected in its fruits. It is used as a sedative and anticancer. Also, it is suitable as wound healer and also against asthma (Ashraf et al., 2015;Hudina et al., 2008;Mishra et al., 2011;Nyanga et al., 2013). The antioxidant activity of its fruits (Gupta, 2018;Okala et al., 2014), seeds (Bhatia & Mishara, 2009), and leaf (Dahiru & Obidoa, 2007;Gupta, 2018) have been detected.
Self-incompatibility and cross-pollination have increased genetic variation of Indian jujube. There are superior genotypes in Z. mauritiana with high values for commercial characters that are cultivated in the orchard via asexual propagation methods (Devanshi et al., 2007).
The breeding programs of plants need suitable genetic variation.
Evaluation of genetic variability is essential for efficient application in breeding programs as well as for the implementation of conservation strategies. Lack of awareness of the genetic diversity and distribution of a plant species is one of the main obstacles to germplasm management. The study of genetic diversity is essential to identify distinct and superior genotypes, to explain the relationship between genotypes, and to manage and use germplasm properly (Awasthi et al., 2009;Hurtado et al., 2012).
The selection does not make diversity in germplasm because it creates small populations for breeders so that they can find ideal genotypes (Pommer, 2012). Choosing the suitable cultivar for successful cultivation with acceptable yield in specific areas is very important (Aulakhet al., 2000). The interaction between genetics and environment has an important function in expressing qualitative and also quantitative traits of a genotype. Morphological descriptions are still the first step in assessing the phenotypic diversity of plants helping breeders to identify genotypes with desired traits (Jannatabadi et al., 2014;Khadivi-Khub et al., 2014).
The Z. mauritiana is distributed in the southern parts of Iran, but little research has been done on this species. Therefore, phenotypic diversity of this important species was performed for the selection of superior genotypes for cultivation. The obtained information can be also useful in the protection and management of the genotypes.

| Plant material
Here, 119 genotypes of Z. mauritiana were chosen from different areas of Sistan-va-Baluchestan province in the south of Iran, and then, their morphological and pomological variation was evaluated.
The geographical characteristics of the sites studied are shown in Table 1. The selected genotypes are the most important cultivated trees in the study areas. The orchard management operations, including nutrition, irrigation, and pest and disease control, were performed regularly and uniformly for the genotypes.

| The recorded characteristics
Phenotypic variability of the genotypes was investigated based on 44 quantitative and qualitative characters related to tree, leaf, and fruit ( Table 2). The 50 mature leaves and 50 mature fruits were used to record the related characters. A digital caliper was used to measure the characters related to dimensions of leaf and fruit. Also, an electronic balance with 0.01 g precision was used to measure the characters related to weights of fruit. The qualitative characters were recorded according to rating and coding (Table 3).

| Data analysis
Analysis of variance (ANOVA) was performed using SAS software (SAS Institute, Cary, NC, & USA, 1990). Simple correlations between the traits were done using Pearson correlation coefficient with SPSS software (PSS Inc., Chicago, IL, USA;Norusis, 1998). Principal component analysis (PCA) was used to study the relationships among the genotypes with SPSS software. Hierarchical cluster analysis (HCA) was performed using Ward's method and Euclidean distance with PAST software (Hammer et al., 2001). Also, the scatter plot was created using the first and second principal components (PC1/PC2) with PAST software.

| Description of characteristics
Considerable diversity was observed among the studied genotypes, as revealed by the characteristics recorded. The tendency to form sucker exhibited the greatest CV (123.58%). Also, trunk color (76.36%), fruit skin over color (70.96%), leaf serration shape (55.76%), tree growth habit (51.57%), and fruit density (51.54%) showed high CVs. Besides, the CV was more than 20.00% in the majority of characters recorded (63.36% of characters) and thus revealed significant diversity within the germplasm studied (Table 2).
In contrast, six characters did not show differences, including leaf shape (lanceolate), leaf serration depth (low), leaf pubescence (present), shoot spine (present), fruit stone flesh (present), and surface of fruit stone (coarse), and thus, they can be considered as stable traits. Sharif et al. (2019) studied Z. mauritiana genotypes from Pakistan and reported that canopy density, color leaf lower surface, color of leaf upper surface, leaf shape, petiole length, fruit shape, fruit weight, and fruit stone shape showed high CVs.

| PCA
The PCA is used to find the most important traits in the data set.
The purpose of the PCA is to identify a number of key components to reduce the number of characters influencing the differentiation of genotypes (Iezzoni & Pritts, 1991). Also, the relationship between the traits emphasized by this method may be consistent with the genetic link between the trait control position and the multifunctional effect (Khadivi-Khub et al., 2014). The PCA classified the traits into 12 main components, justifying 75.07% of the total variance (

TA B L E 4 (Continued)
the genotypes (Figure 2). The genotypes were distributed on the plot and were divided into two groups with four subgroups.

| HCA
The genotypes studied were placed into two major clusters according to all the traits using HCA (Figure 3). The first cluster (I) included two subclusters. Subcluster I-A consisted of 27 genotypes, and subcluster I-B contained 27 genotypes. The remaining genotypes were classified into the second cluster (II), forming two subclusters.
Subcluster II-A consisted of 43 genotypes, and subcluster II-B contained 22 genotypes. Besides, population analysis showed that the studied populations were divided into three main groups (Figure 4). The diversity observed in the fruit size and quality-related characteristics between the studied genotypes can encourage the implementation of breeding programs. The results also showed that fruit weight among different genotypes has considerable diversity. The variation in fruit weight among the genotypes grown in the same geographical areas is due to differences in genetic basis and ecological conditions (Umbreen et al., 2018). The genotypes with high fruit weight can be selected for fresh fruit production and introduction to growers. The length and width of the fruit, which are important traits for breeders, also showed considerable diversity. The study of fruit size-related traits is of great importance for packaging and shipping judgments. Also, the color and taste of the fruits of different genotypes showed a great diversity, which can help breeders to choose genotypes according to the type of consumption ).

| CON CLUS ION
The current findings can be widely used to introduce cultivars in

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.

R E S E A RCH I N VO LV I N G H U M A N PA RTI CI PA NTS A N D/ O R A N I M A L S
None.

I N FO R M E D CO N S E NT
None.

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.