1. Introduction
Peach (
Prunus persica) is a widely cultivated plant grown for both its blossoms and fruit around the world. Recently, peaches have become increasingly popular among consumers globally due to their attractive appearance, nutritional value, and distinctive flavor characteristics, such as sweetness and aroma [
1]. Peach fruits are rich in vitamins and trace elements [
2,
3]. Furthermore, they are abundant in phenolic compounds (e.g., flavan-3-ols, flavonols, and anthocyanins), which confer strong antioxidant properties beneficial to human health [
4]. Rossato et al. (2009) [
5] demonstrated that chlorogenic acid extracted from peaches exhibits excellent antioxidant activity and may enhance consumer health. Zhao et al. (2015) [
6] pointed out that peach varieties rich in hydroxycinnamate and flavan-3-ols exhibit relatively high antioxidant activity and could serve as valuable sources of natural antioxidants. Studies have also suggested that antioxidants in peaches may help reduce inflammation, protect the liver, and support the immune system [
7].
Molecular markers are genetic indicators based on variations in nucleotide sequences within the DNA of different individuals, directly reflecting genetic polymorphism at the molecular level. These markers are powerful tools for assessing genetic diversity and distinguishing individuals from various sources [
8]. For instance, a high-resolution genetic linkage map of peach has been developed using random amplified polymorphic DNA (RAPD) [
9], sequence-related amplified polymorphism (SRAP) [
10], simple sequence repeat (SSR) [
11,
12], and single nucleotide polymorphisms (SNP) [
13]. ISSR markers detect polymorphisms in inter-microsatellite DNA regions without requiring prior sequence information and have proven effective for studying genetic diversity, identifying varieties, constructing genetic maps, and localizing or cloning genes in fruit trees. Compared to other molecular markers, such as SSR or RAPD, ISSR markers are simple to use and capable of producing a high number of polymorphisms. Huang et al. (2012) [
14] demonstrated that RAPD and SSR markers were unable to distinguish between mandarin (
Citrus reticulata Blanco) varieties, whereas ISSR and SRAP markers successfully resolved their genetic relationships. Shen et al. (2020) [
15] analyzed 48 jujube cultivars from seven geographic regions in Northern China using ISSR markers, revealing correlations between genetic relationships and geographic origins. Similarly, ISSR markers demonstrated high genetic variation among Turkish apple cultivars [
16].
In peaches, ISSR markers have been utilized for cultivar identification. Sharma and Sharma (2018) [
9] analyzed 45 peach cultivars using ISSR markers, confirming their effectiveness in evaluating genetic diversity within peach germplasms. Tian et al. (2015) also used nine ISSR primers to assess the genetic diversity of 48 peach samples across three regions in China [
17]. Additionally, ISSR markers successfully amplified specific DNA bands in the ’Piqiu’ peach and its natural mutant, indicating slight genetic differences at the DNA level [
18]. Demeril et al. (2023) [
19] successfully evaluated the genetic diversity and population structure of 52 local peach genotypes and two commercial peach cultivars in Turkey using 32 ISSR markers.
In Vietnam, peaches are widely grown in northern region such as the Lao Cai, Son La, Lai Chau, and Lang Son provinces. Farmers grow peaches not only for fruit but also for its blossoms. Peach blossoms are a distinctive symbol of spring in Vietnam, especially in the northern provinces, where they enhance the beauty of the scenery but also carry profound cultural significance. During the Lunar New Year (Tet), households display peach blossoms as a wish for luck, prosperity, and happiness in the coming year.
However, peach varieties are primarily identified based on morphological differences and cultivation regions, which poses challenges for conservation and breeding selection. The application of DNA markers for genetic diversity evaluation in peach is still limited. In this study, we applied ISSR markers to evaluate the genetic diversity and relationships among peach varieties from northern mountainous provinces of Vietnam, including Lang Son, Cao Bang, Ha Giang, Tuyen Quang, and Son La. The goal is to assess genetic diversity to support the management and utilization of high-quality germplasm for peach breeding programs in Vietnam.
4. Discussion
Molecular markers such as RAPD, SSR, and ISSR have emerged as powerful tools for analyzing genetic diversity and relationships among peach varieties. These methods provide insights into genetic polymorphism and are valuable for breeding, germplasm conservation, and crop improvement. The Polymorphism Information Content (PIC) value is crucial for selecting molecular markers.
Ramzan et al. (2020) [
22] used 10 ISSR markers to assess genetic diversity among Tamarix ecotypes and revealed that ISSR markers produced 131 bands, of which 116 were polymorphism (88.5%), with a mean PIC value of 0.34. In another study, Hu et al. (2006) [
23] analyzed the genetic relationships among ornamental peach varieties using 10 ISSR markers. They amplified a total of 132 alleles, with 62% of the bands being polymorphic. Their findings indicated that
Prunus davidiana (Carr.) was clearly an outgroup of
P. persica, and its hybrids clustered together, indicating that
P. davidiana is related to ornamental peach varieties, which are genetically distinct from
P. persica cultivars.
Based on the results presented in
Table 1, the primers used in this study showed PIC values ranging from 0.18 to 0.3, with an average PIC value of 0.27. Among these, the ISSR4 and ISSR11 primers had the highest PIC value (0.3), while the ISSR3 primer had the lowest PIC value of 0.18. The PIC values for the ISSR1, ISSR8, and ISSR14 primers were 0.26, 0.26, and 0.27, respectively. The alleles size ranged from 200 to 2000 bp.
These findings are similar to those reported by Sharma and Sharma (2018) [
9], who evaluated 45 peach genotypes using 46 ISSR markers, obtaining PIC values ranging from 0.12 to 0.49 and allele sizes between 100 and 900 bp. Similarly, Drogoudi et al. (2023) [
24] used eight ISSR markers to evaluate 43 peach genetic resources, reporting high PIC values ranging from 0.349 to 0.404 and allele sizes between 230 and 2500 bp. Li et al. (2023) [
10] analyzed genetic diversity and relationships among 39 late-peach varieties using ISSR markers and found substantial diversity among accessions, with similarity coefficients ranging from 0.65 to 0.89. Although they were divided into two groups, most of them (38 accessions) clustered together.
Based on pooled analysis of six ISSR markers, the similarity coefficients among the 59 accessions ranged from 0.46 to 1.0, and they were grouped into two main clusters (
Figure 3). Cluster I consists of 32 accessions, with 30 collected from Bac Kan province, including 15 DTPA accessions (DTPA1-15) from Ban Mach village, Na Phac commune, Ngan Son district and 13 DSDL accessions (DSDL1-13) from Ban Vang village, Dia Linh commune. Two additional accessions (DDKN and DDCT) were collected from Khang Ninh and Cao Thuong communes, Ba Be district. They were divided into sub-groups Ia and Ib, respectively. Interestingly, two accessions collected from Bac Ha district, Lao Cai province (DVBH) and Tam Duong district, Lai Chau province (DDCT) showed a close relationship with sub-group Ib (
Figure 3). Cluster II includes 24 accessions collected from 10 different provinces (Lao Cai, Ha Giang, Cao Bang, Bac Kan, Dien Bien, Yen Ba, Lang Son, Nghe An, Son La, and Lai Chau) and was divided into two subgroups: IIa (22 accessions) and IIb (2 accessions). Within subgroup IIa, at a similarity coefficient of 0.758, the accessions were further divided into two second-level subgroups (IIa1 and IIa2). Additionally, three accessions (DXTQ, DPD2, and DRTU) did not group with the others and exhibited significant genetic distances. Overall, these results show that although peach varieties were collected from different provinces, most of the accessions exhibit a moderate to low genetic variation between regions, which is consistent with previous reports [
24,
25,
26].
Genetic differences in peach have been investigated to be not significantly influenced by geographical distance [
17,
27,
28]. Li et al. (2014) [
27] analyzed 80 peach cultivars collected from five different regions in China using AFLP markers, with the result that most of the genetic variations occur within the population. There is no close relationship between geographic distance and genetic distance. Similarly, Tian et al. (2015) [
17] reported that 48 peach accessions collected from three different regions showed no correlation between geographical distance and genetic diversity. There was only a 4% genetic difference among 85 peach cultivars collected from Russia, Europe, and South America [
28]. In this study, the correlation analysis of genetic relationships and geographical distance among 59 peach cultivars from 19 different locations also showed no correlation.
In Vietnam, the trading and exchange of peach blossoms are highly active before the “Tết” holiday (Lunar New Year). Peach traders often transport and sell peach trees across various provinces in the northern mountainous region. These trees are usually planted in home gardens after “Tết”. This could explain why, despite geographical distances, many peach accessions have similar genetic distances. Most of the peach varieties in this study have attractive blossoms, and farmers often prune their branches or entire plants for sale. Trading and exchange activities among farmers may lead to genetic drift, resulting in peach varieties being renamed based on their localities. For example, the DDYD accession, grown in Yen Duong Commune, Ba Be District, Bac Kan Province, showed a close genetic relationship (coefficient = 0.9) with the DNN2 accession, collected in Ta Chai commune, Bac Ha district, and Lao Cai province.
Taken together, in peach, genetic variations occur in groups and are not influenced by geographical distance. Therefore, in the conservation of the valuable peach germplasm, ex situ conservation can be applied.
