J. AMER.SOC.HORT.SCI. 146(1):68–76. 2021. https://doi.org/10.21273/JASHS04956-20 Karyotypic Characteristics and Genetic Relationships of Apricot Accessions from Different Ecological Groups Wenwen Li, Liqiang Liu, Weiquan Zhou, Yanan Wang, and Xiang Ding College of Horticulture and Forestry, Xinjiang Agricultural University, Urumqi, Xinjiang 830052, China Guoquan Fan and Shikui Zhang Luntai National Fruit Germplasm Resources Garden of Xinjiang Academy of Agricultural Sciences, Luntai, Xinjiang 841600, China Kang Liao College of Horticulture and Forestry, Xinjiang Agricultural University, Urumqi, Xinjiang 830052, China ADDITIONAL INDEX WORDS. chromosome number, diversity, karyotype analysis, P. armeniaca ABSTRACT. The present study aims to reveal the karyotypic characteristics and genetic relationships of apricot (Prunus armeniaca L.) accessions from different ecological groups. Fourteen, 9, and 30 accessions from the Central Asian ecological group, North China ecological group, and Dzhungar-Ili ecological group, respectively, were analyzed according to the conventional pressing plate method. The results showed that all the apricot accessions from the different ecological groups were diploid (2n =2x = 16). The total haploid length of the chromosome set of the selected accessions ranged from 8.11 to 12.75 mm, which was a small chromosome, and no satellite chromosomes were detected. All accessions had different numbers of median-centromere chromosomes or sub-median-centromere chromosomes. The karyotypes of the selected accessions were classified as 1A or 2A. Principal component analysis revealed that the long-arm/short-arm ratio (0.968) and the karyotype symmetry index (L0.979) were the most valuable parameters, and cluster analysis revealed that the accessions from the Central Asian ecological group and Dzhungar-Ili ecological group clustered together. In terms of karyotypic characteristics, the accessions from the Dzhungar-Ili ecological group and Central Asian ecological group were closely related. Fruits are plant-derived products that can be consumed in including wild species, and cultivated species, were divided their raw form without undergoing processing or conversion. into six ecological groups by Chinese scholars (Zhang and Several fruit groups, including temperate, tropical, and sub- Zhang, 2003), namely, Central Asian ecological group (CAG), tropical, are adding value to the earth’s diversity and are Dzhungar-Ili ecological group (DZG), North China ecological fundamental to all life. They include high contents of non- group (NCG), European ecological group (EG), Northeast nutritive, nutritive, and bioactive compounds (Gecer et al., Asian ecological group, and East China ecological group. The 2020; Senica et al., 2019; Serc¸e et al., 2010). Apricot (P. apricot accessions in these groups displayed extensive mor- armeniaca), which belongs to the Rosaceae family, is culti- phological and physiological differences as well as extensive vated worldwide (Jiang et al., 2019). According to different adaptability to different ecological zones (Zhang and Liu, taxonomic systems, there are six Prunus L. species that are 2018). recognized by most scholars: P. armeniaca, Prunus sibirica L., The Kashgar, Hotan, and Kuqa oasis areas around the Tarim Prunus mandshurica (Maxim.) Skv., Prunus holosericea Basin in the southern part of the Xinjiang Uygur Autonomous (Batal.) Kost., Prunus mume Sieb. et Zucc., and Prunus Region, China, are the main areas of apricot production and brigantina Vill. (Bortiri et al., 2001). Nearly all cultivated contain the greatest abundance of apricot cultivars. The wild apricot accessions originated from P. armeniaca (Zheben- apricot forest in Ili, Xinjiang, China, is a relic of broad-leaved tyayeva et al., 2003). On the basis of their geographical forests from the late Tertiary and played a decisive role in the distribution characteristics, apricot plants across the world, domestication and cultivation of apricot trees worldwide (Zhebentyayeva et al., 2003). This forest is an important part of the deciduous broad-leaved forest below the montane Received for publication 11 June 2020. Accepted for publication 29 Oct. 2020. coniferous forest and above the montane grasslands in Xinjiang Published online 8 December 2020. This work was supported by the National Key Research and Development (Zhang and Zhang, 2003). Only one mountain separates the Program (grant no. 2016YFC0501504), the Xinjiang Uygur Autonomous southern Xinjiang and Ili areas in the northern Tianshan Region Horticulture Key Discipline Fund (grant no. 2016-10758-3), and the Mountains, and there are several corridors between the northern Xinjiang Agricultural University Crop science postdoctoral research station. and southern Tianshan Mountains. Geographically, cultivated We thank American Journal Experts for editorial assistance with the English. K.L. is the corresponding author. E-mail: [email protected]. apricot trees in the southern Tianshan Mountains of Xinjiang This is an open access article distributed under the CC BY-NC-ND license (CAG) most likely evolved from the spread of wild apricot (https://creativecommons.org/licenses/by-nc-nd/4.0/). trees in the Ili Valley (DZG). Information on differences in 68 J. AMER.SOC.HORT.SCI. 146(1):68–76. 2021. chromosome number and karyotypic characteristics between wild (wild accessions), were collected. The seeds of 23 of the and cultivated species can be used as an important tool in fruit tree cultivated accessions were provided by the Luntai National heredity and breeding (Kazem et al., 2010). Furthermore, wild Fruit Germplasm Resources Garden of the Xinjiang Academy species can provide an abundance of germplasm resources for of Agricultural Sciences. The seeds of 30 wild accessions were improved breeding selections or lines (Kazem et al., 2010). collected from the natural distribution areas of wild fruit forests Variations in chromosome number and karyotypic character- within Xinyuan County, Yining County, and Huocheng County istics are the main mechanisms governing species diversification (Xinjiang, China) (Fig. 1, Supplemental Table 1). (Martin et al., 2015). The chromosome number is an important CHROMOSOME COUNT. The chromosomes of metaphase cells feature in plant cell taxonomy and can provide information about were counted according to the conventional pressing plate polyploidy and other important genomic changes (Jang et al., method. Chromosome preparation was improved by adopting 2013). In addition to the chromosome number, the chromosome the methods of Sun et al. (2015) and Chen et al. (2013). The morphology is often used in plant classification (Martin et al., endocarp was removed from each collected seed, after which –1 2015). Karyotypic analysis can be used to understand relation- the seed was soaked in 150 mgÁL gibberellic acid (GA3) for 24 ships among species, processes leading to evolutionary diversi- h followed by distilled water for 12 h. Root tips were cultured fication, and the direction of evolution. Chromosomal changes on moist filter paper in a petri dish, after which they were cut to play an important role in plant evolution, diversification, and 1.0 to 1.5 cm in preparation for treatments. The root tips were speciation (Jang et al., 2013). These data can also help to subsequently cut to 0.5 cm between 0900 and 1000 HR.At4°C, elucidate the origin, morphology and phylogenetic relationships the root samples were pretreated in 0.29 gÁL–1 8-hydroxyquino- among plant genotypes (Alberto et al., 2003). line solution for 6 h and then fixed in fixation solution (3 methyl A number of cytological studies during the past few decades alcohol:1 acetic acid) for 24 h. The fixed root tips were rinsed have provided essential characteristics for phylogenetic and twice with 95% ethanol and then stored in 70% ethanol at 4 °C evolutionary analyses (Stace, 2000). However, the number of for subsequent use. The root tips were acidified in an 83 mLÁL–1 chromosomes is known for only 25% of all angiosperms hydrochloric acid solution (36% to 38%) at 60 °C for 15 min, (Baltisberger and Widmer, 2009). According to the Chromo- after which they were immersed in distilled water (hypotonic some Counts Database (Rice et al., 2015), the chromosome conditions) at room temperature for 30 min. Last, the root trips number of P. armeniaca is 16. Since the 20th century, the were placed on slides and stained with carbol fuchsin (Sigma- chromosomal characteristics of apricots have aroused the Aldrich, St Louis, MO) for 45 min. The slides were observed interest of scholars (Lin et al., 1999; Lv, 1986; Wang et al., under ·100 objectives of the microscope (Eclipse 80i; Nikon, 1992; Wei and Tang, 1996). Early studies focused on the total Tokyo, Japan) and then imaged, and the chromosomes were number of chromosomes rather than the individual morphology counted with NIS-Elements F 3.0 software (NIS-Elements F or genetic significance of species revealed by their karyotype 3.0, Nikon). parameters. Lv (1986) used the conventional method to deter- CALCULATION OF KARYOTYPE PARAMETERS. A total of 15 mine that the chromosome number of P. armeniaca and P. independent karyotype parameters were determined according sibirica, both of which have small chromosomes, was 16 to their own formula. These karyotype parameters included the chromosomes. By using the conventional method, Wang following: Stebbins’ karyotype [SK (Stebbins, 1971)], mean et al. (1992) determined the karyotype formula for P. sibirica: long-arm/short-arm ratio [MAR (Zhang et al.,