Caryologia. International Journal of Cytology, Cytosystematics and Cytogenetics 75(1): 123-130, 2022 Firenze University Press www.fupress.com/caryologia ISSN 0008-7114 (print) | ISSN 2165-5391 (online) | DOI: 10.36253/caryologia-1387 Caryologia International Journal of Cytology, Cytosystematics and Cytogenetics Citation: Yuming Qian, Kailin Zhu, Chenqian Tang, Zhixin Qiu, Xin Chen (2022) Chromosome counts and karyo- type analysis of nine taxa in Sor- bus subgenera Aria and Micromeles (Rosaceae) from China. Caryologia 75(1): 123-130. doi: 10.36253/caryolo- gia-1387 Received: September 2, 2021 Accepted: March 20, 2022 Published: July 6, 2022 Copyright: © 2022 Yuming Qian, Kailin Zhu, Chenqian Tang, Zhixin Qiu, Xin Chen. This is an open access, peer- reviewed article published by Firenze University Press (http://www.fupress. com/caryologia) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All rel- evant data are within the paper and its Supporting Information files. Competing Interests: The Author(s) declare(s) no conflict of interest. ORCID YMQ: 0000-0002-7393-5099 KLZ: 0000-0003-0020-7207 XC: 0000-0003-2315-083X Chromosome counts and karyotype analysis of nine taxa in Sorbus subgenera Aria and Micromeles (Rosaceae) from China Yuming Qian, Kailin Zhu, Chenqian Tang, Zhixin Qiu, Xin Chen* Co-Innovation Center for Sustainable Forestry in Southern China, College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037,China *Corresponding author. E-mail: chenxinzhou@hotmail.com Yuming Qian and Kailin Zhu contribute equally to the article Abstract. Chromosome numbers of nine taxa in Sorbus subgenera Aria (Pers.) Host and Micromeles Decne. were determined. All are diploid with 2n = 2x = 34. Eight out of them: S. alnifolia (Siebold and Zucc.) K. Koch var. angulata S.B. Liang Rehd., S. alni- folia (Siebold and Zucc.) K. Koch var. lobulata (C.K. Schneid.) Rehd., S. dunnii Rehd., S. folgneri (C.K. Schneid.) Rehd., S. hemsleyi (C.K. Schneid.) Rehd., S. lushanensis X. Chen & J. Qiu, S. ochracea (Hand.-Mazz.) J.E. Vidal and S. yuana Spongberg, which are endemic to China, were reported for the first time. One remaining Asian native S. alnifolia var. alnifolia (Siebold and Zucc.) K. Koch, 2n = 34 was confirmed here. The chromosomes size and the total haploid chromosome length varied from 0.91 µm to 3.51 µm and 23.43 μm to 50.04 μm respectively. A predominance of metacentric chro- mosomes were perceived. Satellites were observed only in taxa of subgenera Microme- les. Nine taxa were classified as 1A, 2A and 2B according to the Stebbins classification. S. yuana in subgenus Aria presents the most symmetrical karyotype according to all the 11 quantitative indices analyzed, while S. dunnii and S. ochracea in Micromeles pre- sent the most asymmetrical karyotypes according to different indices. Keywords: chromosome number, karyotype asymmetry, Sorbus, subgenera Aria and Micromeles, China. INTRODUCTION The genus Sorbus L. (Rosaceae) comprises about from 67 (Lu and Spong- berg 2003) to at least 111 species in China (Phipps et al.1990). Chinese native species were traditionally assigned to three subgenera (three sections in the same names by Yü and Kuan (1963)): Aria (Pers.) Host and Micromeles Dec- ne. with simple leaved species, Sorbus with pinnately leaved species (Phipps et al. 1990). Polyploidy together with hybridization and apomixis is an important evolutionary force in shaping plant diversification in Sorbus (Robertson et al. 2010; Ludwig et al. 2013; Lepší et al. 2019). The number of species recognized in the genus varied between authors mainly depending on the way that the 124 Yuming Qian et al. numerous polyploidy apomicts were treated (Aldasoro et al. 2004; McAllister 2005; Sennikov and Kurtto 2017). Knowledge of chromosome numbers is high- ly important in Sorbus in understanding the species delimitation and relationship. Modern taxonomic stud- ies (McAllister 2005; Sennikov and Kurtto 2017) and descriptions of new species (Rich et al. 2014; Lepší et al. 2015; Somlyay et al. 2017) are accompanied to count of chromosome numbers or DNA ploidy levels based on flow cytometry. Polyploidy was reported only in subgenus Sorbus from China, which account for more than half of the sub- genus’ species richness and are distributed mainly in the mountains of southwest area, especially the Qinghai-Tibet Plateau (McAllister 2005; Li et al. 2021). For subgenus Aria, which is disjunctly distributed across Europe and Asia, with polyploidy species reported from only Europe (Sennikov and Kurtto 2017). For the Asian native subge- nus Micromeles, the only chromosome number available is S. alnifolia (2n = 2x = 34; Sax 1931; Baranec and Murín 2003). Though Aldasoro et al. (2004) suggested that the great variability in leaf outline of S. alnifolia might reflect the presence of agamospermous individuals in popula- tions, no evidence is available up to now. Agamospermy as a form of asexual reproduction is prevalent in Sorbus (Robertson et al. 2010; Hajrudinović et al. 2015) and other genera in Maloideae such as Amelanchier Medik. (Burgess et al. 2014), Cotoneaster Medik. (Rothleutner et al. 2016) and Crataegus L. (Talent and Dickinson, 2007) etc. The aim of this study is to investigate the chromo- some number, karyotype, idiogram and other detailed measurements of eight Chinese endemic taxa from Sub- genus Aria and Micromeles, together with an Asian dis- tributed species S. alnifolia, to find out whether there are polyploid and to analyze the species relationship. MATERIALS AND METHODS Plant materials Nine taxa, including two species in Sorbus subge- nus Aria: S. hemsleyi (C.K. Schneid.) Rehd. and S. yuana Spongberg, and seven taxa in subgenus Micromeles: S. alnifolia (Siebold and Zucc.) K. Koch var. alnifolia , S. alnifolia (Siebold and Zucc.) K. Koch var. angulata S.B. Liang, S. alnifolia (Siebold and Zucc.) K. Koch var. lob- ulata Rehd., S. dunnii Rehd., S. folgneri (C.K. Schneid.) Rehd., S. lushanensis X. Chen and J. Qiu, S. ochracea (Hand.-Mazz.) J.E. Vidal, were investigated. One species, S. ochracea, was collected from the Kunming Botani- cal Garden, and the remaining eight taxa were collected from wild populations between 2012 and 2016. Voucher specimens are deposited at the herbarium of Nanjing Forestry University (NF; Table 1). Chromosome counts Root tips were immersed in a mixed solution of 0.05% aqueous colchicine and 0.002 mol/L 8-hydroxy quinolone (1:1) at 0–4 °C for 2 h, and then fixed in Car- noy’s fixative (3:1 alcohol:glacial acid, v/v) for at least 24 Table 1. Localities and voucher specimens of Sorbus taxa examined in the present study. Taxa Locality Collector/Voucher specimen S. hemsleyi Wawushan Scenic Spot, Sichuan province, E102°57’06.82”, N29°39’54.35”, 2230 m, 25 September 2016 Xin Chen & Zhongren Xiong/0745 S. yuana Shennongjia Forestry District, Hubei province, E110°19’17.76”, N31°34’21.30”, 2173 m, 20 October 2016 Yun Chen & Yang Zhao/0817 S. alnifolia var. alnifolia Changbai Mountains, Jilin province, E127°49’24.85”, N42°02’04.85”, 867m Xin Chen & Dan Chen/2-1 S. alnifolia var. angulata Lushan Mountain, Shandong province, E118°03’09.00”, N36°17’45.31”, 1047 m, 9 October 2015 Xin Chen & Jing Qiu/0140 S. alnifolia var. lobulata Laoshan Mountain, Shandong province, E120°37’26.58”, N36°10’40.04”, 942 m, 28 October 2014 Xin Chen & Wan Du/0042 S. dunnii Huangshan Mountain, Anhui province, E117°26’18.07”, N29°11’36.31”, 1603 m, September 2013 Xin Chen & Dan Chen/4-7 S. folgneri Badong, Hubei province, E110°17’19.75” N30°41 ’36.86”, 1543 m, 17 October 2016 Yun Chen & Yang Zhao/0791 S. lushanensis Lushan Mountain, Jiangxi province, E116°00’46.29”, N29°32’58.59”, 1310 m, 2 October 2015 Xin Chen, Weiqi Liu & Mingwei Geng/0157 S. ochracea Kunming Botanical Garden, Yunnan province, E102°44’17.54”, N25°8 ’23.65”,1936 m, 5 August 2020 Qin Wang/0256-2 125Chromosome counts and karyotype analysis of nine taxa in Sorbus subgenera Aria and Micromeles (Rosaceae) h at room temperature. The root tips were hydro- lyzed in 1 mol/L HCl at 60 °C for 10 min, then were washed with distilled water for 2-3 min. The fixed roots were stained with Carbol fuchsin for 3-4 h and were squashed on glass slides for observation. No less than five cells per individual and three to five plants per taxon were examined. Photos were taken under a Nikon Eclipse Ci-S microscope. Karyotype analysis For the numerical characterization of the karyo- types, the following parameters were measured and calculated using KaryoType software (Altinordu et al. 2016): short arm length (S) and long arm length (L); mean length of the chromosome (CL); total haploid length of the chromosome set (THL); longest chro- mosome/shortest chromosome (Lt/St); ratio of mean long to short arm length (MAR); centromeric index (CI); coefficient of variation of the centromeric index (CVCI) and coefficient of variation of chromosome length (CVCL); mean centromeric asymmetry (MCA); the karyotype asymmetry index (AsK%); the total form percent (TF%); the index of karyotype symme- try (Syi%); the intra chromosomal asymmetry index (A1); the interchromosomal asymmetry index (A2); the degree of karyotype asymmetry (A); the disper- sion index (DI) and the asymmetry index (AI). Karyotype formula was determined by chro- mosome morphology based on centromere position according to Levan classification: median point (M, AR = 1.00), median region (m, AR = 1.01–1.70), sub- median (sm, AR = 1.71–3.00), subterminal (st, AR = 3.01–7.00) and terminal region (t, AR > 7.00). Satellite chromosomes were abbreviated as ‘sat’ (Levan et al. 1964). Idiograms were drawn using KaryoType based on length of chromosome size. Statistical analysis was carried out by using SPSS 26.0. RESULTS All nine investigated Sorbus taxa are diploids with 2n = 2x = 34. New counts were reported for eight Chinese endemic taxa, S. alnifolia var. angu- lata, S. alnifolia var. lobulata, S. dunnii, S. folgneri, S. hemsleyi, S. lushanensis, S. ochracea and S. yuana. For the remaining S. alnifolia var. alnifolia, the previously reported chromosome numbers was confirmed here. Karyotype characters of the nine taxa were reported for the first time (Table 2; Figure 1, 2). The Ta bl e 2. K ar yo ty pe fe at ur es o f t he n in e st ud ie d So rb us ta xa . Su bg en us Sp ec ie s 2n K ar yo ty pe fo rm ul a V C L (µ m ) T H L (µ m ) Lt /S t M A R St eb bi ns ’s ty pe C V C I C V C L M C A A sK % T F% Sy i% A 1 A 2 A D I A I A ri a S. h em sle yi 34 29 m +5 sm 0. 93 -1 .8 3 23 .4 3 1. 97 1. 33 2A 11 .5 1 18 .5 6 12 .9 2 56 .7 43 .3 76 .3 5 0. 22 0. 19 0. 13 7. 51 2. 14 S. y ua na 34 32 m +2 sm 1. 15 -1 .7 8 23 .4 4 1. 55 1. 27 1A 8. 36 11 .2 9 11 .0 6 55 .5 9 44 .4 1 79 .9 0. 19 0. 11 0. 11 5. 08 0. 97 M ic ro m el es S. a ln ifo lia v ar . a ln ifo lia 3 4 32 m (2 sa t) +2 sm 1. 48 -2 .4 9 32 .9 1 1. 68 1. 34 1A 9. 31 14 .2 13 .8 57 .0 2 42 .9 8 75 .3 8 0. 23 0. 14 0. 14 5. 73 1. 32 S. a ln ifo lia v ar . a ng ul at a 34 26 m +8 sm (2 sa t) 1. 04 -1 .8 6 24 .0 2 1. 78 1. 49 2A 13 .8 2 14 .7 9 18 .1 3 59 .4 1 40 .5 9 68 .3 2 0. 29 0. 15 0. 18 6. 45 2. 04 S. a ln ifo lia v ar . l ob ul at a 34 32 m (2 sa t) +2 sm 1. 27 -2 .5 6 31 .4 1 2. 01 1. 46 2B 9. 92 17 .7 2 17 .6 6 58 .8 41 .2 70 .0 6 0. 29 0. 18 0. 18 7. 14 1. 76 S. d un ni i 34 24 m (2 sa t) +1 0s m 2. 14 -3 .5 1 50 .0 4 1. 64 1. 51 2A 14 .5 7 14 .5 8 18 .4 9 59 .5 3 40 .4 7 67 .9 7 0. 30 0. 15 0. 18 5. 75 2. 12 S. fo lg ne ri 34 30 m (2 sa t) +4 sm 0. 91 -1 .9 6 24 .4 5 2. 15 1. 36 2B 9. 71 15 .6 8 14 .1 0 56 .9 9 43 .0 1 75 .4 7 0. 24 0. 16 0. 14 6. 95 1. 52 S. lu sh an en si s 34 30 m (2 sa t) +4 sm 1. 27 -2 .2 6 29 .2 1. 78 1. 39 2A 12 .0 5 16 .4 5 14 .9 4 57 .9 3 42 .0 7 72 .6 1 0. 25 0. 16 0. 15 6. 72 1. 98 S. o ch ra ce a 34 28 m (2 sa t) +6 sm 1. 26 -2 .5 29 .2 2 1. 98 1. 36 2A 11 .4 6 19 .9 2 13 .7 1 57 .1 1 42 .8 9 75 .1 1 0. 23 0. 20 0. 14 9. 38 2. 28 126 Yuming Qian et al. size of the chromosomes varied from 0.91 μm (0.91–1.96 μm) in S. folgneri to 3.51 μm (2.14–3.51 μm) in S. dunnii. The total haploid chromosome length (THL) changed from 23.43 μm in S. hemsleyi (the THL value of S. yuana is 23.44 μm, nearly the same as S. hemsleyi) to 50.04 μm in S. dunnii. Two species, S. folgneri and S. hemsleyi have both very small (≤ 1 µm) and small (> 1 µm and ≤ 4 µm) chromosome. The remaining taxa had only small chro- mosome. Two satellites were obser ved in seven subgenus Micromeles taxa, whereas no satellites in two subgenus Aria species. Karyotypes of the analyzed species exhib- it a predominance of metacentric chromosomes with 2–10 submetacentric chromosomes detected in different taxon. Figure 1. Somatic chromosomes at the metaphase stage in root tip cells of Sorbus taxa. A- S. alnifolia; B- S. alnifolia var. angulata; C- S. alni- folia var. lobulata; D- S. dunnii; E- S. folgneri; F- S. hemsleyi; G- S. lushanensis; H- S. ochracea; I- S. yuana. Scale bar = 5 μm. 127Chromosome counts and karyotype analysis of nine taxa in Sorbus subgenera Aria and Micromeles (Rosaceae) The karyotype asymmetry was assessed based on Stebbins classification and 11 different quantitative indi- ces (Table 2). According to the symmetry classification of Steb- bins, S. alnifolia var. alnifolia and S. yuana were classi- fied as category 1A, S. alnifolia var. lobulata and S. fol- gneri as category 2B, the other five taxa as category 2A. For the two species in subgenus Aria, S. hemsleyi and S. yuana, the latter presented the most symmetrical karyotype of all the analyzed species as shown in scat- ter diagram (Figure 3), which with the highest values in Syi% and TF% and the smallest values in the other nine asymmetrical indices (Table 2). Two species in subgenus Aria were more symmetrical than those taxa in sub- genera Micromeles based on two indices A1 and MCA. In general, S. hemsleyi was more asymmetrical than S. yuana with two more submetacentric chromosomes and with values of asymmetrical parameters among the taxa in subgenus Micromeles (Table 2; Figures 3). For subgenera Micromeles, the seven analyzed taxa Figure 2. Haploid idiograms of Sorbus taxa. Red arrows indicate satellites. Scale bar = 5 μm. 128 Yuming Qian et al. displayed considerable differences in karyotypic param- eters (Table 1). The two species: S. dunnii with the small- est values in Syi% and TF% and the highest values in AsK%, CVCI, MCA, A and A1; S. ochracea with the high- est values in CVCL, A2, AI and DI. The most asymmetri- cal karyotype was observed in S. ochracea according to the scatter diagram based on AI and DI (Figures 3B). However, the two species, S. dunnii and S. ochracea, pre- sented the most asymmetrical karyotypes respectively according to different indices as shown in scatter dia- gram based on A1 and A2 (Table 2; Figures 3A, C, D). DISCUSSION The chromosome base number in Sorbus is x = 17, and it is common to all members of Maloideae, Rosace- ae. Four ploidy levels (di-, tri-, tetra- and pentaploid with Figure 3. Scatter plots of studied taxa based on karyotype parameters. A- A1 versus A1; B- AI versus DI; C- CVCI versus CVCL; D- MCA versus CVCL. 129Chromosome counts and karyotype analysis of nine taxa in Sorbus subgenera Aria and Micromeles (Rosaceae) 2n = 34, 51, 68 and approximately 87, respectively) were reported in the genus (Nelson-Jones et al. 2002; Bailey et al. 2008). Only diploids in subgenera Aria and Micromeles were found from China in this and previous studies (Sax 1931; Baranec and Murín 2003), though a large num- ber of polyploidy species (tri-, tetra and pentaploids) appeared in subgenus Aria in Europe (Sennikov and Kurtto 2017). Polyploidy is an important evolutionary mechanism in Sorbus and it is particularly widespread in subgenus Sorbus native to China (McAllister 2005; Li et al. 2021). Whether there are polyploids in subgenera Aria and Micromeles in China, especially in the mountainous area in southwest where a great quantity of polyploidy species were reported from subgenus Sorbus, ploidy-level deter- mination of more species and on more populations are required. Sorbus subgenus Aria is considered the most primi- tive and Micromeles is more derived (Yü and Kuan 1963; Phipps et al. 1990). However, the taxonomic delimitation between Aria and Micromeles is complex. These two sub- genera are easy to distinguish morphologically: Aria spe- cies with a persistent upper part of the hypanthium, and Micromeles species with a deciduous calyx and distinct annular scar at the apex of fruit (Yü and Kuan 1963). However, Micromeles is included within Aria by Rob- ertson et al. (1991) and Aldasoro et al. (2004) based on comprehensive morphological characteristics. A merge (Campbell et al. 2007) or separate (Zhang et al. 2017) of the two is supported by molecular evidence in different phylogenetic studies of Maloideae. Not only the subge- neric concept changed, the delimitation of species varied greatly between authors. For Chinese native subgenera Aria and Micromeles, 20 species out of the total 31 spe- cies and 7 varieties recognized in Flora of China (Lu and Spongberg 2003) were accepted by Aldasoro et al. (2004) in the latest revision of subgenera Aria and Torminaria. In this study, the two subgenera could be distin- guished easily by the existence of satellites. Both the two species of subgenus Aria with much small chromo- somes had more symmetrical karyotype, as showed by MCA and A (Table 1). Not the same as S. yuana, which with all the indices indicating its primitive, S. hems- leyi showed status of taxonomically complicated with values of some parameters among species of subgenus Micromeles. S. hemsleyi was assigned to Micromeles by Yü and Kuan (1963) and was assigned to Aria by Phipps et al. (1990). The inconsistent in values of asymmetry indices just strengthened its complex classification status or a support factor for the merge of the two subgenera need to be further studied. For the limited sampling (two species in Aria and seven taxa in Micromeles), the comparison of karyotype data could not solve the taxonomic problems related to the two subgenera. Whether or which Karyotype param- eters in Sorbus are useful for distinguishing subgenus and species, additional karyotype analysis of a larger number of species are needed. CONCLUSION The chromosome numbers, karyotypes, idiograms and karyotype asymmetry degrees of nine Chinese native taxa in Sorbus subgenera Aria and Micromeles were investigated in this study. The chromosome num- bers (2n = 2x = 34) of eight Chinese endemic taxa were firstly reported. 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