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. 2019 Oct 1;9:14074. doi: 10.1038/s41598-019-50569-3

Genetic Diversity and DNA Fingerprints of Three Important Aquatic Vegetables by EST-SSR Markers

Xingwen Zheng 1,2, Teng Cheng 1, Liangbo Yang 2, Jinxing Xu 2, Jiping Tang 2, Keqiang Xie 2, Xinfang Huang 3, Zhongzhou Bao 4, Xingfei Zheng 1, Ying Diao 5, Yongning You 1,✉, Zhongli Hu 1,✉
PMCID: PMC6773842  PMID: 31575997

Abstract

Twenty-two sacred lotus (Nelumbo nucifera), 46 taros (Colocasia esculenta) and 10 arrowheads (Sagittaria trifolia) were used as materials and combined with EST-SSR (expressed sequence tag-simple sequence repeats) primers developed by our laboratory. Core primers were screened from a large number of primers that were able to distinguish all materials with a high frequency of polymorphisms. Six pairs, twenty pairs and three pairs of core primers were screened from sacred lotus, taro, and arrowhead, respectively. The SSR fingerprints of these three important aquatic vegetables, producing 17-, 87- and 14-bit binary molecular identity cards, respectively, were separately determined by using the core primers. Since there were few core primers of sacred lotus and arrowhead, 3 and 9 primer pairs with higher polymorphic information content (PIC), respectively, were selected as candidate primers. These core and candidate primers were used to identify the purities of No.36 space lotus, Shandong 8502 taro and Wuhan arrowhead, which were 93.3% (84/90), 98.9% (89/90) and 100.0% (90/90), respectively. The fingerprints, displayed as binary molecular identification cards of three important aquatic vegetables, were obtained, and their purity was successfully determined with EST-SSR labeling technology. Phylogenetic trees were also constructed to analyze the genetic diversity of 22 sacred lotus, 46 taros and 10 arrowheads. This study classifies and identifies germplasm resources and is an important reference to test the authenticity and variety purity of other aquatic vegetables in the future.

Subject terms: Plant breeding, Plant molecular biology

Introduction

With their rich nutrients, fantastic flavor and taste, excellent medicinal value and health care functions, aquatic vegetables have been continuously well received by consumers as important economic crops. There are various kinds of aquatic vegetables, of which N. nucifera, C. esculenta and S. trifolia are important and widely planted in China, Southeast Asia, Australia, and Oceania; these aquatic vegetables have high economic value and a long history of cultivation1,2.

SSR fingerprints are inherent in genomes. SSR markers are not affected by external and internal environments, including growth and development time. The advantages of SSR markers are that they are low-cost, fast (within hours), accurate, and reliable. On the one hand, the authenticity of a variety can be effectively identified according to the expected specificity of the DNA fragment. On the other hand, the quality and purity of seeds can be determined by the proportion in the population. Currently, many crop varieties have DNA fingerprints constructed by SSR, such as rice3, corn4, wheat5,6, cotton7, and potato8. In addition, a set of crop varieties have DNA fingerprints constructed based on EST-SSR markers, such as Chinese cabbage9, Cherry10, Hemarthria sibirica11, Blueberry12, Eriobotrya japonica13, and Asparagus14.

The authenticity of the variety and quality and purity of seeds are extremely significant for crop and vegetable production15. However, currently, seed purity identification in China is still dominated by morphological identification16. The method of morphological identification is not only time-consuming and expensive but also subject to environmental factors. Therefore, morphological identification cannot quickly and accurately determine purity or variety. However, identification by SSR markers is accurate, can be accomplished within a short time, is low-cost, and is immune to environmental and self factors. Additionally, EST-SSR markers facilitate easy access to base information and metastasis among related species, with a low cost. Thus, EST-SSR markers have vast potential for future development17.

Due to the limited research on molecular markers, most aquatic vegetables do not have established molecular marker fingerprints or DNA fingerprints constructed from EST-SSR markers. Furthermore, there is no way to identify the authenticity of varieties or the quality and purity of seeds by molecular markers. Therefore, the purpose of this study is to construct DNA fingerprints for aquatic vegetables (sacred lotus, taro and arrowhead) by using a large number of EST-SSR molecular markers developed in our laboratory and to identify the purity of these aquatic vegetables. We aim to provide theoretical knowledge for the construction of DNA fingerprints and purity identification of other aquatic vegetables.

Results and Analysis

Screening of SSR core and candidate primers for three important aquatic vegetables

A total of 11,178 SSR sites were detected by MISA software, and 6,568 pairs of primers were designed by Primer3.0 software. We used a Perl script to synthesize 38 pairs of primers according to electronic polymorphism prediction, and seventy-two pairs of primers were randomly synthesized. Three hundred twenty-five clear bands were obtained by amplifying DNA from 22 scared lotus cultivars with 80 pairs of primers, with an average of 4 bands per pair of primers. From these 80 pairs of primers, 6 pairs of core SSR-labeled primers with polymorphisms that were able to distinguish all 22 materials were selected (Table 1). Three pairs of EST-SSR primers with high PIC (polymorphism information content) were selected as candidate primers for variety purity identification (Table 2). The PIC of each EST-SSR primer pair was calculated using the following formula: PIC=1−(∑i=1nqi2)−(∑i=1n−1∑j=i+1n2qi2qj2), where n is the number of alleles and q is the ith and jth allele frequency18.

Table 1.

Basic information of the six lotus core primers.

Rank Primers Repeats Fragment size range (bp) Number of polymorphic fragments The value of PIC
1 NL-61 (AC)6 212–227 2 0.69
2 NL-28 (AT)6 255–261 3 0.67
3 NL-P8 (TTC)6 153–187 3 0.53
4 NL-35 (GT)6 156–162 3 0.74
5 NL-1 (AGTG)6 242–251 3 0.53
6 NL-P9 (AT)7 180–185 3 0.52
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Table 2.

Basic information of the three lotus candidate primers.

Rank Primers Repeats Fragment size range (bp) Number of polymorphic fragments The value of PIC
1 NL-60 (AG)9 188–210 2 0.19
2 NL-47 (CT)8 225–280 5 0.74
3 NL-P23 (AT)9 248–275 6 0.77
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In total, 5,278 SSR loci were detected by MISA software, and 2,858 pairs of primers were designed by Primer3.0 software. We randomly synthesized 100 pairs of primers. Two hundred thirteen clear bands were obtained by amplifying DNA from 46 taro cultivars with 72 pairs of primers, with an average of 3 bands per pair of primers. From these 72 pairs of primers, 20 pairs of core EST-SSR primers with a polymorphism frequency that could distinguish all 46 taro materials were selected (Table 3).

Table 3.

Basic information of the twenty taro core primers.

Rank Primers Repeats Fragment size range (bp) Number of polymorphic fragments The value of PIC
1 CE-24 (GCT)5 248–275 9 0.80
2 CE-67 (AT)7 152–188 13 0.82
3 CE-8 (GAG)5 273–309 8 0.81
4 CE-19 (TC)8 142–217 7 0.74
5 CE-34 (CT)6 114–142 4 0.67
6 CE-17 (AT)9 193–210 5 0.63
7 CE-98 (CCT)6 206–217 4 0.61
8 CE-84 (TC)6 228–242 4 0.61
9 CE-59 (CGA)5 238–263 3 0.53
10 CE-57 (GGT)5 238–253 4 0.47
11 CE-78 (CTT)6 147–170 2 0.41
12 CE-100 (AG)7 206–231 3 0.40
13 CE-28 (TGC)5 242–273 4 0.36
14 CE-63 (AT)7 105–121 2 0.35
15 CE-2 (CGGTGA)5 180–195 4 0.33
16 CE-37 (CTC)5 276–282 3 0.08
17 CE-45 (CAT)5 191 1 —
18 CE-64 (AT)6 273 1 —
19 CE-27 (GCT)5 105–116 3 0.54
20 CE-47 (GA)7 100–115 3 0.24
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A total of 3,861 SSR loci were detected by MISA software, and 2,476 pairs of primers were designed by Primer3.0 software. We randomly synthesized 100 pairs of primers. One hundred ninety-three clear bands were obtained by amplifying DNA from 10 arrowhead cultivars with 78 pairs of primers, with an average of 2.5 bands per pair of primers. From these 78 pairs of primers, 3 pairs of core EST-SSR primers with a polymorphism frequency that could distinguish all 10 arrowhead materials were selected (Table 4). Nine pairs of EST-SSR primers with high PIC were selected as candidate primers for variety purity identification (Table 5). For every aquatic vegetable, at least one figure of polymorphism showed in supplementary file 2.

Table 4.

Basic information of the three arrowhead core primers.

Rank Primers Repeats Fragment size range (bp) Number of polymorphic fragments The value of PIC
1 SS-50 (GGA)5 171–196 7 0.80
2 SS-86 (AGC)5 270–287 5 0.62
3 SS-84 (TA)7 213–220 2 0.33
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Table 5.

Basic information of the nine arrowhead candidate primers.

Rank Primers Repeats Fragment size range (bp) Number of polymorphic fragments The value of PIC
1 SS-82 (TC)9 135–160 6 0.84
2 SS-62 (GCTG)5 180–189 4 0.75
3 SS-68 (CGA)5 278–290 5 0.72
4 SS-95 (GGA)6 127–136 3 0.67
5 SS-43 (TC)8 250–263 3 0.65
6 SS-41 (GCC)5 192–201 4 0.63
7 SS-93 (CGC)6 222–235 4 0.63
8 SS-88 (TGC)5 186–198 4 0.58
9 SS-80 (CTC)6 142–153 3 0.57
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DNA Fingerprints of three important aquatic vegetables

According to the sequences of the primer alleles presented in Table 4, the scored results, marked as “0” and “1” for the SSR molecular marker bands of sacred lotus core primers, were counted into binary data as 17-bit binary molecular identity cards of 22 sacred lotus cultivars (Table 6).

Table 6.

Binary molecular identity of twenty-two lotus varieties.

Rank Name Binary molecular identity card Rank Name Binary molecular identity card
1 Cunsan lotus 01100101001101010 12 Wufei lotus 10001110010110011
2 Furong lotus 10100101001001100 13 Zhuoshang lotus 10001100010101010
3 Baixiang lotus 10100101010001100 14 Jiande red flower lotus 10001001010001010
4 Hongxiang lotus 10100101010011100 15 Yixian lotus 10001011010011010
5 Chuzhou white lotus 10010001001001110 16 Qiushui changtian lotus 10001101100101000
6 Tuxuan lotus 10010101001001100 17 Chongtai lotus 10001101010101011
7 White flower jian lotus 10010101001001110 18 Donggua lotus 10001001100001100
8 Red flower jianlotus 01010100001100010 19 No.36 space lotus 10001101010001100
9 Baiye lotus 01001101010001100 20 Riza lotus III-1 10001100010001101
10 Jingguanglotus II 10001101001001100 21 Riza lotus III-2 01001100010001101
11 Star peony 01010100010100010 22 Wuzhi lotus II 01001101001100010
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According to the sequences of the primer alleles presented in Table 5, the scored results, marked as “0” and “1” for the SSR molecular marker bands of taro core primers, were counted into binary data as 87-bit binary molecular identity cards of 46 taro cultivars (Table 7).

Table 7.

Binary molecular identity of forty-six taro varieties.

Rank Name Binary molecular identity card
1 Qionglai red-billed taro 010001101000010001000010010000000000001010011111100101010000101111100000011000000110001
2 Xinjin white-billed taro 010011110000010001010010010000001110111011011111001101100000101110010100010000100101001
3 Renshou Wuganqiang taro 010011110000010001010010010000001110111011111111001101100000101110010100010000100101001
4 Pengshan black stem taro 010011110000010001011010010000001100001000011111001010100000101111010000011000000110001
5 Jiange red stem taro 010011110000010001010010010000000000111011011111001101100000101110010100010000100101001
6 Dayi dryland taro 010011101000010001000010010000000010101010011111100011010000101111100000011000000101001
7 Longmen dryland taro 010011110000010001000010110000001110111011111111001101100000101110010100010000100101001
8 Tongji dark stem taro 010011110000010001010010110001001110111011111111001101100000101110010100010000100101001
9 Chengbei Jintang taro 010011110000010001010010110000001110111011011100001101100000101110010100010000100101001
10 Baoning taro 010011110010110010010101000100001101111110011100100101001010100111001011010010001101001
11 Baiqiao Jintang taro 010011110000010001000010110000000000001000011100001101100000101110010100010000100101001
12 Baoning red stem taro 010011110000010001010010110001001110111011111100001101100000101110010100010000100101001
13 Saijin taro 010011101010110001010010010001000000001010011100100011010000101111101000011000000110001
14 Xingwen dryland taro 010011110000010001010010110000001110111011111100001101100000101110010100010000100101001
15 Huilong taro 010011110010010010010101000100001101111110111100100101001010100011001011010010001101001
16 Chengxi cyan stem taro 010011110000010001010010110001001110111011111100001101100000101110010100010000100110001
17 Yongan Wuganqiang taro 010011110010110010010101000100001101111110111100100101001010100111001011010010001101001
18 Dazhu taro 010011110100010001010010110001001110111011111100001101100000101110010100010000100101001
19 Dongxiang red stem taro 010111110100010001010010110001001110111011111100001101100000101110010100010000100101001
20 Taihe red taro 010101110000010001000010110000001110111011111100001101100000101110010100010000100101001
21 Gongping black stem taro 010111110000010001010010110000001110111011111100001101100000100110010100010000100101001
22 Lantian taro 010111110000010001011010010000001100011000111100001010100000101111010000011000000110011
23 Qionglai black stem taro 010111110000010001010010110001001110111011111100001101100000101110010100010000100101001
24 Jintang Wujiaoqing taro 010111110000010001000010110000001110111011111100001101100000101110010100010000100101001
25 Shuangliu wetland taro 010111110010110010010101000100000001111110111100100101001010100011001011010010001101001
26 Yumen Tangbao taro 010111110001011001000010010000001110101000011100100011010001001111010000010000010110001
27 Xinchang betelnut taro 010111101000010001010010010000000010101010011100100011010000101111010000011000000101001
28 Lipu taro 010111110001011001000010010000001110101000011100100011100000101111010000010000010110001
29 Sichuan head taro I 010111110000010001011010010001001100001000111100011010100000101111010000011000000110011
30 Wanxing head taro 010111110000010000011010110001000110101001111100001001001000100110011001010001001101111
31 Lujing big taro 010111110010010100011010110001000110101001111100001001001000100110011001010001001101111
32 Zhongpa head taro 010111110000010001000010010001001110101000011100100011100000100111010000010000010110001
33 Yugan head taro 010111110010010100011010110000000110101001111100001001001000100111010001010001001101111
34 Qingfeng head taro 010111110010010100011010110000000110101001111100001001001000101111001001010001001101111
35 Jiangan Baba taro 010111110100010001110010010001000001111010111100001100100000111111010100110000100110001
36 Dongxiang Goutou taro 010111110100010001110010010001000001111010111100011000100000111111010100110000100110001
37 Ezhou taro 010111110010010010010101000100001101111110111100100101001010100111001011010100001101001
38 WHU greenhouse taro 010011110010010010010101000101001101111110111100100101001010100111001011010010001101001
39 WHU market taro 010011100100010001110010001101110010111110111100100101100000101110000100010000001110001
40 Shandong 8502 taro 010011110100010001110010001101110010111110111100100101100000101110001000000000101100001
41 Zhifang taro 010011110000010001010010001101001110111011011100001101100000101110010100000000100000001
42 WHU private plot taro 010000110010010010010101000100001101111110111100100101001010100111001000000010001101000
43 Paizhong taro 010011110010010010010101000100001101111110111100100101001010100111001000000010001101000
44 Zhuji taro 010011110010010010010101000100001101111110111100100101001010100111001000000010001101001
45 Zuonao Maliuyuan taro 010011110000010001010010001100001110111011111100001101100000100110010100000000100110001
46 Tangxun lake village taro 101011110010010010010000010010001101101110111100100101001010100010011000000000001110000
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According to the sequences of the primer alleles presented in Table 6, the scored results, marked as “0” and “1” for the SSR molecular marker bands of arrowhead core primers, were counted into binary data as 14-bit binary molecular identity cards of 10 arrowhead cultivars (Table 8).

Table 8.

Binary molecular identity of ten arrowhead varieties.

Rank Name Binary molecular identity card Rank Name Binary molecular identity card
1 Baoying ziyuan arrowhead 00001100101001 6 Shengdang II arrowhead 00001000010011
2 Gaoyou great white arrowhead 00010010100011 7 Kunming arrowhead 10001000010011
3 Jiangxing produce shendang arrowhead 00001000110011 8 Guangxi sand arrowhead 00001001010001
4 Suzhou yellow arrowhead 00001000110001 9 Guangzhou arrowhead 00001010001001
5 Ziyuan II arrowhead 01000100110011 10 Wuhan arrowhead 00101000010101
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Variety purity identification of three important aquatic vegetables

Among 90 samples of the No.36 space lotus, the bands of 84 samples were regarded as the same characteristic band of the cultivar. The other 6 samples judged to be different cultivars were compared with the characteristic band. Three samples of differential alleles had eight bands, and the other 3 samples had one band. The purity of No.36 space lotus was 93.3% (84/90).

Among 90 samples of Shangdong 8502 taro, the bands of 89 samples were regarded as the same characteristic band of the cultivar. The remaining sample judged to be a different cultivar with 4 differential alleles was compared with the characteristic band. The purity of Shangdong 8502 taro was 98.9% (89/90).

The bands of all 90 Wuhan arrowhead samples were regarded as the same characteristic band of the cultivar, so the 90 samples were identified as the same variety. The purity of Wuhan arrowhead was 100% (90/90).

Genetic diversity analysis of three important aquatic vegetables

A phylogenetic tree of three important aquatic vegetables was constructed (Fig. 1). The Jaccard similarity coefficient ranged from 0.50 to 0.99. Twenty-two individual plants were separated into three major groups, I, II, and III, at a Jaccard similarity coefficient level of 0.65 in sacred lotus (Fig. 1A). The results showed that there was genetic differentiation between lotus with flowers and lotus with roots; lotus with roots was concentrated in group I, while lotus with flowers was mainly concentrated in group III. Forty-six taros were separated into four major groups at a Jaccard similarity coefficient level of 0.74 (Fig. 1B). Two multi-headed taro Jiangan Baba taro and Dongxiang Goutou taro were clustered together, which indicated that there was obvious genetic differentiation between multi-headed and other taro cultivars. Some head taros clustered together in group III, and some clustered together with other types of materials; more than half of the multi-cormels taros were clustered in group II. Arrowhead was separated into two groups (Fig. 1C). A dendrogram with a scale from 0.70 to 0.98 based on Jaccard’s similarity coefficient was constructed and clearly separated the 8 accessions from Jiangsu and Zhejiang provinces into 4 main clusters, while the remaining Guangxi sand arrowhead and Guangzhou arrowhead were classified into group II.

Figure 1.

Figure 1

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Dendrogram showing the genetic relationships of three important aquatic vegetables. (A) Genetic relationships among 22 individual sacred lotus plants based on EST-SSR markers. (B) Genetic relationships among 46 individual taros based on EST-SSR markers. (C) Genetic relationships among 10 arrowheads based on EST-SSR markers.

Discussion

DNA fingerprints are generally constructed by three methods: the characteristic locus method, the single primer method and the core primer combination method, the most efficient of which is the core primer combination method4,19–22. Core primers can play important roles in preliminary research, generally leading to a good polymorphism frequency, stability, reproducibility and discriminability. Identifying the the core primers of sacred lotus, taro and arrowhead is a key step for SSR fingerprint construction and purity identification, and it is also a prerequisite for the commercial application of SSR fingerprints. In this study, polymorphic SSR primers were first screened as alternative primers, and a set of SSR primers were found to be the core primers for these germplasm resources, with the smallest number that could completely distinguish all germplasm resources. According to the expansion and complexity of samples and genomes, the number of core primers should be adjusted accordingly. For variety identification, it is better to identify more samples with fewer primers; therefore, the ideal method is to distinguish the most varieties with a single primer. However, this was difficult to achieve, even in arrowhead, the cultivar with the smallest number. As a result, the core primer combination method was adopted in this study to construct fingerprints. In this study, 6 core primers and 3 candidate primers were selected for sacred lotus, 20 core primers for taro, and 3 core primers and 9 candidate primers for arrowhead. Then, 17-, 87- and 14-bit binary molecular identification cards were successfully constructed for 22 sacred lotus cultivars, 46 taro cultivars and 10 arrowhead cultivars, respectively. The DNA fingerprint of sacred lotus was more useful than those of the others23,24. The construction of SSR fingerprints for these three important aquatic vegetables is still in its infancy, and in particular, SSR fingerprints for taro and arrowhead have not been reported. SSR fingerprints were constructed by the core primers combination method, which provides useful methodological guidance for the construction of a standard DNA fingerprint database and performing aquatic vegetable mapping analysis in the future.

As a kind of molecular marker with the advantages of high allelic variation, codominance, simple and rapid detection, and good stability, SSRs have been maturely applied in many regions, such as genetic diversity analysis, fingerprint construction, trait marker and genetic linkage map construction. Many agronomists and geneticists have carried out extensive research and application of SSRs25. For example, 30 pairs of core primers were used to construct a fingerprint and test the authenticity and purity of Zhongmian Institute 63 cotton. Compared with field trial identification, the results showed that 30 pairs of core primers achieved good identification26. From 36 pairs of primers, 3 core primers, MCPI-5, MCPI-16 and MCPI-17, were selected. Identified by MCPI-5 and MCPI-16, the purity of 267 watermelon T-1 hybrids was 97.75%, consistent with the field morphological identification results. Hence, the core primers selected could be used for purity identification of watermelon T-1 hybrids27. Other crops, such as rice28, rape29, potato30, maize31, eggplant32,33, cabbage34,35, and soybean36, have also been able to be identified.

EST-SSR markers are new molecular markers based on the expression of sequence tag data combined with the characteristics of SSR. These markers combine the dual advantages of SSR and EST and expand the application prospects of SSR. In 2009, EST-SSR markers were applied to the identification of safflower purity, which became the first successful example of the use of EST-SSR markers for purity identification of a crop hybrid population37. Subsequently, studies of the purity identification of rice, cabbage, melon (cucumber, melon, watermelon) and other crops have been carried out. The results showed that EST-SSR markers are superior and more sensitive than plant morphology identification in the field, and the purity of detection is generally 2–3% higher than the results from the field34,38–40. However, the most commonly used method for the authenticity and purity detection of aquatic vegetables is still morphological identification, which is accomplished by comparison with standard morphological characteristics or determination of morphological characteristic consistency in tested varieties. Due to the limited molecular genetics research, there are a few available SSR markers and no reports of the use of EST-SSR markers to detect the authenticity and purity of aquatic vegetables. Therefore, based on lotus, taro and arrowhead cultivars from all over China, the purity of No.36 space lotus, Shandong 8502 taro and Wuhan arrowhead was determined by EST-SSR and core primer PCR amplification. The purities of these three cultivars were 93.3%, 98.9% and 100%, respectively. It can be seen that these varieties all developed with rigorous breeding and screening. With less genetic variation and higher consistency, the three important aquatic vegetables were close to sacred lotus, taro and arrowhead pure varieties. Because of the genetic differentiation in this cultivar, No.36 space lotus with lower purity is a hybrid cultivar.

In this study, the genetic relationship of a lotus germplasm resources is not related to its geographical origin, as reported in previous reports41. At present, lotus can be divided into three types according to its morphological characteristics and its main parts, namely, lotus with seeds, lotus with flowers and lotus with roots41–43. The differentiation of lotus with roots and lotus with flowers in this study was consistent with previous research44. There is a certain correlation between the genetic relationship and phenotypic traits of lotus. This type of diversity evaluation will provide important reference materials for breeding research of these cultivars in the future. Forty-six taros were separated into four major groups. The main branches were a mixture of materials from different regions and types, and this result indicated that there is no obvious correlation between morphological characteristics or geographic distribution and kinship, possibly due to the cultivar classification of taro based on the variation of its morphological characteristics, which was probably caused by mutations of a few major genes. There is a certain correlation between the regional differentiation of arrowhead cultivars and their genetic differentiation. In Jiangsu and Zhejiang provinces, which belong to the Yangtze River basin, there is a certain differentiation of arrowhead cultivars, and the results of this study suggest that arrowhead is limited by region, especially water limitation. Lower gene exchange led to abundant genetic diversity, which was beneficial to arrowhead breeding. This study can server as a significant reference for the authenticity and purity detection of aquatic vegetable cultivars. Moreover, EST-SSR markers have higher species transferability45 and can also be used to study other related species.

Materials and Methods

Plant materials

Twenty-two sacred lotus cultivars were used to construct SSR fingerprints, including 14 sacred lotus with seeds cultivars, 7 sacred lotus with flowers cultivars and 1 sacred lotus with root cultivar (Table 9). Forty-six taro cultivated varieties (Table 10) and 10 arrowhead cultivars (Table 11) were used to construct SSR fingerprints.

Table 9.

Twenty-two lotus varieties used in this study.

Rank Name Category Source Rank Name Category Source
1 Cunsan lotus** Lotus with seeds Xiangtan, Hunan 12 Wufei lotus** Lotus with flowers Beijing
2 Furong lotus Lotus with seeds Xiangtan, Hunan 13 Zhuoshang lotus Lotus with flowers Beijing
3 Baixiang lotus Lotus with seeds Xiangtan, Hunan 14 Jiande red flower lotus Lotus with flowers Jiande, Zhejiang
4 Hongxiang lotus Lotus with seeds Xiangtan, Hunan 15 Yixian lotus Lotus with flowers Nanjing, Jiangsu
5 Chuzhou white lotus Lotus with seeds Jinhua, Zhejiang 16 Qiushui changtian lotus Lotus with flowers Guangchang, Jiangxi
6 Tuxuan lotus Lotus with seeds Jinhua, Zhejiang 17 Chongtai lotus Lotus with flowers Wuhan, Hubei
7 White flower jian lotus** Lotus with seeds Jianning, Fujian 18 Donggua lotus** Lotus with flowers Changsha, Hunan
8 Red flower jianlotus Lotus with seeds Jianning, Fujian 19 No.36 space lotus* Lotus with seeds Guangchang, Jiangxi
9 Baiye lotus Lotus with seeds Guangchang, Jiangxi 20 Riza lotus III-1 Lotus with seeds Wuhan, Hubei
10 Jingguanglotus II Lotus with seeds Guangchang, Jiangxi 21 Riza lotus III-2 Lotus with seeds Wuhan, Hubei
11 Star peony Lotus with seeds Guangchang, Jiangxi 22 Wuzhi lotus II** lotus with root Wuhan, Hubei
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*90 materials for purity identification, **Control sample for purity identification.

Table 10.

Forty-six taro varieties used in this study.

Rank Name Category Area Rank Name Category Area
1 Qionglai red-billed taro Taro with multi-cormels Yangan, Qionglai, Sichuan 24 Jintang Wujiaoqing taro Taro with multi-cormels Qingjiang, Jintang, Sichuan
2 Xinjin white-billed taro Taro with multi-cormels Wanxing, Xinjin, Sichuan 25 Shuangliu wetland taro Taro with multi-cormels Jitian, Shuangliu, Sichuan
3 Renshou Wuganqiang taro Taro with multi-cormels Shigao, Renshou, Sichuan 26 Yumen Tangbao taro** Taro with multi-cormels Yumen, Yanbian, Sichuan
4 Pengshan black stem taro Taro with multi-cormels Pengshan, Sichuan 27 Xinchang betelnut taro Head taro Xinchang, Dayi, Sichuan
5 Jiange red stem taro Taro with multi-cormels Jiange, Guangyuan, Sichuan 28 Lipu taro Head taro Jiangyang, Luzhou, Sichuan
6 Dayi dryland taro ** Taro with multi-cormels Anren, Dayi, Sichuan 29 Sichuan head taro I Head taro Chengdu, Sichuan
7 Longmen dryland taro Taro with multi-cormels Longmen, Mianyang, Sichuan 30 Wanxing head taro Head taro Wanxing, Xinjin, Sichuan
8 Tongji dark stem taro Taro with multi-cormels Tongji, Zhongjiang, Sichuan 31 Lujing big taro Head taro Lujing, Yingshan, Sichuan
9 Chengbei Jintang taro Taro with multi- cormels Chengbei, Jiange, Sichuan 32 Zhongpa head taro Head taro Zhongpa, Yuechi, Sichuan
10 Baoning taro Taro with multi-cormels Baoning, Langzhong, Sichuan 33 Yugan head taro** Head taro Yugan, Yanbian, Sichuan
11 Baiqiao Jintang taro Taro with multi-cormels Baiqiao, Cangxi, Sichuan 34 Qingfeng head taro Head taro Qingfeng, Jianyang, Sichuan
12 Baoning red stem taro Taro with multi-cormels Baoning, Langzhong, Sichuan 35 Jiangan Baba taro Multi-headed taro Jiangan, Yibin, Sichuan
13 Saijin taro Taro with multi-cormels Saijin, Yilong, Sichuan 36 Dongxiang Goutou taro** Multi-headed taro Dongxiang, Yihan, Sichuan
14 Xingwen dryland taro Taro with multi-cormels Xingwen, Bazhou, Sichuan 37 Ezhou taro** Taro Ezhou, Hubei
15 Huilong taro Taro with multi-cormels Huilong, Yingshan, Sichuan 38 WHU greenhouse taro Taro Wuhan University, Hubei
16 Chengxi cyan stem taro Taro with multi-cormels Chengxi, Dazhu, Sichuan 39 WHU market taro Taro Wuhan University, Hubei
17 Yongan Wuganqiang taro Taro with multi-cormels Yongan, Gaoping, Sichuan 40 Shandong 8502 taro * Taro Shandong
18 Dazhu taro Taro with multi-cormels Dazhu, Daxian, Sichuan 41 Zhifang taro Taro Zhifang, Jiangxia, Hubei
19 Dongxiang red stem taro Taro with multi-cormels Dongxiang, Xuanhan, Sichuan 42 WHU private plot taro Taro Wuhan University, Hubei
20 Taihe red taro Taro with multi-cormels Taihe, Shehong, Sichuan 43 Paizhong taro Taro Paizhong, Xiantao, Hubei
21 Gongping black stem taro Taro with multi-cormels Gongping, Zizhong, Sichuan 44 Zhuji taro Taro Zhuji, Xiantao, Hubei
22 Lantian taro Taro with multi-cormels Jiangyang, Luzhou, Sichuan 45 Zuonao Maliuyuan taro Taro Louhe, Xiantao, Hubei
23 Qionglai black stem taro Taro with multi-cormels Qionglai, Sichuan 46 Tangxun lake village taro Taro Hongshan, Wuhan, Hubei
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*90 materials for purity identification, ** Control sample for purity identification.

Table 11.

Ten arrowhead varieties used in this study.

Rank Name Category Area
1 Baoying ziyuan arrowhead Ziyuan arrowhead Baoying, Jiangsu
2 Gaoyou great white arrowhead** Great white arrowhead Gaoyou, Jiangsu
3 Jiangxing produce shendang arrowhead Shendang arrowhead Jiangxing, Zhejiang
4 Suzhou yellow arrowhead Suzhou yellow arrowhead Suzhou vegetable research institute, Jiangsu
5 Ziyuan II arrowhead** Ziyuan arrowhead Suzhou vegetable research institute, Jiangsu
6 Shengdang II arrowhead Shengdang arrowhead Suzhou vegetable research institute, Jiangsu
7 Kunming arrowhead** Kunming arrowhead Kunming, Yunnan
8 Guangxi sand arrowhead** Guangxi sand arrowhead Baipeng, Liujiang, Guangxi
9 Guangzhou arrowhead** Guangzhou arrowhead Guangzhou, Guangdong
10 Wuhan arrowhead* Wuhan arrowhead Wuhan University, Hubei
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*90 materials for purity identification, **Control sample for purity identification.

Extraction of genomic DNA from three important aquatic vegetables

From the above young leaves of these materials, genomic DNA46 was extracted by the modified CTAB method. Among the materials listed above, genomic DNA from the varieties used for purity identification was collected and extracted from the young leaves of 90 plant samples. DNA was extracted by 1.0% agarose gel electrophoresis and stored at −20 °C for later use.

Primer amplification

SSR marker detection was performed using a Perl program known as MicroSatellite (MISA, http://pgrc.ipk-gatersleben.de/misa) from the S. sagittifolia transcriptome, C. esculenta transcriptome and N. nucifera transcriptome. Using effective EST-SSR primers developed in our laboratory, genomic DNA was amplified by PCR. The primer sequences for sacred lotus and arrowhead are shown in supplementary file 1. Based on the obtained bands, EST-SSR markers were selected as the core primers with a high polymorphism frequency that could distinguish all cultivars. These core primers were employed to amplify each of the 90 samples and 5 control samples of genomic DNA of No.36 space sacred lotus, Shandong 8502 taro, and Wuhan arrowhead. Because of the lack of core primers for sacred lotus and arrowhead, 3 and 9 pairs of candidate primers were added to the samples. The reaction mixture (15 μL) contained 1.5 μL of buffer (10 × dilution), 0.8 μL of MgCl2 (20 mM), 0.6 μL of dNTP (10 mM), 0.5 μL of TaqDNA polymerase, 1 μL of forward primer (10 μM), 1 μL of reverse primer (10 μM), 2 μL of template DNA and 7.6 μL of ddH2O. The amplification conditions included an initial denaturation step at 94 °C for 5 min, followed by 35 cycles of denaturation at 94 °C for 30 s, and annealing extension at 54–65 °C, elongation at 72 °C for 30 s and a final step at 72 °C for 5 min. Ten microliters of PCR bromophenol blue buffer was added to the PCR products and placed in the gene amplification instrument (BIOER co.,LTD., Hangzhou, China) at 94 °C to degenerate for 5 min, then quickly cooled on ice and tested with a polyacrylamide gel. The silver staining method was used to display the color, and the electrophoresis results were observed on a slide lamp.

Data statistics and analysis

According to the polyacrylamide electrophoresis results, a band of the same fragment size was recorded as a marker allele and scored as 1, 0 and 2 for a band, no band and a deletion, respectively. The EST-SSR locus allelic variation was counted for sacred lotus, taro and arrowhead, and the statistical data were input into a computer. Data analyses were performed by using the NTSYSpc package version 2.147. The SSR markers were identified as core primers with indicated polymorphisms that could distinguish all cultivars. A set of binary data were obtained from the “0” and “1” data produced by these markers as the binary molecular identity cards of these cultivars.

The characteristic band of a variety is the common characteristic band of most sample individuals. The band of each sample was compared with the characteristic band, and different allele numbers between cultivars (>1) were determined to indicate different varieties, while (=0) was determined to indicate the same variety. P = X/Y × 100%, where X is the number of individuals of the same variety, Y is the total number of individuals identified and P is the value of purity.

Supplementary information

Supplementary file (239.5KB, pdf)

Acknowledgements

This research was supported by National Key Technologies R&D Program (No. 2012BAD27B01).

Author Contributions

X. Zheng designed and performed the experiments, analyzed the results, drew the figures and wrote. the manuscript. T. Cheng worked on some experiments. L. Yang, J. Xu, J. Tang, K. Xie and Z. Bao provided some materials. X. Zheng, X. Huang and Y. Diao provided some scientific advice and corrections. Y. You and Z. Hu analyzed the results and approved the final manuscript. All authors have read and approved the manuscript in its final form.

Competing Interests

The authors declare no competing interests.

Footnotes

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Yongning You, Email: shangruzhenren@163.com.

Zhongli Hu, Email: huzhongli@whu.edu.cn.

Supplementary information

Supplementary information accompanies this paper at 10.1038/s41598-019-50569-3.

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Supplementary file (239.5KB, pdf)

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