Lotus is in the family Nelumbonaceae, which consists of only one genus with two species, Nelumbo nucifera and Nelumbo lutea (Kanazawa et al., 1998; Savolainen and Chase, 2003). Nelumbo nucifera is found throughout Asia and Australia. In China, N. nucifera is distributed on both sides of the major freshwater lakes in the valleys of the Yangtze River, Yellow River, and Pearl River. Nelumbo lutea is distributed across North America and northern South America but grows mainly in the eastern and central United States (Borsch and Wilhelm, 1994). Although these two species differ in external morphology such as plant size, leaf shape, petal shape, and color, as a result of their geographical isolation, they share the same number of chromosomes (2n = 16) and the similar karyotype and can be hybridized easily. It has been proposed that N. lutea should be considered a subspecies of N. nucifera (Huang et al., 1992). However, other scholars consider the two taxa to be separate species in the genus Nelumbo (Chen et al., 2008; Han et al., 2007a, 2007b, 2009; Kubo et al., 2009; Li et al., 2010; Tian et al., 2008b).
Nelumbo nucifera is an important ornamental aquatic plant with beautiful flowers and unusual leaves (Ni and Zhao, 1987; Wang and Zhang, 2005). It is also a source of herbal medicine with strong antipyretic, cooling, astringent, and demulcent properties, which can be attributed to alkaloids and flavonoids in the leaves, leaf stems, and rhizomes (Mukherjee et al., 1997; Qian, 2002; Sinha et al., 2000). Nelumbo lutea is a species as magnificent as N. nucifera, but it is cultivated less commonly as an ornamental plant. It is considered to be an invasive, difficult-to-eradicate weed in its original habitat (Borsch and Wilhelm, 1994; Wiersema, 1997) and probably originally confined to flood plains of major rivers and their tributaries in the east–central United States and carried northward and eastward by aborigines who used the seeds and tubers for food. The rhizome and seeds of N. lutea are commonly eaten by Native Americans, and those of N. nucifera are still a part of the Oriental diet. In Japan, the lotus has been cultivated as an ornamental and food plant since it was introduced from China 1000 years ago (Masuda et al., 2006). Approximately 350 cultivars of lotus are known in Japan, including more than 100 landraces (Kubo et al., 2009).
In China, the lotus has been cultivated for more than 3000 years, and rich germplasm resources have been generated by artificial hybridization and selection (Ni and Zhao, 1987; Wang and Zhang, 2005). More than 600 lotus cultivars have been recorded in China and have been classified into three main types on the basis of their morphological characteristics and agricultural properties: 1) flower lotus; 2) seed lotus; and 3) rhizome lotus (Wang and Zhang, 2005; Zou et al., 1997). The flower lotus cultivars have been subdivided further on the basis of petal characteristics into several types, which include: 1) few-petaled lotus, with less than 24 petals per flower; 2) double-petaled lotus, in which most of the stamens have been transformed into petals; 3) duplicated-petaled lotus, in which pistils have been transformed into petals or bubbled; 4) versicolor lotus, with red strips or blocks dotted on the white petal; and 5) thousand-petaled lotus, in which the stamens, pistils, and receptacles have all been transformed into petals (Wang and Zhang, 2005). However, such characteristics might not be useful for classification because of their continuous variation and high degree of plasticity in response to changes in environmental conditions. In light of these limitations, further analysis of the genetic differences among lotus cultivars by molecular methods is necessary.
In recent years, the rapid development of molecular marker technologies and DNA fingerprinting analysis has provided new techniques to assess the genetic diversity of plants and animals such as random amplified polymorphic DNA (RAPD), AFLPs, intersimple sequence repeats (ISSRs), and simple sequence repeats (SSRs) (Ge et al., 2005; Oraguzie et al., 2001; Torres-Díaz et al., 2007; Wang et al., 2011). These approaches have also been used to analyze the genetic diversity of the lotus (Chen et al., 2008; Guo et al., 2007; Han et al., 2007a, 2007b, 2009; Kubo et al., 2009; Li et al., 2010; Pan et al., 2007, 2010; Tian et al., 2008a, 2008b) and have revealed rich genetic variation in lotus germplasm. Although AFLP markers are dominant in most cases, they can detect more variation at the whole genome level than ISSR or RAPD markers and are more efficient, because large numbers of loci can be screened readily (Na et al., 2009; Portis et al., 2005). At present, only one study that used AFLP markers to evaluate the genetic diversity of rhizome lotuses has been published (Peng et al., 2004). However, the limited number of AFLP markers (two pairs) and lotus accessions (12 rhizome lotuses) that were used was not sufficient to assess the genetic variation of the lotus.
In the study reported here, 11 AFLP primer pairs were selected to evaluate the genetic diversity and relationships among 138 lotus accessions. The accessions represented a large collection of genotypes of the two species (N. lutea and N. nucifera): flower lotuses, seed and rhizome cultivars, ancient lotuses, Japanese cultivars, and tropical lotuses. The objectives were to: 1) evaluate the genetic relationship between N. nucifera and N. lutea; 2) assess the genetic diversity among flower, seed, and rhizome lotuses; and 3) confirm which morphological characteristics can be used in the classification of lotuses.
Borsch, T. & Wilhelm, B. 1994 Classification and distribution of the genus Nelumbo Adans (Nelumbonaceae) Beitrage zur Biologie der Pflanzen 68 421 450
Chen, Y.Y., Zhou, R.C., Lin, X.C., Wu, K.Q., Qian, X.E. & Huang, S.Z. 2008 ISSR analysis of genetic diversity in sacred lotus cultivars Aquat. Bot. 89 311 316
Ge, X.J., Yu, Y., Yuan, Y.M., Huang, H.W. & Yan, C. 2005 Genetic diversity and geographic differentiation in endangered Ammopiptanthus (Leguminosae) populations in desert regions of northwest China as revealed by ISSR analysis Ann. Bot. (Lond.) 95 843 851
Guo, H.B., Li, S., Peng, J. & Ke, W. 2007 Genetic diversity of Nelumbo accessions revealed by RAPD Genet. Resources Crop Evol. 54 741 748
Han, Y.C., Teng, C.Z., Chang, F.H., Robert, G.W., Zhou, M.Q., Hu, Z.L. & Song, Y.C. 2007a Analyses of genetic relationships in Nelumbo nucifera using nuclear ribosomal ITS sequence data, ISSR and RAPD markers Aquat. Bot. 87 141 146
Han, Y.C., Teng, C.Z., Wahiti, G., Zhou, M.Q., Hu, Z.L. & Song, Y.C. 2009 Mating system and genetic diversity in natural populations of Nelumbo nucifera (Nelumbonaceae) detected by ISSR markers Plant Syst. Evol. 277 13 20
Han, Y.C., Teng, C.Z., Zhong, S., Zhou, M.Q., Hu, Z.L. & Song, Y.C. 2007b Genetic variation and clonal diversity in populations of Nelumbo nucifera (Nelumbonaceae) in central China detected by ISSR markers Aquat. Bot. 86 69 75
Huang, X.Q., Chen, J.Y. & Huang, G.C. 1992 Preliminary studies on biosystematical relationship between the two Nelumbo species Acta Hort. Sinica 19 164 170
Kanazawa, A., Watanabe, S., Nakamoto, T., Tsutsumi, N. & Hirai, A. 1998 Phylogenetic relationships in the genus Nelumbo based on polymorphism and quantitative variations in mitochondrial DNA Genes Genet. Syst. 73 39 44
Kubo, N., Hirai, M., Kaneko, A., Tanaka, D. & Kasumi, K. 2009 Classification and diversity of sacred and American Nelumbo species: The genetic relationships of flowering lotus cultivars in Japan using SSR markers Plant Genet. Resources 7 260 270
Li, Z., Liu, X., Gituru, R.W., Juntawong, N., Zhou, M. & Chen, L. 2010 Genetic diversity and classification of Nelumbo germplasm of different origins by RAPD and ISSR analysis Sci. Hort. 125 724 732
Masuda, J.I., Urakawa, T., Ozaki, Y. & Okubo, H. 2006 Short photoperiod induces dormancy in lotus (Nelumbo nucifera) Ann. Bot. (Lond.) 97 39 45
Mukherjee, P.K., Saha, K., Das, J., Pal, M. & Saha, B.P. 1997 Studies on the antiinflammatory activity of rhizomes of Nelumbo nucifera Planta Med. 63 367 369
Na, A., Guo, H.B. & Ke, W.D. 2009 Genetic variation in rhizome lotus (Nelubmo nucifera Gaertn. ssp. nucifera) germplasm from China assessed by RAPD markers Agr. Sci. China 8 31 39
Oraguzie, N.C., Gardiner, S.E., Basset, H.C.M., Stefanati, M., Ball, R.D., Bus, V.G.M. & White, A.G. 2001 Genetic diversity and relationships in Malus sp. germplasm collections as determined by randomly amplified polymorphic DNA J. Amer. Soc. Hort. Sci. 126 318 328
Pan, L., Quan, Z., Li, S., Liu, H., Huang, X., Ke, W. & Ding, Y. 2007 Isolation and characterization of microsatellite markers in the sacred lotus (Nelumbo nucifera Gaertn.) Mol. Ecol. Notes 7 1054 1056
Pan, L., Xia, Q., Quan, Z., Liu, H., Ke, W. & Ding, Y. 2010 Development of novel EST-SSRs from sacred Lotus (Nelumbo nucifera Gaertn) and their utilization for the genetic diversity analysis of N. nucifera J. Hered. 101 71 82
Peng, Y.L., Han, Y.C., Wang, L., Teng, C.Z., Zhou, M.Q., Hu, Z.L. & Song, Y.C. 2004 Genetic diversity in lotus (Nelumbo) accessions revealed by AFLP technique Mol. Plant Breed. 2 823 827
Portis, E., Barchi, L., Acquadro, A., Macua, J.I. & Lanteri, S. 2005 Genetic diversity assessment in cultivated cardoon by AFLP (amplified fragment length polymorphism) and microsatellite markers Plant Breed. 124 299 304
Pritchard, J.K., Stephens, M. & Donnelly, P. 2000 Inference of population structure using multilocus genotype data Genetics 155 945 959
Qian, J.Q. 2002 Cardiovascular pharmacological effects of bisbenzylisoquinoline alkaloid derivatives Acta Pharmacol. Sin. 23 1086 1092
Sinha, S., Mukherjee, P.K., Mukherjee, K., Pal, M., Mandal, S.C. & Saha, B.P. 2000 Evaluation of antipyretic potential of Nelumbo nucifera stalk extract Phytother. Res. 14 272 274
Tian, H.L., Chen, X.Q., Wang, J.X., Xue, J.H., Wen, J., Mitchell, G. & Zhou, S.L. 2008a Development and characterization of microsatellite loci for lotus (Nelumbo nucifera) Conserv. Genet. 9 1385 1388
Tian, H.L., Xue, J.H., Wen, J., Mitchell, G. & Zhou, S.L. 2008b Genetic diversity and relationships of lotus (Nelumbo) cultivars based on allozyme and ISSR markers Sci. Hort. 116 421 429
Torres-Díaz, C., Ruiz, E., González, F., Fuentes, G. & Cavieres, L.A. 2007 Genetic diversity in Nothofagus alessandrii (Fagaceae), an endangered endemic tree species of the coastal Maulino Forest of central Chile Ann. Bot. (Lond.) 100 75 82
Vos, P., Hogers, R., Bleeker, M., Reijans, M., Lee, T.V.D., Hornes, M., Friters, A., Pot, J., Paleman, J., Kuiper, M. & Zabeau, M. 1995 AFLP: A new technique for DNA fingerprinting Nucleic Acids Res. 23 4407 4414
Wang, X., Wadl, P.A., Pounders, C., Trigiano, R.N., Cabrera, R.I., Scheffler, B.E., Pooler, M. & Rinehart, T.A. 2011 Evaluation of genetic diversity and pedigree within crapemyrtle cultivars using simple sequence repeat markers J. Amer. Soc. Hort. Sci. 136 116 128
Wiersema, J.H. 1997 Nelumboanaceae. Flora of North America Vol. 3 5 July 2011. <http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500796>