Lilies (Lilium sp.) have substantial ornamental, medicinal, and edible value and are the most important cut flowers worldwide (Long et al., 1999). The genus Lilium is native to the Northern Hemisphere, including Asia, Europe, and North America, and it includes ≈100 species (Anderson, 1986; McRae, 1998). These species have been classified by different authors into 5–10 sections or subgenera (Comber, 1949; De Jong, 1974; Endlicher, 1836; Mabberley, 1990). All species of Lilium show the same basic chromosome number (x = 12), similar karyotype features, and a very large genome size (Zonneveld et al., 2005). Karyotype characteristics for most Lilium species have been examined (Stewart, 1947), and two large metacentric chromosome pairs and 10 subtelocentric or telocentric pairs are always present.
China possesses the greatest Lilium diversity in the world, with ≈55 species, 36 of which are unique to China (Long et al., 1999). Some of these have been used to breed new cultivars. For example, the ‘Olympic’, ‘Lady Byng’, and ‘Queen Charlotte’, which are still grown today, were all selected from Chinese species (Long et al., 1999). As the orange flowered member of the Lilium genus, L. henryi from Hubei, China, has received considerable attention for a long time. Many cultivars, including the famous ‘Black Beauty’, were all selected from the hybrids of L. henryi with other species. ‘Enchantment’ and ‘Connecticut King’ are considered descendants part of the ancestry of L. lancifolium. L. regale is an important breeding Lilium species that has been widely grown. L. pumilum is famous for its resistance to Fusarium and Botrytis cinerea (Long et al., 1999). Two American cultivars, ‘Nepera’ and ‘City Lights’, were bred from hybrids of L. tsingtauense. Thus, Chinese Lilium plants have made an important contribution to global breeding of the genus (Long et al., 1999). To further explore, use, and protect these resources, several major projects have been dedicated to their collection and in vitro preservation (Chen et al., 2007; Zhang et al., 2004) of Lilium germplasm in three regions of China (southwest, northwest, and northeast China). Three southwestern provinces, Sichuan, Yunnan, and Tibet, form the region with the broadest population distribution of the genus Lilium, containing ≈36 species (Wang and Tang, 1980; Wu et al., 2006). Four northwestern provinces, Shanxi, Gansu, Hubei, and Henan, contain ≈14 species and cultivars (Long et al., 1999). Northeast China comprises three provinces, Heilongjiang, Jilin, and Liaoning, and some studies of Lilium germplasm have been conducted in this area (Wang and Tang, 1980).
Based on morphological and physiological characteristics, Lilium plants in China have been assigned to the sections Leucolirion, Sinomartagon, Martagon, and Lophophorum (Wang and Tang, 1980). Because of their similar morphological characteristics, especially conserved flower shapes in distantly related species, identification of Lilium species using only external morphology is difficult. For example, L. henryi, which has previously been classed into section Sinomartagon based on its morphological characteristics, matched those of L. regale and L. sulphureum quite well in a C-band pattern, and its transfer to section Leucolirion has been proposed. This is consistent with results from interspecies hybrids between L. henryi and L. regale (and related species), which are reportedly fertile (Smyth et al., 1989). However, L. henryi has always previously been assigned to section Sinomartagon.
Cytogenetic studies are useful for plant taxonomy. Cytogenetic investigations of some Lilium interspecific hybrids have received considerable attention (Lim et al., 2000, 2001a, 2001b; Noda, 1971), but cytogenetic studies are still not generally performed for Chinese Lilium species, and the reports are not always consistent. The karyotype of L. dauricum from the Mao’er Mountain region of Heilongjiang Province was 4B in a report by Yang et al. (1996), but it was reported as 3A by Rong et al. (2009). Similarly, the karyotype of L. davidii was reported as 3A in a study by Dai et al. (2006) but as 3B in a report by Xie and Wu (1993). Yu et al. (2000) analyzed the karyotypes of seven different L. sargentiae populations in China. The results showed that for all seven populations, all karyotypes belonged to Stebbin’s type 3B. The karyotypic formulas showed only a few variations: relative length, arm ratio, and secondary constitution number and distribution. Members of the same species appear to always show similar karyotypes, with minor differences reflecting their distribution.
In addition to karyotypes, FISH is another technique providing chromosomal markers that show the positions of specific genes, thereby permitting chromosomal identification. The use of FISH with 5S and 45S rDNA probes has provided molecular cytogenetic markers for the identification of somatic chromosomes in different Lilium species (Lee et al., 2014; Liu et al., 2006; Nguyen et al., 2016; Sultana et al., 2010, 2011). FISH has been used for the verification of Lilium hybrids for many years (Lee et al., 2014; Lim et al., 2001a, 2001b; Sultana et al., 2011). However, the FISH analysis of rRNA genes is still rarely used for identifying Chinese Lilium species except in a report by Liu et al. (2016). The objective of this work was to compare the karyotypes and the 45S rRNA gene locations among 15 Lilium species from China.
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