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Gene fl ow between species of different ploidy levels is important in plant evolution and breeding. A cytological study was conducted on a natural population with individuals belonging to the diploid L. purpurea Gay (2n = 10) and to the tetraploid L. coquimbensis F. Phil (2n = 18) species, as well as intermediate phenotypes of apparent hybrid origin. The genus Leucocoryne is endemic to Chile and it exhibits heterogeneity, presumably genetic, for shape, size, and color of its fl owers. The objective of the study was to determine if there is gene fl ow between species having different ploidy levels. From the karyotypic analyses of the seeds, only parental types having 2n = 10 and 2n = 18 individuals were observed. However, from the bulb analyses, 2n = 10, 2n = 18, 2n = 14, and 2n = 22 individuals were encountered. The karyotypes of the 2n = 14 and 2n = 22 individuals suggest the occurrence of natural interespecifi c hybridization between species with different ploidy levels in nature. Models which may account for the origin of these genotypes are proposed. Received for publication 26 Apr. 2004. Accepted for publication 20 May 2004. We thank Drs. R. Craig and C. Quiros for their valuable suggestions to improve the manuscript and Mr. Luis Arriagada for his assistance in collecting. This research was supported with funds from Fondo-SAG of the Servicio Agrícola y Ganadero, Chile. The genus Leucocoryne, Alliaceae family (Dahlgren et al., 1985), is a group of bulbous plants endemic to Chile. Their geographic distribution is from Northern Chile, near the city of Iquique (lat. 20°13 ́) to the southern Bio-Bio region, near the city of Concepción (lat. 36°60 ́) where only the species L. alliacea Lindley is present. The highest concentration of species and apparent center of diversity of the bulbs is between lat. 29°56 and lat. 33°01 ́ in Coquimbo and Valparaíso regions of central Chile, respectively (Zoellner, 1972). Due to the great variability of the genus, especially in its fl oral phenotype, many populations remain taxonomically unclassifi ed (Mansur, 2004). Considering this fact, cytological analyses of the chromosome number might be useful for the classifi cation of the different populations. The fi rst cytological study in Leucocoryne was conducted by Cave (1939) in L. ixioides Lindley and demonstrated a chromosomal complement of 2n = 18, composed of seven pairs of metacentric and two pairs of acrocentric chromosomes. In addition to Caveʼs work, Crosa (1988) studied nine species and observed a chromosomal complement of 2n = 10 for seven of them (L. paucifl ora Phil., L. purpurea, L. alliacea, L. angustipetala Gay., L. odorata Lindley., L. conferta Zoellner, and Leucocoryne sp.) and 2n = 18 for two species (L. violascesens Phil. and L. ixioides). Crosa (1988) established a basic bimodal complement composed of three metacentric and two acrocentric chromosomes. Araneda et al. (2004) determined the chromosome complement of 11 species/populations. They established that L. ixioides, L. coquimbensis, L. narcissoides Phil, Leucocoryne sp. Alcones, Leucocoryne sp. Talinay, and Leucocoryne sp. Combarbalá are 2n = 18; L. purpurea, Leucocoryne sp. Ñague, Leucocoryne sp. Alicahue, and Leucocoryne sp. Pichicuy are 2n = 10; and L. coquimbensis var. alba Zoellner is 2n = 14. They concluded that Leucocoryne typically has a chromosomal complement of either 2n = 10 or 2n = 18 with a similar number of species or populations at each ploidy level. The objective of this study is to analyze the karyotypes of individuals from a small population located in the Coquimbo region that exhibits a high phenotypic variability for color, shape, and size of the fl owers and in which it is possible to fi nd individuals belonging to L. coquimbensis (2n = 2x = 18) and to L. purpurea (2n = 2x = 10) as well as individuals showing intermediate phenotypes between these two species that are possibly natural interespecifi c hybrids. Materials and Methods PLANTS. The germplasm used in this study was obtained from seeds and bulbs collected in the fi eld in Oct. 2001, and only seeds in Oct. 2002, from a population of L. purpurea (2n = 10) and L. coquimbensis (2n = 18), according to the taxonomic key of Zoellner (1972), and their putative hybrids. This population is located on the Region of Coquimbo, Chile (lat. 30°22 ́29 ́ ́S, long. 71°26 ́17 ́ ́W, 91 m altitude). Bulbs from a population of L. coquimbensis var. alba from the region of Coquimbo, which were collected in 1997 and maintained in a greenhouse, were used as controls because they had previously been found to be 2n = 14 and are likely to be of interspecifi c hybrid origin (Araneda et al., 2004). Karyotypic analyses SEED. Root tips were obtained from germinated seeds collected at maturity from random individual plants in Oct. 2001 and 2002, thus the phenotypes of the fl owers were unknown. After each collection seeds were germinated following the procedure described by De la Cuadra et al. (2002). The seeds were briefl y germinated in petri dishes on absorbent paper soaked with distilled water and stored in the dark at 15 °C until the roots reached a length of 1 to 1.5 cm. From the 2001 collection, 15 seeds from each of 86 plants were used, and for the 2002 collection, 20 seeds from each of 17 plants were used. BULB. Twenty-fi ve bulbs were sampled in 2001 at the site from the putative hybrid population, most of them hybrids and a few parental types. Bulb root meristems were obtained from only NovJournal.indb 833 10/26/04 11:30:14 AM 834 J. AMER. SOC. HORT. SCI. 129(6):833–835. 2004. seven of the 25 bulbs, one L. purpurea, one L. coquimbensis, and fi ve of hybrid phenotype. In addition fi ve bulbs belonging to L. coquimbensis var. alba were also analyzed. The squash technique described by Dyer (1963) and adapted by Crosa (1988) and Araneda et al. (2004) was used. Briefl y, this consists of a fi xing solution of 3 absolute methanol : 1 acetic acid (glacial 100%) and an orcein lacto-propionic stain. Prior to fi xation, the roots were pretreated with a 0.05% colchicine aqueous solution for 20 h at room temperature. The karyotypes were based on the length of each chromosome. Chromosome measurements were made using the computer application MicroMeasure version 3.3 (Reeves and Tear, 2000). Black and white photographs of the preparations were scanned, and Adobe Photoshop 6.0 (Adobe Systems, San Jose, Calif.) software was used to assemble the karyotypes. Chromosome counts were made on at least 10 cells per individual (seed or bulb). Measurements were made on at least one and up to 36 cells per individual, then the average karyotype of individuals with the same number of chromosomes was calculated. Each chromosome was classifi ed according to the terminology of Levan et al. (1964). The bulbs used for these analyses are maintained in active growth in a greenhouse of the Leucocoryne Breeding Project, at the La Palma Experimental Station in the Facultad de Agronomía of the Pontifi cia Universidad Católica de Valparaíso, Quillota, Chile. Results and Discussion Low germination in both 2001 (18%) and 2002 (7%) seed collections was observed. Fresh seeds of Leucocoryne grown in good conditions have a germination above 90% (De la Cuadra et al., 2002). The low germination could be attributed to the interspecifi c hybrid origin of the population and less than optimal growing conditions in the fi eld. The chromosome count showed these seeds to be either 2n = 10 or 2n = 18, suggesting that only the seeds with a balanced set of chromosomes were viable. This could not be confi rmed because the hybrid bulbs have so far shown only vegetative growth in the greenhouse. Only seven of the bulbs could be analyzed. The others did not produce roots despite being stored at 20 oC for at least 4.5 months, which should have ended their dormancy (Okhawa et al., 1996). Of these bulbs, one was 2n = 10, one 2n = 18, two 2n = 14, and three 2n = 22 (Fig. 1). The 2n = 10 and 2n = 18 individuals had karyotypes similar to those of the seeds, and were typical of L. purpurea and L. coquimbensis as described by Crosa (1988) and Araneda et al. (2004). The 2n = 10 karyotypes had three longer metacentric pairs of similar lengths ranging 12–14 μm and two shorter acrocentric pairs ranging 7–10 μm, one of the st (sub-telocentric) and one of the t (telocentric) type (Fig. 1A). The 2n = 18 karyotypes had one longer metacentric pair (16–17 μm), six metacentric pairs of similar lengths (12–14 μm), and two shorter pairs (7–10 μm), the eighth pair being of the sm (sub-metacentric) type and the ninth pair of the st type (Fig. 1B). It was proposed by Crosa (1988) that the 2n = 18 individuals are tetraploids and might have originated through interespecifi c hybridization of 2n = 10 individuals followed by chromosome number reduction by centric fusion of one of the acrocentric pairs of the 2n = 10 species and genome duplication. Of the fi ve remaining bulbs, two were 2n = 14 and three were 2n = 22. Surprisingly, the karyotype of the 2n = 14 was similar to the 2n = 14 for the L. coquimbensis var. alba population described by Araneda et al. (2004). This karyotype has 10 longer metacentric chromosomes and four shorter acrocentric chromosomes, two of the st and two of the t type (Fig. 1C). Both the 2n = 14 and the 2n = 22 individuals had the longer metacentric chromosome that is only observed in the 2n = 18 species of Leucocoryne. This suggests that one of the parents of these hybrids is L. coquimbensis. We propose that the 2n = 14 is an allo-triploid hybrid originating from the cross between the diploid L. purpurea and the tetraploid L. coquimbensis (2n = 18) as shown in Fig. 2. The same could be true for L. coquimbensis var. alba in that it may be an interspecifi c hybrid rather than a botanical variety. This needs to be researched further with a larger number of samples of L. coquimbensis var. alba from various habitats. Regarding the 2n = 22 individuals whose karyotyp

Gene Flow between Parents with Different Ploidy Levels in a Natural Population of Leucocoryne Lindley