_??_1992 The Japan Mendel Society Cytologia 57: 485-489, 1992 Karyotype Analysis of Three Species of Sobal, L (Palmae: Coryphoideae) Guadalupe Palomino and Hermilo J. Quero Jardin Botanico , Instituto de Biologia, Universidad Nacional, Autonoma de Mexico , Apdo. Post. 70-614, Mexico, 04510, D.F. Accepted May 26, 1992 Sabal is a New World genus which grows in the Northern Hemisphere from the Caribb ean Islands, Southern United States (USA), Central America, to Venezuela. Mexico has the greatest diversity of Sabal with 7 of the 15 known species (Zona 1990).A mong the genera of palms occurring in Mexico, Sabal is one of the most economically i mportant genus, all of its species are intensively utilized by the rural population. The mature l eaves are used for thatching , the young leaves are used for make different kind of handicrafts, trunks for constructions . Sabal mexicana is also used as a source of edible "palm heart" and their fruits are used as complementary pig fodder (Caballero 1991). Four of the 7 Sabal species that occur in Mexico grow in the Yucatan Peninsula. They are, Sabal mexicana, S. mauritiiformis, S. yapa and the recently described species S. gretheriae. The three former species are clearly distinctive but S. gretheriae is closely similar to S. mexicana (Quero 1991). Palm chromosome counts have been reported for 111 genera and approximately 250 spec ies. The presence of a consecutive gametic numbers ranging from n=13 to n=18 , is called a d ysploid series. Palms of the subfamily Coryphoideae are considered to be the most primitive group with n=18 (Uhl and Druansfield 1987). Sabal is included in this subfamily and the chromosome number of 7 Sabal species have been reported n=18 , 2n=36 (Read 1965b, Uhl and Dransfield 1987, Romo et al. 1988). There are few reports of palm karyotypes. Read (1963, 1965a, 1965b, 1975), reports the chromosomes number of many palms but not the karyotype, however, this author pres ents chromosome drawings of 28 species of 22 genera. From such drawings it is possible to observe that most of the chromosomes are metacentric and few submetacentric. Essig (1970) also presents drawings of the chromosomes of 4 species of Chamaedorea, which suggest the existence of metacentrics and submetacentrics. Johnson (1979) reports the karyotypes of 2 species of Ceratolobus (2n=26) , which have metacentrics and acrocentrics. This author (1985) also reports the karyotypes of Brassiopho enix schumannii (2n=32), and Sommieria affinis (2n=34). In the latter there were found 2 pairs of telocentrics. This was the first report of telocentric chromosomes in palms. Okolo (1988) reports the karyotype of 6 species of Raphia, where he found metacentrics, submet acentrics and acrocentrics. Satellites on palms have been rarely reported. They have been found only in one acro centric pair, as in Ceratolobus concolor (Johnson 1979)and Brassiophoenixschumannii (Johnson 1985). Heteromorphic chromosomes have not been reported in any cytological study carried out in palms. The presence of chromosomes heteromorphic in both size and shape has been observed only in herbaceous plants. Changes in heteromorphic chromosomes are a result of structural genic rearrangements produced by deletions and inversions in the chromosomes of herbaceous plants (Ranganath and Krishnappa 1990, Vijayavalli and Mathew 1990, Tamura 486 Guadalupe Palomino and Hermilo J. Quero Cytologia 57 1990). This paper presents the chromosome counts and the analysis of the karyotypes on 3 of the 4 species of Sabal distributed in the Peninsula of Yucatan: Sabal yapa Wright, S. mexicana Martius and Sabal gretheriae Quero. This research is a part of the biosystematic study of the Yucatan palms, particularly, the genus Sabal. Material and methods Ripe fruits were collected from palms from different natural populations of Mexico (see Appendix 1). Seeds were scarified and germinated in sterilized Petri dishes with vermiculite. The Petri dishes were placed in a culture chamber at 30•Ž. When the seedlings grew up to few centimeters tall, they were transplanted into pots containing a mixture of sand and organic soil and were grew in the green house. Fig. 1. Somatic chromosomes of Sabal species. A, Sabal yapa 2n=36. B, Sabal mexicana 2n=36. C, Sabal gretheriae 2n=36. Arrows and numbers indicate satellites. Asterisk indi cates a pair of heteromorphic chromosomes. Scale equals 10ƒÊm. Elongated meristems of secondary roots were collected from the seedlings and were placed in a solution of 8-hydroxyquinoline (0.002 M) for 5 hr at 18•Ž , and fixed in fresh Farmer's solution (3 parts absolute alcohol: 1 part acetic acid). Later, the root tips were hydrolyzed in hydrochloric acid (1 N) for 10min at 60•Ž and transferred to Feulgen reagent (Garcia-V 1990), for 1 hr. Slides were prepared using the squash technique and the better ones were frozen with dry ice (Conger and Fairchild 1953) and mounted in Canada balsam. For the analysis of each collection, preparations for 10 plants were made , and from each, ten cells (at mitotic metaphase) were selected for study. Three of the best cells from each 1992 Karyotype Analysis of Three Species of Sabal 487 population were photographed using a Zeiss Drawing Apparatus. The chromosomes were classified according to Naranjo et al. (1986). Results A somatic chromosome number 2n=36 was found for Sabal yapa, S. mexicana and S. gretheriae. This is the first mitotic record for S. gretheriae as well as for the karyotypes of the three species. There were found satellites in the three species and a very large pair of hetero morphic chromosomes in S. gretheriae, (Figs. 1c, 2c). The data are summarized in Table 1. Photomicrographs of the somatic chromosomes and karyotypes are presented in Figs. 1 and 2 respectively. Fig. 2. Karyotypes of Sabal species. A, Sabal yapa. B, Sabal mexicana. C, Sabal gretheriae. Numbers indicate satellites and the asterisk indicate a heteromorphic chromosome pair. Scale equals 10ƒÊm. Discussion The chromosome counts of the three species studied here are in accord with previous reports in the literature for several species of Sabal (Read 1965b, Uhl and Dransfield 1987, Romo et al. 1988). Such evidence confirms that the base number of the genus Sabal is x=18. The karyotype formula (28 m+8 sm) for S. yapa and S. mexicana was similar in the metacentric and submetacentric proportion. These two species presented 4 small metacentric pairs of chromosomes with satellites. The chromosomes size and the total haploid chromatin length in their genotypes were similar in both species (Table 1). In contrast, Sabal gretheriae had remarkable differences in its karyotype (27 m+9 sm) respect to the other two species. This palm presented 9 pairs of chromosomes with satellites, 488 Guadalupe Palomino and Hermilo J. Quero Cytologia 57 8 of them in metacentric pairs and one in a submetacentric. It was also observed a big (5ƒÊm) heteromorphic chromosome pair; one metacentric and one submetacentric. This pair is almost three times bigger than the average of the other pair of chromosomes. This kind of heteromorphism, has never been found in palms before. Read (1965b) reported that the size range of Sabal chromosomes is 0.5-2.0ƒÊm. This average is similar to those found in this study for S. yapa, S. mexicana and S. gretheriae, ex cluding the heteromorphic pair observed in the latter species. The general features in the karyotype of the three species of Sabal included in this study showed that these species are related. Even though Sabal gretheriae and S. mexicana are morphologically similar, they are probably not close related species as indicated by the cy tological study as well as by anatomical evidences. It is probable that Sabal gretheriae was originated in the Caribbean region. This species could be more related to Sabal palmetto or S. maritima since they have a close anatomical similarity. Unfortunately we have not con ducted cytological studies in S. palmetto and S. maritima in order to confirm the relationship between those species at the chromosome level. Furthermore, Sabal gretheriae grows in the northeastern most point of the Yucatan Peninsula where grow other caribbean species of palms such as Roystonea regia, Thrinax radiata and Pseudophoenix sargentii . Table 1. Karyotype analysis of three species of Sabal It is possible that the presence of heteromorphic chromosomes as well as the abundance of satellites had an important role in the evolution and the establishment of Sabal gretheriae in this restricted area of the Yucatan Peninsula. Summary Chromosome counts (2n=36) and karyotypes of Sabal yapa, S. mexicana and S. gretheriae are reported. The karyotypes of S. yapa and S. mexicana were closely similar. They pre sented metacentrics and submetacentrics as well as four pairs of chromosomes with satellites. S. gretheriae showed nine pairs of chromosomes with such satellites and pair of a heteromorphic chromosomes. They were almost 3 times bigger than the average of the other chromosomes in its complement. The high number of satellites as well as the presence of a heteromorphic pair could be related to the speciation process of S. gretheriae. Appendix 1 Sabal yapa Wright. Mexico, Yucatan, Municipio Xocchel. Caballero 1888. Sabal mexicana Martius. Mexico, Yucatan, Municipio Ticul. Caballero 1887. Sabal gretheriae Quero. Mexico, Quinatna Roo, Municipio Isla Mujeres. Quero 3588. Voucher specimens were deposited at the National Herbarium (MEXU) of the Universidad Nacional Autonoma de Mexico. 1992 Karyotype Analysis of Three Species of Sabal 489 Acknowledgements This study was financed by OEA:"Estudios Biosistematicos en algunos generos de Legu minosas, Liliaceas y Palmas de Mexico": Citogenetica 88-89, PRDCyT, CONACyT and Jardin Botanico of the Instituto de Biologia of the Universidad Nacional Autonoma de Mexico . We are grateful to Javier Caballero for their comments and suggestions to the manuscript as well as for providing seeds of Sabal.