AOBPreview originally published online on August 25, 2004
Annals of Botany 2004 94(4):527-534; doi:10.1093/aob/mch183
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Annals of Botany 94/4, © Annals of Botany Company 2004; all rights reserved
Genetic Relationships among Hylocereus and Selenicereus Vine Cacti (Cactaceae): Evidence from Hybridization and Cytological Studies
1 Department of Life Sciences, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel, 2 Levi Eshkol School of Agriculture, The Hebrew University of Jerusalem, POB 12, Rehovot 76100, Israel and 3 The Institutes for Applied Research, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel
* For correspondence. E-mail mizrahi{at}bgu.ac.il
Received: 8 December 2003 Returned for revision: 20 February 2004 Accepted: 5 July 2004 Published electronically: 25 August 2004
• Background and Aims Hylocereus and Selenicereus are native to tropical and sub-tropical America. Based on its taxonomic status and crossability relations it was postulated that H. megalanthus (syn. S. megalanthus) is an allotetraploid (2n = 4x = 44) derived from natural hybridization between two closely related diploid taxa. The present work aimed at elucidating the genetic relationships between species of the two genera.
• Methods Crosses were performed and the putative hybrids were analysed by chromosome counts and morphological traits. The ploidy level of hybrids was confirmed by fluorescent in situ hybridization (FISH) of rDNA sites. Genomic in situ hybridization (GISH) was used in an attempt to identify the putative diploid genome donors of H. megalanthus and an artificial interploid hybrid.
• Key Results Reciprocal crosses among four diploid Hylocereus species (H. costaricensis, H. monacanthus (syn. H. polyrhizus), H. undatus and Hylocereus sp.) yielded viable diploid hybrids, with regular chromosome pairing. Reciprocal crosses between these Hylocereus spp. and H. megalanthus yielded viable triploid, pentaploid, hexaploid and aneuploid hybrids. Morphological and phenological traits confirm the hybrid origin. In situ detection of rDNA sites was in accord with the ploidy status of the species and hybrid studied. GISH results indicated that overall sequence composition of H. megalanthus is similar to that of H. ocamponis and S. grandiflorus. High sequence similarity was also found between the parental genomes of H. monacanthus and H. megalanthus in one triploid hybrid.
• Conclusions The ease of obtaining partially fertile F1 hybrids and the relative sequence similarity (in GISH study) suggest close genetic relationships among the taxa analysed.
Key words: Cactaceae, fluorescent in situ hybridization (FISH), genetic relationships, genomic in situ hybridization (GISH), Hylocereus, pitaya, polyploidy, Selenicereus, vine cacti
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