Genetic relationships in Opuntia Mill. genus (Cactaceae) detected by molecular marker

The Opuntia genus includes over 181 species comprising, on the basis of morphological traits, a total of 29 series [The Cactaceae (1919)]. Starting from this classification, several authors have investigated the Opuntia genus taxonomy but the large morphological variation within different species, suggests that phenotypical characteristics will not serve to produce a stable classification. In this work chloroplastic simple sequence repeat (cpSSR) and amplified fragment length polymorphism (AFLP) were used to evaluate the usefulness of molecular markers in Opuntia species characterization and to study the relationships among different species. Results show that the combination of cpSSR and AFLP markers provide a quantitative estimation of genetic relationships among several Opuntia species. Both molecular analyses reveal a genetic similarity among species of series 20 and 21 [The Cactaceae (1919)] as suggested also by morphological traits. Particular attention was focused on the genetic relationship between Opuntia ficus-indica and Opuntia megacantha: individuals from different populations of the two species were analyzed with both molecular markers. A common genetic constitution of O. ficus-indica and O. megacantha was detected. On the basis of molecular data, morphological traits and biogeographical distribution, we suggest that O. ficus-indica should be considered as a domesticated form of O. megacantha. Our results suggest the importance of a revision of Opuntia genus classification using several tools: molecular, morphological and biogeographical analysis. © 2003 Elsevier Ireland Ltd. All rights reserved.