IN VITRO PROPAGATION OF PELECYPHORAASELLIFORMIS EHRENBERG AND P. STROBILIFORMIS WERDERMANN (CACTACEAE) EUGENIO PE ´ REZ-MOLPHE-BALCH* AND CARLOS ANTONIO DA ´ VILA-FIGUEROA Departamento de Quı ´mica, Universidad Auto ´noma de Aguascalientes, Edificio 60, Av. Universidad 940, 20100 Aguascalientes, Ags, Me ´xico (Received 19 April 2001;accepted 9 August 2001; editor E. E. Benson) Summar y Development of efficient in vitro propagation systems for Pelecyphora aselliformis Ehrenberg and P. strobiliformis Werdermann, two endangered Mexican species of cacti, are described. Multiple shoot formation from areoles of in vitro-germinated plantlets was achieved in two types of explants (apical and transversal) cultured in Murashige and Skoog (MS) basal media supplemented with 30 or 50gl 21 sucrose, 10 gl 21 agar and various treatments with cytokinins. Shoot production in these proliferation media was evaluated after one (60d) and three (180d) culture cycles. In P. aselliformis 13.7 shoots per explant were produced after the first cycle using apical explants in medium with 8.8 mM 6-benzylaminopurine (BA) and 30 gl 21 sucrose. In P. strobiliformis the highest proliferation rate (12.4 shoots per explant) was reached using 8.8 mM BA and 50 g l 21 sucrose with shoot transverse segments as explants. After the third proliferation cycle, 128.1 and 136.3 shoots per explant were obtained in P. aselliformis and P. strobiliformis, respectively. The shoots were elongated in MS basal medium with 3gl 21 activated charcoal and rooted in MSbasal media with indoleacetic acid (2.85 or 5.71 mM) or indolebutyric acid (2.46 or 4.90 mM). On average, rooting efficiency was 89% for P. aselliformis and 87% for P. strobiliformis. The survival frequency of the plants once transferred to soil was on average 88%. Key words: areole activation; cytokinin; micropropagation; tissue culture. Int r oduct ion Mexico has the richest diversity of cacti worldwide. Unfortu- nately, about 25% of all cacti species are listed as endangered because of habitat loss and illegal collecting fromthe wild, making this family one of the most likely to become extinct in the plant kingdom (Hubstenberger et al., 1992). The genus Pelecyphora includes twoof the more rare and endangered species of Mexican cacti. P. aselliformisis a small plant with a solitary and cespitose stem, 1–3 cm high and 2–5 cm in diameter, in habitat lying almost flat with the ground. This species is endemic to San Luis Potosı´ State and is only known from a few localities. P. strobiliformis is a plant with a solitary and occasionally cespitose stem, about 3.5cm high and 8cmin diameter, distributed in the States of San Luis Potosı´, Tamaulipas and Nuevo Leo ´n. Both species are highly prized by collectors. Some populations have been virtually eliminated and the remaining ones showdefinite signs of illegal collecting, so the species must be considered threatened (Glass, 1998). The production ofseeds and germination rate in these species are low, and their growth is extremelyslow. For these reasons it is difficult to recover endangered populations through natural procedures, and conventional propagation methods are often inadequate for those cacti that exhibit low germination rates and low or no lateral branching. Therefore, it is necessary to safeguard these species and to improve, in any possible way, the propagation techniques. During the past fewyears, plant tissue culture has emerged as a powerful tool for the effective propagation of threatened cacti (Hubstenberger et al., 1992). These techniques have the potential to produce a great number of plants in a short time and in minimal space, and their success has already been demonstrated for several endangered cacti species such as Mammillaria san-angelensis (Martı´nez-Va ´zquez and Rubluo, 1989), Aztekium ritteri (Rodrı ´guez- Garay and Rubluo, 1992), M. candida (Elias-Rocha et al., 1998), Obregonia denegrii and Coryphantha minima (Malda et al., 1999b). However, optimization of multiplication and rooting media, as well a refinement of the acclimatization transition, is necessary for each species ofinterest (Hubstenberger et al., 1992). In several studies it has also been demonstrated that in vitro development of cacti plantlets can be extremely rapid in comparison with ex vitro-cultured seedlings. This fact confers an additional advantage to this technology when applied to species of very slow growth (Ault and Blackmon, 1987; George, 1996). For example, Malda et al. (1999a) reported that in vitro-cultured plants ofCoryphantha minima grew seven-fold larger than plants cultured under similar ex vitro conditions. This was due to plant growth regulators, high relative humidityand high sugar concentration in the culture media, and an increased photosynthetic rate. In this work we are reporting systems for the in vitro propagation of Pelecyphora aselliformis and P. strobiliformis, two endangered Mexican species of cacti with extremely slow growth that are difficult to propagate by conventional methods. These systems could become valuable tools for conservation and rational use of these species. *Author to whom correspondence should be addressed: Email eperezmb@ correo.uaa.mx In Vitro Cell. Dev. Biol.—Plant 38:73–78, January–February 2002 DOI: 10.1079/IVP2001248 q 2002 Society for In Vitro Biology 1054-5476/02 $10.00+0.00 73