Royero N. 1,5, Mejía-Jiménez A. 2, Sánchez I. 3, Saavedra R. 4, Gallego G. 2, Duque MC. 2, Tohme J. 2 1 Corporación BIOTEC, CIAT, 2 Centro Internacional de Agricultura Tropical - CIAT A.A. 6713, Cali, Colombia ; 3 Corporación Colombiana de Investigaciones Agropecuarias – Corpoica, CIAT, Colombia; 4 C.I. Corpoica, Palmira, Colombia; 5 Universidad Nacional de Colombia, Palmira Soursop like most Annona and Rollinia species has a neo-tropical origin. This is why in countries of northern South America a great genetic variability of soursop may be found. However, its genetic resources have not been systematically studied, neither is the genetic variability known, variability which is useful for selecting high yields or pest resistant cultivars. Colombian Corpoica guards the only Annonaceae live germplasm bank of Andean countries that could be used to breed soursop planting material. Some agro-morphological characteristics of this bank have been evaluated recently (Mejía et al., 2002). Molecular markers are a huge universe of genetic information that are not modified by the environment. They could be use to assess the divergence between organism. Our objective in this study was to characterize the genetic variability of soursop and related Annonaceae species accessions of the Corpoica germplasm bank using AFLP markers. Annonaceae is a pantropical family of about 130 genera and 2000 species. Its plants are mainly trees with simple, alternate leaves, bisexual flowers with numerous stamens and carpels and monocarpus fruits. They are useful as ornamental and medicinal plants. They are source of edible fruits as well as cosmetic extracts too. Most of the horticulturally important species belong to the tropical genera Annona and Rollinia and have syncarpous fruits (Fig. 1). Mejía-Jiménez, A et al., 2002, Final report of the project “Molecular and agromorphological characterization of the genetic variability of native soursop (Annona muricata L.) and related Annonaceae species”. Vos, P et al AFLP: a new technique for DNA fingerprinting. Nucleic Acids Res 23: 4407 – Dendrogram of 37 soursop accessions revealed by UPGMA analysis based on AFLP fingerprintings with two primer pairs. 2 Outgroups (see Fig 3) Plant Materials:  39 accessions of Annonaceae species (global analysis); and 37 soursop accessions (specific analysis) sampled from several agroecological zones of Colombia AFLP methodology:  DNA extraction (Dellaporta et al., 1983)  AFLP fingerprinting with two selective primer pairs (Vos et al., 1995)  AFLP fragment separation on silver stained 6 % polyacrylamide gels Data Analysis:  AFLP bands scored as present (1) or absent (0) in each accession  Estimate of genetic similarity based on Nei-Li (1979) coefficient  Cluster analysis  Estimate of genetic diversity based on Nei heterozygosity parameters Soursop is the most important Annona species for industrial purposes. It is consumed fresh or processed as juice, ice cream, yogurt or desserts. It has a characteristic sour flavor and is very tasty. Soursop is a fruit crop in Colombia, Ecuador, Venezuela, Costa Rica and Brazil, offering high incomes to farmers. Nevertheless it is cultivated on a small area, producing low yields. Primer combinations E-AGC/M-CTC and E-AGC/M-CAA detected high polymorphism in Annonaceae accessions. Primer combinations E-ACT/M-CAA and E-AGC/M-CTC revealed a polymorphism of 36% in the soursop accessions (Table 1). In either of the analysis, polymorphism was higher than the one found previously by allozymic markers. Between accessions no equal AFLP pattern was found, then there were not duplicates within the germplasm bank (Figure 2). Figure 2. Silver stained polyacrylamide gel displaying AFLP fingerprints detected in 37 soursop accessions using primer combination E-ACT/M-CAA. (O) outgroups; (WM) 10 bp and 25 bp ladders A Gene diversity for soursop accessions was low (0.09) and no organized groups were found according to their geographical source (Table 1). This homogeneity could arise because soursop accessions were sampled from cultivated zones and there was an interchange of seeds between indigenous people and farmers since prehispanic times. Another reason could be that the samples evaluated were not representative for all the extant variability. The Colombian collection of soursop showed low genetic variability. To collect and characterize new soursop germplasm from its whole distribution area is recommended to assess the extant diversity and evaluate the representativeness of the collection analysed. Also it would be necessary to study the variability of new soursop related species. That way, new useful characters such as high yield and disease resistance would be available for soursop breeding. Table 1. This work is financially supported by COLCIENCIAS-BID, Ginés-Mera grants of CBN and the participating institutions Corporación BIOTEC, CIAT and Corpoica. We thank Dr. J Cabra and professor JE Muñoz for recommendations. Soursop accessions (G5) showed low similarity with the other Annonaceae species (≤ 0.22). This may explain why no fertile hybrids have been produced up to now between soursop and any of the species here evaluated. Conventional breeding through interspecific hybridization with these species may be limited. A. glabra Pond apple Rollinia sp. Biriba A. montana Mountain soursop A. muricata Soursop A. reticulata Custard apple A. cherimola cherimoya A. squamosa Sweetsop Cherimoya (Annona cherimola) and Atemoya (A. squamosa x A. cherimola) are the most consumed around the world. There are other species of local importance that could reach international markets once their delicious taste and nutritive properties are promoted (Fig.1). In the global analysis nine genetic groups were detected (G1-G9), each one corresponding to at least one Annonaceae species. Low similarity (≤ 0.30) was revealed between them. Sweetsop (G9) and cherimoya (G8) accessions were the closest groups, they unified at 0.53 of similarity and included their atemoya hybrids (Figure 3). Figure 3. Figure 1 Horticulturally important Annonaceae: A) Atemoya; B) Cherimoya (“Chirimoya”); C) “Anón amazónico” (Rollinia mucosa); D) Sweetsop (“Anona Blanca” – Annona squamosa); E), F) Bullock´s heart (“Anona colorada”– A. reticulata); G) soursop “Guanábana”). Variability parameters of the Annonaceae and soursop accessions based on AFLP fingerprintings with two primers combinations. Dendrogram of 39 Annonaceae accessions revealed by UPGMA analysis based on AFLP fingerprintings with two primer pairs. Nine groups were detected (G1-G9). G2 – species unidentified and G6 – maybe A. purpurea are not illustrated. 2 Cadmia (Cananga odorata) was an outgroup. Figure 4.