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Umbu tree is one of the most important species in the Brazilian semi-arid region due to its ability to produce fruit in water stress environments. The objective of this work was to estimate outcrossing rates in the S. tuberosa ((t) over cap), by considering the observed and expected frequency of heterozygous in the mother and descent population (M1), respectively, and the estimate of multilocus (M2), to direct programs of conservation and genetic improvement of the species. Samples of DNA extracted from a maternal population with 96 plants established in 1991, at Petrolina, PE, as well as the DNA from one descent from each maternal plant were analyzed for the 16 polymorphic AFLP bands obtained from AAA_CTG and AAA_CTC primer combinations. In M1, it was considered the frequency of heterozygote estimated by the square root of 1 minus the AFLP fragment absence frequency, for the maternal population (observed frequency) and also for the descent population (expected frequency), whereas in the M2, the estimate was obtained by the multilocus estimate ((t) over capm). The (t) over cap estimates of M1 ranged from 1.74 to 0.50, with mean value of 1.063. Because values of (t) over cap above 1.0 are biologically inadequate, it was demonstrated that M1 was not appropriate to estimate (t) over cap. Frequencies of pollen and ovule for 15 AFLP loci were the same, suggesting good adjustment to the mixed mating model in M2. The (t) over cap rate obtained by M2 was 0.719, which was close to previous estimates with isoenzymes obtained in other umbu tree populations. Results point that umbu tree is predominantly an outcrossing species and there is the need for broad samples in order to preserve the genetic variability of this species.