Assessing the genetic vulnerability of Macaúba palm [Acrocomia aculeata (Jacq.) Lodd. ex Mart.] through the mating system and genetic diversity of open-pollinated progenies

At present, intelligent and sustainable agriculture presupposes a compromise between maximising crop yield and minimising its risk of genetic vulnerability. Breeding programmes should implement strategies that allow the development of superior genotypes and preserve genetic diversity, especially in perennial plants. The Macaúba palm (Acrocomia aculeata) is a species with the potential to produce oil at a level comparable to that of the oil palm, even in water-deficient areas, which motivates its commercial interest and drives an increase in demand for seedlings from natural populations for commercial plantations. Therefore, to evaluate the impact of this selection procedure on the reduction of genetic diversity and, consequently, the genetic vulnerability of commercial planting, in the present study we analysed the population mating system and the genetic diversity of Open-Pollinated Progenies (OPPs) from selected seed-trees in relation to the genetic diversity of respective native populations (NPs). To achieve this, we evaluated the mating system and genetic diversity employing 14 microsatellite markers (SSR). The mating system indices estimated for A. aculeata palm indicated that the species present a mixed mating system (${\hat{t}}_m=0.877$) with a predominance of outcrossing. However, at the population level, the outcrossing rate ranged from ${\hat{t}}_m=0.986\text{to}1.00$. The biparental inbreeding rate was considered moderate (${\hat{t}}_m-{\hat{t}}_s=0.312$), with some variation between populations (from 0.0005 to 0.275). The multilocus correlated paternity was ${\hat{r}}_p=0.389$, ranging from 0 to 0.112 at population level, indicating that a significant portion of the progeny consisted of half-sibs. The results demonstrate that there was no significant loss of genetic diversity of OPPs derived from artificial selection within NPs. In the OPPs the number of alleles (Na = 2.55) was similar to that of NP (Na = 2.56). Furthermore, the mean values of observed heterozygosity (H_O) between NP and OPPs were similar, with a mean of 0.366 and 0.356, respectively. In conclusion, the procedure adopted to produce commercial seedlings in the present study should not represent a high risk of genetic vulnerability. In addition, our results will provide a guidance to breeders regarding selection intensity in both natural and improved populations, aiming to optimise the advancement of generations, thereby maximising future genetic gains while preserving genetic diversity. However, we recommend verifying the outcrossing rate and genetic diversity at the population level, as these factors could have significant effects on the vulnerability of the species and the macaúba crop.