No abstract

The threat of invasive plant species in island populations prompts the need to better understand their population genetics and dynamics. In the Galapagos islands, this is exemplified by the introduced guava (Psidium guajava), considered one of the greatest threats to the local biodiversity due to its effective spread in the archipelago and its ability to outcompete endemic species. To better understand its history and genetics, we analyzed individuals from three inhabited islands in the Galapagos archipelago with 11 SSR markers. Our results reveal similar genetic diversity between islands, and the populations appear to be distinct: the islands of San Cristobal and Isabela are genetically different while the population of Santa Cruz is a mixture from both. Additional evidence for genetic bottlenecks and the inference of introduction events suggests an original introduction of the species in San Cristobal, from where it was later introduced to Isabela, and finally into Santa Cruz. Alternatively, a second introduction in Isabela might have occurred. These results are contrasted with the historical record, providing a first overview of the history of P. guajava in the Galapagos islands and its current population dynamics.

Quinoa (Chenopodium quinoa Willd.) is recognized as an important crop to improve global food security. It has gained international recognition because of the nutritional value of its seeds and its broad agronomic resilience. Although several studies have attempted to characterize the genetic diversity of quinoa, none have focused on evaluating germplasm from Ecuador; the latter considered a relevant subcenter of diversity for the species. In this study, 84 accessions representing the species' cultivated range in the Ecuadorian Andes were characterized using 15 species-specific SSR markers. The extent of allelic richness (196 alleles) and genetic heterozygosity (H E = 0.71) detected for these accessions demonstrate that Ecuadorian quinoa is highly diverse. Phenetic analyzes structured Ecuadorian germplasm into 3 subgroups; each containing genotypes from all surveyed provinces. Average expected heterozygosity was high for all 3 subgroups (0.53 B H E B 0.72), and Nei-pairwise comparisons showed significant genetic divergence among them (0.31 B Nei DST-B 0.84). The lack of a clear geographic pattern in the genetic structure of Ecuadorian quinoa led us to believe that the 3 reported subgroups constitute independent genetic lineages representing ancestral landrace populations which have been disseminated throughout Ecuador via informal seed networks. Nevertheless, a Wilcoxon test showed that at least one subgroup had been subject to intensive inbreeding and selection; and possibly corresponds to the local commercial variety INIAP-Tunkahuan. Our results show that ancestral quinoa diversity in Ecuador has prevailed despite the introduction of commercial varieties, and should be preserved for future use in breeding programs.