Development of single nucleotide polymorphism markers and genetic diversity in guava (Psidium guajava L.)

Societal impact statement There are many understudied fruits of great economic and productive importance for regional agricultural hubs. Guava is an American fruit species with attractive nutritional and adaptability characteristics. However, in many countries like Mexico, its cultivation is still limited to small-to-medium size plantings and home gardens and depends on poorly controlled germplasm that diminishes productivity and expansion. Our study provides valuable insight to better understand guava diversity and generate high-yielding, high-quality, and better adapted materials. Supporting the study and development of understudied crops will provide us with more resources for facing climate change adversities and for diversifying cropping systems. Summary Guava (Psidium guajava L.) is a fruit crop species native to tropical and subtropical regions of America with great productive and economic potential due to its extensive environmental adaptability, nutritional value, and medicinal properties. However, the lack of molecular resources for accelerated breeding, limited knowledge about its evolutionary and domestication history, and unfavorable policies have limited its genetic improvement and broader adoption as a commercial fruit crop. Here, we present the first diversity study in guava employing genome-wide single nucleotide polymorphisms (SNPs). Forty-eight accessions collected from Mexico and other continents were examined with more than 6000 high-quality SNP markers, which represents a marker density increase of similar to 30x compared with previous studies. Relationships between genetic groupings and geographic origins were not apparent in this diverse guava collection using principal component and structure analyses. Extensive germplasm exchange among guava-producing regions and limited varietal control at commercial plantations might have contributed to ambiguities when defining the true origin and identities of existing germplasm materials. However, an analysis of domestication syndrome traits (fruit size and sugar) by wild or improved germplasm revealed several putative genomic regions under selection. Knowledge about germplasm origins and genetic relatedness, in conjunction with reliable molecular resources and better agronomic practices, is necessary to support breeding efforts and facilitate broader adoption of orphan crops such as guava, which have increasingly important roles in light of climate change adversities and in diversifying diets and food systems.