Genomic diversity in two wild gourds from Mexico (Cucurbita okeechobeensis ssp. martinezii and C. lundelliana)

Cita: Castellanos-Morales, G., Aguirre-Dugua, X., Scheinvar, E., Sánchez-de la Vega, G., Gasca-Pineda, J., Aguirre-Planter, E., et. al.2021. Genomic diversity in two wild gourds from Mexico (Cucurbita okeechobeensis ssp. martinezii and C. lundelliana). II Congreso Latinoamericano de Genética para la Conservación. Sao Paulo, Brasil.
II Congreso Latinoamericano de Genética para la Conservación

Periodo de realización: 1900/01/01 al 2021/09/14

Tipo: Ponencia

Lugar(es) de estudio: São Paulo, Estado de São Paulo, Brasil
Resumen: "Crop wild relatives (CWRs) represent strategic reservoirs of genetic diversity that result in evolutionary potential. Pumpkins, squash and gourds (Cucurbita spp.) constitute an American genus of 15 taxa, and Mexico is the centre of diversity for this genus. Cucurbita’s CWRs represent important plant genetic resources for the improvement of squashes and pumpkins, but little is known about the evolutionary history of each taxon. Moreover, many of these taxa have restricted distribution and their population trends and levels of genetic diversity are unknown. Cucurbita okeechobeensis and C. lundelliana are sister species and are the closest wild relatives (excluding crops’ direct ancestors of crops) of Mesoamerican cultivated cucurbits. They are capable of hybridizing with domesticated species and have been used to transfer disease resistance to domesticated pumpkins. Germplasm collection and genetic characterization of these wild Cucurbita are urgent, as their distribution is expected to decrease as a result from global climate change. These taxa have restricted distributions and are allopatric, and environmental analyses showed certain degree of environmental differentiation between them. The aim of this study is to characterize the levels of genetic diversity and genetic structure among these species. Between 2017 and 2019 we sampled 9 localities of C. okeechobeensis ssp. martinezii (n = 32 individuals) and 25 localities for C. lundelliana (n=76). We performed genotyping-by-sequencing and used the genome of C. argyrosperma ssp. sororia to conduct SNP calling. We obtained a final dataset of 1638 SNPs, that were used to estimate basic measures of genetic diversity and to analyze genetic structure. Genetic diversity was higher in C. lundelliana (HE = 0.225) than in C. okeechobeensis ssp. martinezii (HE = 0.183), as was previously reported using isozymes. Genetic variation was higher than that reported with GBS for other wild Cucurbita. Each taxon constitutes a different genetic lineage with signals of a hybrid zone in Tabasco, Mexico. Within C. lundelliana we could observe two genetic groups: west Yucatan Peninsula and east Yucatan Peninsula. Overall, our results show that both species include a fair amount of genetic variation and genetic structure that should be considered in management programs. Our results highlight that each genetic cluster should be considered a management units for conservation. Future analyses will focus on identifying adaptive genetic variation and on the role of hybridization in the evolutionary history of these taxa, and in their response to future climate conditions."

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