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Abstract:
Landrace crops (razas or variedades criollas in Spanish) are considered the second most important reservoir of genetic diversity for crop improvement, only after the wild crop relatives. Landrace crops are the product of centuries of selection by farmers and have locally evolved in response to both the environmental conditions of each region and different social and cultural aspects. In Mexico, the traditional landraces of pumpkins and squashes of C. pepo ssp. pepo were domesticated, cultivated and managed under the traditional cultivation system ? the milpa? starting at least 10,000 years ago, which has resulted in the development of high morphological and genetic diversity. We analyzed 8,643,037 SNPs obtained by whole genome sequencing at high coverage from 96 individuals of different landraces of C. pepo ssp. pepo representing all Mexico and Guatemala. We also included 13 individuals of the ancestor of this cultivated species, C. pepo ssp. fraterna, from the only three wild populations that we found. The traditional landrace varieties of Mexico exhibit a genetically differentiated group from their wild populations and have higher levels of genetic diversity (Cultivated ?= 0.155; Wild ?= 0.058), possibly due to the very small population sizes of the extant wild populations. We found a clear geographic differentiation among the landraces, forming four groups. We also detected 28 genes under selection. We conclude that in contrast to what is generally reported in the literature, the traditional landraces of C. pepo ssp. pepo are the most important reservoir of genetic diversity for this species.
