Molecular Plant Breeding 2024, Vol.15, No.3, 112-131 http://genbreedpublisher.com/index.php/mpb 113 2 Origin and Early Evolution of Cucurbitaceae The origin and early evolution of Cucurbitaceae are characterized by an Asian origin, multiple long-distance dispersal events, and significant genomic changes, including polyploidization. These factors have collectively shaped the wide diversity and global distribution of the family. 2.1 Geological and fossil evidence of early Cucurbitaceae The Cucurbitaceae family, with its significant economic and biological importance, has a deep evolutionary history that can be traced back to the Late Cretaceous period. Geological and fossil records, combined with phylogenetic studies, suggest that the family originated in mainland Southeast Asia during this era. The earliest divergences within the family date back to 70–80 million years ago, indicating an ancient lineage that has since diversified into a wide array of genera and species (Renner and Schaefer, 2016). Historical records, including archaeobotanical finds, iconography, and literature, have provided evidence of the use of cucurbits by humans. For instance, Cucurbita spp. were first cultivated in the Americas over 10 000 years ago, with indigenous American peoples developing various cultivar-groups of pumpkins and squash by 1492 CE. Watermelons have a history of cultivation in northeastern Africa dating back at least 4 000 years, initially valued for their water content. Melons and cucumbers, native to Asia, were likely first cultivated for their young fruits as vegetables. Melons spread to eastern Africa early on, while cucumbers, a more recent domesticate, spread westwards to Europe in early medieval times (Paris, 2016). 2.2 Theories on the geographical origin of the family Theories on the geographical origin of Cucurbitaceae have been shaped by extensive phylogenetic research. A comprehensive multigene phylogeny, which included a wide sampling of species from herbarium collections, points to an Asian origin of the family. This is supported by the fact that two of the oldest clades within the family are now almost exclusively found in Asia. The family’s spread to other continents, such as Africa, the Americas, and Australia, is attributed to numerous long-distance dispersal events, which have been a significant factor in the family’s global distribution (Schaefer et al., 2009). 2.3 Domestication history and phenotypic evolution of Cucurbitaceae crops A comprehensive phylogenetic analysis has provided insights into the domestication of these crops, suggesting that an annual life cycle may have been a contributing factor. The domestication of these species is believed to have begun around 11 000 years ago in the New World and Asia, with some evidence of more recent domestication in Africa. Notably, certain crops like melon were domesticated multiple times from different populations in Asia and Africa (Figure 1) (Chomicki et al, 2019). The study by Chomicki et al. (2019) offers a valuable perspective on the domestication syndrome within the Cucurbitaceae family, examining how selective breeding has altered key phenotypic traits such as size, shape, and taste of fruits from their wild ancestors. Understanding these transformations is crucial for appreciating the impact of human agriculture on plant biodiversity and for guiding future breeding strategies aimed at improving crop yield, resistance, and nutritional content. The use of visual comparisons between wild and domesticated forms provides a clear and immediate understanding of the extent of changes induced by selective breeding. Such insights are essential for geneticists and breeders who aim to harness the genetic potential of wild progenitors to introduce desired traits into modern cultivars, thereby enhancing genetic diversity and crop resilience. The domestication of Cucurbitaceae crops has been characterized by the selection of non-bitter and palatable fruit, a trait that was favored early in the process. Genomic studies have shed light on how the loss of bitterness was achieved through convergent evolution. Additionally, the genetic pathways involved in the accumulation of lycopene, which contributes to the red or orange color of the pulp, as well as the determination of fruit size and shape, are beginning to be elucidated (Chomicki et al., 2019).
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