On the origin of hops: Genetic variability, phylogenetic relationships, and ecological plasticity of Humulus (Cannabaceae).

摘要

Introgression with the domesticated hop plant (Humulus lupulus L., Cannabaceae) makes some morphological identifications difficult for wild or heirloom hop plants found on wild or fallow lands. As a result, this dissertation takes an approach using DNA barcodes to investigate the proposed polytypic model for Humulus, which is mostly based on morphology. Results from two standard DNA barcode studies with fresh and herbarium materials show the genetic variability and phylogenetic relationships. In addition, putatively wild as well as unknown hop plants were sorted into three species (H. lupulus, H. scandens, and H. yunnanensis ), while H. lupulus was further split into Western to Central Eurasia, East Asia, and the New World clades. Low resolution was found for the putative varieties of H. lupulus from East Asia and the New World. Furthermore, results from two chloroplast genome (plastome) barcode studies show the conserved relationships and unique evolutionary history within the Cannabaceae (s.s.). The phylogenomic analyses presented here suggest the Cannabaceae (s.s.) is much more ancient than previously proposed. With a mid-Cretaceous origin based on high bootstrap and posterior probability support on a polyphyletic tree with basal East Asian taxa, a Laurasian migration hypothesis is probable for Humulus. Compared to single or several DNA regions used to barcode plants, the plastome as a single DNA barcode supports the unity of the H. lupulus complex in a polytypic model. Further duplicate sampling on the phyloplastome tree is required to test the varietal relationships of H. lupulus from East Asian and the New World. More broadly, a large scale phylogenomic study on the Cannabaceae (s.l.)/Celtidaceae remains as a high priority for future research.