Most Tibetan weedy barleys originated via recombination between Btr1 and Btr2 in domesticated barley

Tibetan weedy barleys reside at the edges of qingke(hulless barley)fields in Tibet(Xizang).The spikes of these weedy barleys contain or lack a brittle rachis,with either two-or six-rowed spikes and either hulled or hulless grains at maturity.Although the brittle rachis trait of Tibetan weedy barleys is similar to that of wild barley(Hordeum vulgare ssp.spontaneum Thell.),these plants share genetic similarity with domesticated barley.The origin of Tibetan weedy barleys continues to be debated.Here,we show that most Tibetan weedy barleys originated from cross-pollinated hybridization of domesticated barleys,followed by hybrid self-pollination and recombination between Non-brittle rachis 1(btr1)and 2(btr2).We discovered the specific genetic ancestry of these weedy barleys in South Asian accessions.Tibetan weedy barleys exhibit lower genetic diversity than wild and Chinese landraces/cultivars and share a close relationship with qingke,genetically differing from typical eastern and western barley populations.We classified Tibetan weedy barleys into two groups,brittle rachis(BR)and non-brittle rachis(NBR);these traits align with the haplotypes of the btr1 and btr2 genes.Whereas wild barleys carry haplotype combinations of Btr1 and Btr2,each showing lower proportions in a population,the recombinant haplotype BTR2H8+BTR1H24 is predominant in the BR group.Haplotype block analysis based on whole-genome sequencing revealed two recombination breakpoints,which are present in 80.6%and 16.8%of BR acces-sions according to marker-assisted analysis.Hybridization events between wild and domesticated barley were rarely detected.Thesefindings support the notion that Tibetan weedy barleys originated via recom-bination between Btr1 and Btr2 in domesticated barley.

Evolutionary Genomics of Weedy Rice in the USA

Red rice Is an Interfertlle, weedy form of cultivated rice （Oryza sativa L.） that competes aggressively with the crop In the southern US, reducing yields and contaminating harvests. No wild Oryza species occur In North America and the weed has been proposed to have evolved through multiple mechanisms, Including ＂de-domestication＂ of US crop cultlvars, accidental introduction of Asian weeds, and hybridization between US crops and Asian wild/weedy Oryza strains. The phenotype of US red rice ranges from ＂crop mimics＂, which share some domestication traits with the crop, to strains closely resembling Asian wild Oryza species. Assessments of genetic diversity have Indicated that many weed strains are closely related to Asian taxa （Including indica and aus rice varieties, which have never been cultivated In the US, and the Asian crop progenitor O. ruflpogon）, whereas others show genetic similarity to the tropical Japonica varieties cultivated In the southern US. Herein, we review what Is known about the evolutionary origins and genetic diversity of US red rice and describe an ongoing research project to further characterize the evolutionary genomlcs of this aggressive weed.