News: Genomic Sequencing Combined With Marker-Assisted Breeding Effectively Eliminates Potential Linkage Drag Of A Target Gene: A Case Study In Tobacco.

Published 12:00 AM EST, Fri Sep 26, 2025 The comparative genomic analysis showed that 0970A inherited approximately 3.74 Mb of N. glutinosa DNA (N-fragment) from its donor, Coker 176. From screening the BC4F1 population with molecular markers, a recombinant was identified. This recombinant had a significantly reduced N-fragment (~270 kb), which minimized the linkage drag while still maintaining resistance to TMV.

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Researchers are tackling the long-standing challenge of linkage drag in plant breeding, particularly when introducing disease-resistance genes from wild species into cultivated crops. While beneficial genes, such as those conferring virus resistance, are highly desirable, they are often accompanied by linked unfavorable genes that compromise yield or quality. Identifying and minimizing these “alien” fragments is critical to ensure genetic improvement without negative trade-offs.

In tobacco, the focus has been on the N gene, which provides strong resistance against tobacco mosaic virus (TMV). First discovered in Nicotiana glutinosa, the N gene triggers a hypersensitive response that blocks viral spread. Over the decades, breeders have introgressed this gene into Nicotiana tabacum through hybridization, leading to TMV-resistant lines. However, while burley tobacco varieties benefited, flue-cured types often suffered reduced yield and quality, highlighting the cost of linkage drag.

Using advanced genome sequencing and marker-assisted breeding, researchers precisely mapped the N gene and its surrounding fragments, creating new recombinant lines with reduced linkage drag. By crossing resistant donor plants with elite but susceptible varieties, and applying molecular tools to track recombination, the team minimized unwanted genetic baggage. Their results show that genome-guided breeding can retain resistance while preserving crop performance, providing a template for reducing similar breeding constraints in other crops. Much like tobacco, cannabis breeders face challenges when introducing traits such as disease resistance, pest tolerance, or improved cannabinoid production from wild or landrace strains. Linkage drag can reduce potency, alter terpene profiles, or lower yield. The precision breeding approach demonstrated here, combining sequencing with marker assisted selection, offers cannabis breeders a roadmap to incorporate favorable traits, like resistance to powdery mildew or viral pathogens, without compromising quality. As cannabis genetics advances toward pharmaceutical grade consistency, this strategy could accelerate the development of resilient, high performance cultivars. Source: Frontiers