Tomato spotted wilt virus (TSWV) is one of the most economically significant viral pathogens in row crops, causing an estimated $1 billion in annual agricultural losses globally. TSWV affects peanuts and more than 200 other host species. Despite advances in tolerant varieties and agronomic management, genetic resistance remains a priority for breeding programs.
In the mid-1990s, a peanut line showing strong resistance to TSWV was identified. Although not agronomically elite, it carried a highly valuable resistance phenotype. Over the next two decades, multiple mapping populations were developed and evaluated in attempts to localize the underlying resistance locus, but conventional marker-based approaches and reference-based analyses failed to identify the causal variant.
The phenotype was reproducible in the field, but its genetic basis was unidentifiable.
Traditional trait-mapping approaches and single-reference analyses could not clearly resolve the signal to identify the responsible genetic variant. The phenotype existed, but it was frustratingly out of reach for decades.
That changed with HudsonAlpha Institute for Biotechnology’s Khufu platform, and the power of pangenomes.
A Known Trait Without a Known Cause
By the time a team led by HudsonAlpha Faculty Investigator Josh Clevenger, PhD, started working on the problem, breeders had already spent nearly 20 years trying to identify the causal locus. Through collaborative efforts and funding from University of Georgia, USDA-ARS, and USDA NIFA, Dr. Clevenger’s team was able to crack the case and solve a decades-long mystery.
In virus resistance, structural variation and gene copy number can play important roles, but many standard genotyping approaches focus primarily on SNP markers and reduced-representation genome sequencing. If the gene related to disease resistance were structural or dependent on duplicated gene cassettes, it could easily be missed.
To solve a problem that had resisted conventional approaches for two decades, the team needed more than SNPs. They needed deeper, more precise variant insight.
The Khufu Approach: Precision Through Pangenomes
HudsonAlpha’s Khufu was designed to maximize the power of short-read, low-pass whole genome sequencing. Paired with KhufuPAN, a Khufu add-on package for generating custom pangenome graphs, Khufu enables mapping within a broader genomic context that reflects true population diversity, instead of aligning short reads to a single reference genome, which can introduce reference bias and obscure structural differences.
Using scaled sequencing across thousands of individuals in a segregating population, the team applied this approach to the TSWV resistance question. The result was transformative.
Rather than identifying a single SNP, the pangenome graph revealed a duplicated gene cassette comprising four copies of a glutamate receptor gene. This copy number variation turned out to be the key. Individuals carrying four copies exhibited strong resistance. Those with fewer copies showed moderate resistance. Plants with zero copies were fully susceptible.
Traditional tools were not designed to detect or interpret this kind of complex, copy-number-dependent variant. Khufu’s ability to call and type structural variants within a pangenome framework made the difference.
From Discovery to Usable Insight
Identifying the variant was only part of the solution. For breeders, insight must translate into action.
Because Khufu enables precise identification of structural variants across large populations, the team could immediately incorporate this knowledge into selection workflows. Rather than relying solely on observing a phenotype under variable field pressure, breeders can now directly select for the optimal copy number configuration.
The team hypothesized that this locus might carry broader viral resistance beyond TSWV. The possibility of extending protection to additional geographies underscores the real-world impact of precise genomic insight.
Why It Matters
The TSWV case is more than a technical success story. It represents a shift in how unsolved breeding challenges can be approached.
For 20 years, the resistance locus remained just out of reach. With Khufu’s integration of low-pass sequencing and pangenome-guided variant detection, the team moved beyond approximate marker associations to precise, usable variant insight.
When breeders can see the full spectrum of genomic variation, including structural and copy number differences, they can solve problems that were once unsolvable.
Khufu did not just add more data. It delivered clarity and transformed a long-standing mystery into an actionable solution, increasing disease resistance and enabling stronger breeding decisions for farmers and breeders that had lost billions over the decades.
Ready to uncover the variants your current workflow might be missing?
If you’re working on complex traits that are still unresolved after using traditional reference-based or SNP-driven approaches, Khufu and KhufuPAN may provide the clarity you need. Schedule a free consultation with our team to discuss your species, population structure, and breeding goals, and explore how pangenome-guided variant discovery can accelerate your program.
HudsonAlpha Institute for Biotechnology: Advancing science, improving lives through cutting-edge genomics.
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