Rare Today, Relevant Tomorrow: Lessons From an Old Barley Experiment

Key Takeaways

• CCII barley evolved over 58 generations since 1929
• Natural selection halved genetic diversity, favoring early flowering genes
• Yield doubled in field trials, yet lagged behind modern breeding
• Rare alleles resurfaced when population moved to Bozeman, showing genetic rescue
• Genebank strategies may benefit from occasional stress‑environment regeneration

Pulse Analysis

The Composite Cross II (CCII) barley experiment, launched in 1929 by Harry Harlan and Mary Martini at the University of California, Davis, is one of the longest-running evolutionary plant‑breeding studies. Starting with 28 globally sourced varieties, the researchers intercrossed them, bulked the seeds and replanted the mixed population each year. Over 58 generations, tens of thousands of seeds have been sown and harvested, creating a living archive that captures natural selection in real time. Modern genomics now allows scientists to read the genetic changes that have accumulated across a century.

Recent work published in *Science* revealed that natural selection rapidly compressed the original genetic diversity, especially at loci controlling flowering time and drought avoidance. The streamlined population showed a two‑fold yield increase, although conventional breeding achieved higher gains over the same period. Jill Marzolino’s doctoral thesis extended the analysis by relocating the CCII to Bozeman, Montana, where previously rare alleles surged in frequency. This ‘genetic rescue’ demonstrates that dormant, maladapted variants can re‑emerge under contrasting environments, providing a hidden reservoir of adaptive potential.

The findings have practical implications for crop improvement and genebank stewardship. Breeders can harness composite cross populations as a low‑cost, self‑optimizing resource to develop varieties resilient to shifting climate patterns. Meanwhile, genebank managers might deliberately expose sub‑samples to stress‑filled regeneration cycles, preserving rare alleles that could become valuable under future stresses. As climate volatility intensifies, integrating evolutionary breeding with strategic genetic rescue could accelerate the delivery of adaptable, high‑yielding crops without relying solely on intensive molecular editing.