Study Reveals Role of Allele Dosage in Improving Sweetpotato Traits

Sweetpotatoes are an agricultural powerhouse that feeds millions globally. However, their complex genetics make it challenging for breeders to understand and improve traits like yield, disease resistance, and nutritional content. A new study reveals insights into the significance of leveraging “allele dosages” in sweetpotato breeding practices.

“Sweetpotatoes are hexaploid, meaning they have six copies of each chromosome, unlike diploid crops like tomato or rice, which have two," explained Zhangjun Fei, a professor at the Boyce Thompson Institute and one of the study's lead authors. “This genetic complexity allows for more variation and adaptability but makes selective breeding difficult. Unlike diploid crops, where single genetic changes can have noticeable effects, sweetpotatoes require a more nuanced approach.”

The researchers created a detailed map of genetic variations by analyzing 294 sweetpotato varieties. This map didn’t just look at what genes were present but also how many copies of favorable variants existed in each plant. They discovered that the differences in allele dosage significantly impact important agricultural traits such as root weight, plant architecture, and flesh color.

The study found that successful breeding programs have unknowingly targeted allele dosage over time. Modern sweetpotato varieties tend to have more copies of beneficial alleles compared to their ancestors, which explains why today's crops generally perform better.

The study focused on China, which produces over half of the world's sweetpotatoes. The researchers found that Chinese breeders have been especially successful at selecting varieties with optimal gene copies for desirable traits like larger tuberous root size and better growth in crowded conditions.

Through their research, the scientists identified an important candidate gene called IbEXPA4, which was suspected to influence tuberous root weight. They conducted a series of experiments and found that when IbEXPA4 was suppressed, the sweetpotato root grew larger, validating the gene's impact on size.

The study, recently published in Nature Plants, also revealed how sequence variations alter the expression of the Orange gene, which regulates flesh color. Understanding this mechanism could help breeders develop sweetpotatoes with enhanced nutritional content, such as increased beta-carotene.

With this new understanding, breeders can develop improved sweetpotato varieties by adjusting allele dosages at specific locations in the genome. In a world where food security is a growing concern, this research could contribute to creating high-yielding, nutritious, and resilient crop varieties.