Chinese Research Team Advances One-Line Hybrid Rice Breeding with High Cloning Efficiency

A research team led by Wang Kejian at the China Rice Research Institute has developed "Yixi No. 1," a one-line hybrid rice strain capable of fixing hybrid vigor through apomixis. Published in the journal Vita, the study identifies an endogenous rice gene named "HUAXU" that induces parthenogenesis when ectopically expressed in egg cells. Combined with clonal gamete strategies, the method maintains a cloning efficiency above 99% and normal grain yield across multiple varieties and generations in field trials. If commercialized, this technology could reduce reliance on costly annual seed production.

Fixing hybrid vigor through asexual seed reproduction (apomixis) has long been considered a major goal in crop breeding. Traditional two-line and three-line hybrid rice systems require re-breeding seeds every year because offspring undergo genetic segregation, driving seed costs up to ten times higher than conventional varieties. Demonstrating high cloning efficiency alongside normal yields under field conditions provides a key proof of concept for lower-cost, scalable hybrid seed reproduction.

Researchers at the China Rice Research Institute, led by Wang Kejian, have developed a "one-line" hybrid rice strain named "Yixi No. 1" that fixes hybrid vigor through apomixis, according to findings published in the journal Vita. The team achieved a stable cloning efficiency exceeding 99% while maintaining normal crop yields across different generations and field planting environments. Hybrid rice has historically contributed significantly to global food production. However, standard three-line and two-line hybrid systems suffer from genetic segregation in offspring, preventing farmers from saving seeds for subsequent planting seasons. Consequently, hybrid seeds must be produced annually by crossing male-sterile lines with restorer lines. This process is technically demanding, carries production risks, and results in seed costs that are typically more than ten times higher than those of conventional rice varieties. To address this limitation, Wang's team launched the "One-Line Hybrid Rice Exploration Plan" in 2013. The project aimed to utilize apomixis—asexual reproduction through seeds—to allow hybrid crops to generate clonal seeds that preserve genetic vigor generation after generation. In 2017, the team established its first apomictic hybrid system and produced the first clonal hybrid rice seed, though initial trials yielded a cloning efficiency of only around 5% alongside reduced seed setting rates. The team's recent progress follows the discovery of an endogenous rice gene designated "HUAXU." Researchers found that ectopic expression of the HUAXU gene in hybrid rice egg cells efficiently induces parthenogenesis, producing haploid offspring. By pairing this approach with a clonal gamete strategy, the researchers created multiple apomictic lines that consistently maintained cloning efficiencies above 99% in field trials across various hybrid varieties without sacrificing normal grain production levels. Despite the positive experimental outcomes, lead researcher Wang Kejian noted that transitioning the technology from experimental plots to broad agricultural adoption presents ongoing challenges. The research team's next phase will focus on conducting comprehensive safety tests, evaluating long-term genetic stability, and continuing to optimize the technology.