Research progress of maize varieties updating and upgrading, heterosis pattern, and genome analysis in China

Maize, as the crop with the largest planting area, the highest total yield, and the largest seed industry market value in China, plays a crucial role in ensuring food and germplasm security. Although China’s research and utilization of maize germplasm resources started relatively late, the unremitting efforts of several generations have never ceased in the continuous updating and upgrading of maize varieties. Chronologically, there have been seven major updates and upgrades of maize varieties since the founding of the People’s Republic of China. In the 1950s, high-yielding local landraces were extensively adopted in agricultural extension programs. Starting from the 1960s, hybrid varieties were vigorously promoted. The 1970s marked the entry into the era of single-cross hybrids, and the 1980s achieved full coverage of excellent hybrid popularization. Since the 1990s, the increasing adoption of single-cross hybrids has propelled the emergence and prosperity of China’s corn seed industry, marking the country’s entry into an era of industrialized corn production. In the early 21st century, China’s corn varieties underwent their sixth-generation renewal. During this period, a large number of elite inbred lines were developed. Currently, we have entered an era where both imported varieties and domestic varieties are flourishing, and maize yield has steadily increased. The average yield per mu has risen from 75 kg in 1960 to 439 kg in 2024. This represents a nearly sixfold increase. Following the public release of the B73 genome in 2009, the fields of maize structural genome, functional genome, heterosis mechanism, and genome breeding are developing rapidly. Dozens of high-quality maize genomes have been published. Numerous genes have been cloned through functional genome studies of key agricultural traits, including genes such as lg1 and ZmRAVL1, which optimize maize plant architecture. Notably, KRN2 gene editing has demonstrated a 10% yield enhancement. Furthermore, high-resistance gene RppM (conferring resistance to southern corn rust) and broad-spectrum disease-resistance gene ZmMM1 have been characterized, enabling the development of high-performance varieties such as the immune-enhanced “Jing 2416K”, which demonstrated a 28.7% increase in field yield. Additionally, molecular mechanisms underlying stress tolerance have been elucidated through studies of the drought-responsive gene ZmSLAC1 and cold-regulatory gene COOL1, collectively improving crop adaptability to adverse environments. The research on the heterosis mechanism has become increasingly in-depth, and more key yield-related heterosis genes have been discovered. In the field of genomic selection (GS) breeding, China has developed machine-learning-based algorithms such as CropGBM, GEFormer, and DNNGP, significantly enhancing phenotypic prediction accuracy. Studies on GS breeding have been gradually carried out, with preliminary applications achieved. In 2022, Sichuan Agricultural University utilized GS technology to predict hybrid combinations, resulting in the development of the new variety “Youdi 899”, which showed a 6% yield increase compared to major cultivated varieties. These advancements will further promote the reform of maize breeding technology, provide strong technical support for the renewal of maize varieties, and make China’s maize breeding gradually move towards the era of breeding 4.0.