Winter wheat is the backbone of wheat production in China. Typically sown in autumn, it endures the cold winter, flowers in the spring of the following year, and is harvested in early summer. Unlike spring wheat, which can flower and produce grain without vernalization, winter wheat (usually winter-type varieties) requires a period of low-temperature vernalization to transition from vegetative growth to reproductive growth, enabling flowering and seed production. This requirement of vernalization makes the breeding process for winter wheat more complex and time-consuming. However, the combined application of wheat doubled haploid (DH) breeding techniques with summer and southern propagation technologies serves as a "high-speed engine" for winter wheat breeding, significantly accelerating the process.

Winter nursery propagation involves transferring breeding materials, such as rice, corn, and vegetable crops, harvested in autumn from northern regions to subtropical or tropical regions in southern China during winter for propagation and selection. This method allows 2–3 generations of propagation annually, substantially shortening the breeding cycle. Additionally, southern propagation enables more precise evaluation of disease resistance and adaptability to various humidity and light conditions, facilitating the selection of well-adapted varieties and materials.

Building on foundational research, the wheat breeding team at the Peking University Institute of Advanced Agricultural Sciences (PKU-IAAS) conducted, for the first time, direct-seeding propagation and field evaluation trials of winter wheat DH lines in Hainan. However, since Hainan's temperature conditions are insufficient to meet the vernalization requirements of winter wheat, seeds must undergo vernalization treatment prior to sowing. The research team, led by Dr. Yuehui He, published a groundbreaking study in Nature Plants, titled "A molecular mechanism for embryonic resetting of winter memory and restoration of winter annual growth habit in wheat" (https://doi.org/10.1038/s41477-023-01596-6). This study revealed the molecular mechanism underlying the "resetting of winter memory" and the restoration of winter annual growth habits in wheat, demonstrating that vernalization can be initiated in the germinating wheat embryo. Based on this discovery, the team successfully vernalized wheat “seeds” using plant growth incubators and directly sowed the treated “seeds” in the breeding nursery in Sanya, Hainan, for rapid generation propagation and comprehensive evaluation (see Figure 1). This innovative change of winter wheat breeding protocol offers new possibilities for winter wheat breeding, significantly enhancing breeding efficiency.

   

Figure 1：Vernalization Treatment of Winter Wheat DH Lines and Growth Performance After Sowing at the Sanya Breeding Nursery

Sanya, located in the sub-tropics, presents a unique climate that contrasts sharply with the temperate regions where wheat is traditionally grown. In this region, wheat traits tend to exhibit much greater variation compared to the more optimal growing conditions in northern areas. This pronounced trait segregation provides a broader scope for wheat selection, significantly increasing the chances of identifying novel materials and new varieties with superior characteristics surpassing those of their parents. These new materials can be better to adapt to variable climate challenges, thereby expanding the adaptability of wheat varieties.

In November 2024, the wheat breeding team conducted direct-seeding trials for 126 winter wheat DH lines to facilitate accelerated propagation and comprehensive evaluation under the sub-tropical conditions of southern China. Detailed assessments of the DH lines revealed a striking phenomenon: significant differences were observed among the materials in traits such as growth and development, uniformity of heading, and the number of spikelet layers (as shown in Figure 2). Notably, the range of trait segregation in Hainan far exceeded that seen in northern regions. This unique advantage enables the precise selection of novel materials and new varieties with exceptional adaptability, high stability, and superior traits beyond those of their parental lines.

Figure 2: Growth and performance of winter wheat DH lines in the Sanya breeding nursery

It is worth mentioning that Sanya's favorable climate makes the period from November to March the ideal season for wheat cultivation. During this time, winter wheat sown at different intervals experiences varying environmental factors, such as daylight duration, temperature fluctuations, and humidity changes. Notably, the winter solstice serves as a key turning point in the changes to daylight duration.

Faced with the promising results achieved in the trial fields during the initial testing, colleagues unanimously praised the wheat breeding team for yet another innovative achievement (Figure 3).

Figure 3: Breeding platform colleagues in the winter wheat DH line evaluation field

Looking ahead, we will continue to explore how winter wheat can more efficiently harness Sanya's abundant light and heat resources, uncovering its potential for germplasm enhancement under unique environmental conditions. This will provide a powerful impetus for the sustained development of wheat breeding in China.