Hybrid Vigor: Breeding Better-quality Plants, Animals

China is one of the earliest countries in the world to systematically make use of hybrid vigor (heterosis). From the pre-Qin period to the Ming and Qing dynasties, a comprehensive practical framework was developed for animals, silkworm farming, crops and horticulture using hybrid vigor, where better quality animals and plants result from crossbreeding.

During the Western Zhou and Spring and Autumn period, the Yi Zhou Shu and Chu Ci document the hybridization of horses and donkeys to produce mules. Northern nomadic peoples pioneered interspecific hybridization techniques, and mules were considered "extraordinary animals." During the Han dynasty, mules spread to the Central Plains through contact with various ethnic groups and became important draft animals. However, hybridization techniques were still in the exploratory stage. By the Wei, Jin and Northern and Southern dynasties, this technology had gradually matured.

During the Ming dynasty, breakthroughs were achieved in silkworm hybridization. In Song Yingxing's Tiangong Kaiwu (The Exploitation of the Works of Nature), hybridization between silkworm varieties is recorded, with the achievement of "superior hybrids" clearly identified: A yellow-cocooned female and a white-cocooned male produced offspring with brown cocoons that possessed traits of both parents. This is the world's earliest written record of utilizing hybrid vigor in silkworms, predating the West by several centuries.

During the Qing dynasty, refined breeding techniques were developed. In goldfish hybridization, the Jinyu Tupu (Illustrated Treatise on Goldfish) recommended selecting superior breeds and matching traits for hybridization, resulting in varieties such as variegated and dragon-eye — a prime example of hybrid vigor in ornamental animals.

In rice breeding, naturally mutated rice plants were discovered, and after years of selection, varieties of imperial rice were developed that exhibited early maturity and high yield. Successful trials were conducted in the northern regions such as Chengde and Beijing, overcoming planting boundaries.

The characteristics of ancient Chinese utilization of hybrid vigor can be summarized in four points: First, animal-led hybridization, represented by mules and dzo (cow and yak hybrid). This was the earliest and most successful example of distant hybridization in the world. Second, a milestone in silkworm breeding. Inter-variety hybridization was achieved in the Ming dynasty, clearly demonstrating the concept of "generating superior varieties," making China a pioneer in insect hybrid vigor.

Third, the practice-driven approach, primarily based on production experience rather than modern genetic theory, yet the techniques were precise and the results significant. Fourth, its applications were wide-reaching, covering draft power, food, textiles and ornamental uses, and supporting the development of ancient agriculture and handicrafts.

The use of hybrid vigor in ancient China predates that in the West by around 1,000 years, representing a significant innovation in the history of world agricultural science and technology, and providing the practical basis for modern hybrid breeding, including hybrid rice, corn and livestock.

Source: Science and Technology Daily