A research team says it has found a way to cross bak choi – also called bok choy – with other vegetables such as mustard greens. The new technology could lead to cross-species vegetable breeding, they said in a paper published in the peer-reviewed journal Nature on Wednesday. When a bee collects nectar in the wild, its body is covered with pollen that comes from rapeseeds, timothy grasses or various flowers. But when it stops at a bak choi flower, only the pollen from another bak choi can bind with the flower and produce seeds. The question of how plants choose a mate has puzzled scientists for a long time. The international team, led by professors Duan Qiaohong of Shandong Agricultural University in China and Alice Cheung at the University of Massachusetts in the United States, revealed the molecular mechanisms of the reproductive barrier in Brassicaceae, a big plant family that includes bak choi. Based on that, they developed a breeding technology that breaks the barrier, opening up a new approach to breeding between distant species. Brassicaceae include many important vegetables and oil crops, including cabbage and mustard greens. “In nature, the stigma of an open flower is exposed to pollen from its own species, closely and distantly related interspecies, therefore must respond accordingly,” Duan said in the paper. In a press release about the research, Duan said: “On one hand, the stigma rejects self-pollen and accepts cross-compatible pollen, preventing the loss of offspring diversity due to ‘inbreeding’. On the other hand, it rejects pollen from distant species to maintain genetic integrity.” The same vegetable grown on two continents may become reproductively isolated because of a lack of continuous gene exchange for a long period. Yet so far, little is known about the molecular mechanisms regulating these compatibility systems and their interconnections in the Brassicaceae. ‘Hold the rice bowl steady’: China’s Xi Jinping repeats call for food security Through experiments, the team discovered that the stigma controls the process with a chemical regulator, reactive oxygen species (ROS). When self-pollen is detected by the stigma’s receptor, it activates ROS production and inhibits the growth of pollen, preventing self-pollination. Based on this mechanism, the team developed breeding technologies that promote interspecies breeding. By removing ROS from stigma in various ways, such as deleting the receptor gene, cutting bio-production of ROS or spraying sodium salicylate chemicals to inhibit ROS, their technology makes interspecies breeding possible. In agricultural production, artificial selection speeds up the natural breeding process. Some crops often lose good traits such as disease resistance during the long-term breeding process for yield and quality. Wild species are often resistant to diseases and insects due to their long-term survival and evolution in the wild. Traditionally, the reproductive barrier prevents breeding between distant species. If the barrier could be broken, genes from wild species could be introduced into cultivated species and bring high-quality traits. Through interspecies breeding, bak choi cultivated in China could acquire disease resistance from field mustard grown in Europe, which could ultimately lead to distant breeding in Brassicaceae crops. “We have successfully obtained interspecific and intergeneric hybrid embryos of bak choi through our breeding technology. It breaks the barrier in the Brassicaceae and builds a solid foundation for us to create new germplasm,” Yang Lin, first author of the paper, said in a press release from Shandong Agricultural University. Eat your greens for stronger arms and legs, scientists say According to an anonymous reviewer from the journal, this work makes important progress in understanding the fertilisation mechanism of Brassicaceae crops. And it will promote much discussion and further research in related fields “This study also provides new ideas for the utilisation of wild resources for other crops,” said Huang Sanwen, president of the Chinese Academy of Tropical Agricultural Sciences.