An international team has successfully propagated a commercial hybrid rice variety as a clone from seed with 95 percent efficiency. According to the University of California, Davis, this could reduce the cost of hybrid rice seeds, allowing low-income farmers around the world to access high-yielding, disease-resistant rice options.
Half of the world’s population depends on rice as a staple food, but rice hybridization is expensive and only increases yields by about 10 percent.
According to Gurdev Khush, an emeritus adjunct professor in the Department of Plant Science at the University of California, Davis, this indicates that the benefits of rice hybrids have not yet reached a significant portion of the world’s farmers.
Husch was instrumental in the development of new high-yielding rice varieties, working at the International Rice Research Institute from 1967 until his retirement from the University of California, Davis in 2002. For this achievement, he was awarded the World Food Prize in 1996.
Reproduction of hybrids as clones that will remain unchanged from generation to generation without further breeding may be one approach to this problem. A phenomenon known as apomixis allows many wild plants to create seeds that are exact copies of themselves.
“If you have a hybrid, if you can induce apomixis, you can plant it every year,” Hush said.
In the Department of Plant Biology and Plant Sciences at the University of California, Davis, a group led by Professor Venkatesan Sundaresan and Associate Professor Imtiyaz Khanday performed apomixis in rice plants four years ago, with approximately 30 percent of the seeds being clones.
Using a commercial hybrid rice variety, Sundaresan, Khanday and colleagues from France, Germany and Ghana demonstrated that the process can be sustained for at least three generations and achieve a clonal efficiency of 95 percent.
“Apomixis in crop plants has been the subject of worldwide research for more than 30 years because it has the potential to make hybrid seed production accessible to all,” Sundaresan said. “The resulting yield increases can help meet the global needs of a growing population without increasing land, water and fertilizer use to unsustainable levels.”
According to Sundaresan, the results can be applied to other food crops. In particular, rice serves as a genetic template for other cereals.
The introduction of asexual reproduction through seeds (apomixis) in crop species could revolutionize agriculture by allowing clonal propagation of F1 hybrids with increased yield and stability. It has been shown that synthetic apomixis can be engineered in inbred rice by inactivating three genes (MiMe), which leads to the conversion of meiosis to mitosis in a line that ectopically expresses the parthenogenetic trigger BABYBOOM1 (BBM1) in eggs. However, only 10-30% of the seeds are clonal. Here, we show that synthetic apomixis can be achieved in a F1 rice hybrid by inducing MiMe mutations and BBM1 expression in ovules in a single step. We create hybrid plants that produce more than 95% clonal seeds in several generations. The clonal apomictic plants retain the F1 hybrid phenotype for generations to come.