Rice breeding breakthrough can be a solution to food shortage by feeding billions
An international team has successfully propagated a commercial hybrid rice strain as a clone from seeds with 95 percent efficiency. This could reduce the cost of hybrid rice seed, allowing low-income farmers around the world to access high-yielding, disease-resistant rice variants, according to the University of California, Davis.
Half of the world's population depends on rice as a staple food, yet hybridizing rice is rather expensive and only improves yields by approximately 10 percent.
According to Gurdev Khush, adjunct professor emeritus in the Department of Plant Sciences at UC Davis, this indicates that the advantages of rice hybrids have not yet reached a significant portion of the world's farmers.
Khush directed efforts to develop new rice high-yield varieties while working at the International Rice Research Institute from 1967 until his retirement to UC Davis in 2002. For this accomplishment, he was awarded the World Food Prize in 1996.
The reproduction of hybrids as clones, which would remain unaltered from generation to generation without further breeding, could be one approach to this problem. A phenomenon known as apomixis allows many wild plants to create seeds that are exact replicas of themselves.
"Once you have the hybrid, if you can induce apomixis, then you can plant it every year," Khush said.
Cloned Hybrid Seeds
At the UC Davis Departments of Plant Biology and Plant Sciences, a group under the direction of Professor Venkatesan Sundaresan and Assistant Professor Imtiyaz Khanday accomplished apomixis in rice plants four years ago, with roughly 30 percent of seeds being clones.
Using a commercial hybrid rice strain, Sundaresan, Khanday, and associates from France, Germany, and Ghana have now demonstrated that the process could be sustained for at least three generations and reached a clonal efficiency of 95 percent.
"Apomixis in crop plants has been the target of worldwide research for over 30 years because it can make hybrid seed production can become accessible to everyone," Sundaresan said. "The resulting increase in yields can help meet the global needs of an increasing population without having to increase the use of land, water, and fertilizers to unsustainable levels."
According to Sundaresan, the findings might be applied to other food crops. In particular, rice serves as a genetic template for other cereal crops like maize and wheat, which together make up important global food staples.
The study was published in Nature on December 27.
Introducing asexual reproduction through seeds – apomixis – into crop species could revolutionize agriculture by allowing F1 hybrids with enhanced yield and stability to be clonally propagated. Engineering synthetic apomixis has proven feasible in inbred rice through the inactivation of three genes (MiMe), which results in the conversion of meiosis into mitosis in a line ectopically expressing the BABYBOOM1 (BBM1) parthenogenetic trigger in egg cells. However, only 10–30% of the seeds are clonal. Here, we show that synthetic apomixis can be achieved in an F1 hybrid of rice by inducing MiMe mutations and egg cell expression of BBM1 in a single step. We generate hybrid plants that produce more than 95% of clonal seeds across multiple generations. Clonal apomictic plants maintain the phenotype of the F1 hybrid along successive generations. Our results demonstrate that there is no barrier to almost fully penetrant synthetic apomixis in an important crop species, rendering it compatible with use in agriculture.
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