A gene discovery by Chinese scientists paves the way for the machine production of hybrid rice seeds

“For next generation hybrid seed Productionthe use of small-grain male sterile lines to mechanically separate small hybrid seeds from a mixed crop is promising,” they said.

The challenge was to find a gene that would allow a rice line to have a small grain size without reducing seed number and yield.

However, the team found that this was possible thanks to the “ideal grain size gene” GSE3. Field tests showed that rice lines with the gene did not negatively affect hybrid seed numbers; in fact, it resulted in an increase of 21 to 38 percent.

China was a pioneer hybrid rice, where rice is bred from two genetically different parents and results in significantly higher rice yields. The first high-yielding commercial strains were created in China, and that country is now the world’s largest producer and consumer of hybrid rice.

“The yield of rice has increased by 20 to 30 percent in the last few decades due to the use of hybrid rice, which has greatly contributed to food security” said the team.

Hybrid rice is the first generation of offspring of a rice plant that is fertilized with the pollen of a genetically different rice plant, achieved by pollinating a sterile male line with a self-pollinating renewal line.

“A number of restaurateurs must be adult near the male sterile line in separate rows to ensure enough pollen for hybridization. To prevent seed contamination, manual labor is used to remove the recovery line before harvesting the hybrid seeds, resulting in the production of over 150,000 tonnes of seed. wasted in China every year, the team wrote.

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An ideal approach to this would be to plant a mixture of sterile and restorer lines and harvest all the seeds together, before mechanically separating the hybrid seeds from the restorer seeds.

Methods to achieve this have been proposed – such as sorting by color – but they have “inherent flaws”, the researchers said.

It was suggested that reducing the male sterile line, which would produce smaller hybrid seeds, and increasing the recovery line would allow mechanical separation using a “simple sieve,” the team said.

The team crossed the Tianyouhuazhan (TYHZ) ‘super hybrid rice’ variety with a number of others. They found that crossing with the small-grain variety Xiaoligeng resulted in a smaller male-sterile line, which they later identified thanks to the GSE3 gene.

A new male sterile line, called Xiaoqiao A (XQA), was bred with a large grain size recovery line they had previously created called Da huazhan (DHZ). The first generation of hybrid seeds produced by this cross were smaller, allowing them to be mechanically separated from the larger seeds produced by self-pollination of the renewal line.

They found that at sieve opening widths below 2.08 mm (0.08 in), the purity of hybrid seeds screened by grain thickness was around 96 percent, meeting standards for commercial production. By comparison, traditional separation methods are 96 to 98 percent pure, according to the paper.

While hybrid seed yield was lower, the team found that the number of seeds per plot was higher using the XQA and DHZ lines, which is important because it “is a determinant of commercial hybrid seed production.”

“Thus, these field trials demonstrate that ideal male sterile lines (XQA) and restorer lines (DHZ) allow for fully mechanized hybrid rice breeding,” the team wrote.

However, generating rice lines with the GSE3 gene is still a challenge because conventional breeding approaches are also time- and labor-intensive. To get around this, the team “developed a one-step method to generate loss-of-function mutants of GSE3” using a well-known gene-editing tool. CRISPR-Cas9.

Outside ricethe researchers said GSE3 could also potentially be used in other crops to improve male sterile lines for mechanized hybrid seed production.

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