Public Release:  Wild parent spawns super salt-tolerant rice

International Rice Research Institute

Farmers are set to reclaim salt-ravaged land thanks to a single rice plant born of two unlikely parents that is spawning a new generation of rice that has double the salinity tolerance of other rice.

"This will make saline-stricken rice farms in coastal areas usable to farmers," said lead scientist Dr. Kshirod Jena of the International Rice Research Institute (IRRI). "These farmlands are usually abandoned by coastal farmers because the encroaching seawater has rendered the soil useless. That means livelihood lost for these communities."

Unlike regular rice, the new rice line can expel salt it takes from the soil into the air through salt glands it has on its leaves, explained Dr. Jena.

The new rice was bred by successfully crossing (or mating) two different rice parents - the exotic wild rice species Oryza coarctata and rice variety IR56 of the cultivated rice species O. sativa. What is extra special about this breakthrough is that O. coarctata is extremely difficult to cross with cultivated rice varieties. The location of O. coarctata in the rice genome sequence is at the other end of the spectrum from that of rice varieties such as IR56.

"When we cross two types of rice with genomes so far off from each other in the genome sequence, the resulting embryo tends to abort itself," Dr. Jena said. "We've been trying to backcross these types of interspecific hybrids since the mid-1990s, but we have never been successful, until now."

The reason scientists did not give up on crossing the two types of rice was because O. coarctata is a special type of rice that grows in brackish, salty water - making it highly resistant to saltiness in the soil. According to Dr. Jena, O. coarctata can tolerate a higher salinity concentration (similar to that of seawater), whereas current salinity-tolerant rice varieties can cope with only half that concentration. However, O. coarctata is unsuitable for the production of edible rice.

The first sign of good news came when, out of 34,000 crosses made, three embryos were successfully "rescued." Of these three, only one embryo germinated to produce one single plant.

"We treated this single plant survivor like a baby," said Dr. Jena.

The surviving plant was then transferred into a liquid nutrient solution to ensure its survival. Once the plant was strong enough, it was grown in the field, where Dr. Jena and his team used it to backcross with IR56. Backcrossing ensures that the resulting progeny will contain all traits of IR56, and take only the desired O. coarctata trait, which is its salt tolerance.

Dr. Jena's team at IRRI is perfecting their new doubly salt-tolerant rice and will test it widely to ensure it meets all the needs of farmers and consumers. They hope to have the new variety available for farmers to grow within 4 years.

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