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Wild Parent Spawns Super Salt-Tolerant Rice

22 April 2013

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.

Rising seawater causes rice farms along coastal areas to be salty, taking away livelihoods from rice farmers.

"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.

IRRI scientists perform an embryo rescue.
Dr. Jena's team successfully rescued three embryos out of 34,000 crosses. Out of these three, one plant survived to give scientists enough material to back-cross and make sure that only the desired trait - double salt-tolerance - is acquired from the wild species.

"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.

(1) IR56 grown on normal soil (2) IR56 grown on salty-soil before crossing with O.coarctata (3) The wild O.coarctata, grown on salty soil (4) IR56 and O.coarctata's first and second generation offsprings, grown on salty soil.

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 4–5 years.

April 2013

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