Flooding may no longer damage rice plants

Published in The Hindu on August 21, 2009

Scientists have found a novel way to overcome the challenge of cultivating rice in flood-prone areas. Globally, about 25 per cent of rice-producing land gets affected by flooding. The problem is particularly acute in many Asian countries. Most rice plants would die if they remain submerged in water for just three days.

One way is to ensure that the stem grows in response to the water level so that the leaves are always above water. Deepwater rice cultivated in lowland areas prone to flooding already exhibit this characteristic. But these varieties have low yields. The first challenge was to identify the genes that enable stem growth in response rising water level.

In a paper in the Nature journal, a team led by Motoyuki Ashikari of Nagoya University, Japan, has found two genes — SNORKEL1 and SNORKEL2 — responsible for stem elongation in response to rising water level. The two genes can together trigger growth of up to 8 metres when water level keeps rising.

The two genes are normally in a dormant state and get expressed (active) only in response to ethylene accumulation. Ethylene accumulation occurs in rice plants only in deep-water conditions. The paper notes that ethylene content increases by 25-fold within 24 hours. The two genes that get expressed in response to ethylene accumulation ensures that a rapid shooting up of plants.

Scientists have come very close to making high-yielding rice varieties grown by farmers to exhibit this characteristic. The scientists note that non-deepwater rice varieties tend to behave like deepwater rice when the two genes are introduced into them.

Another group of scientists had in 2006 found another gene (SUB1A) that allows rice to survive under flooded conditions. Unlike the SNORKEL genes, the SUB1A gene works by restricting plant elongation in the face of flash floods at the seedling stage. The SUB1A gene produces shunted plant that can survive in water for a few weeks. The SNORKEL genes and SUB1A have opposing functions in regulating plant growth in response to flooding, notes the Nature paper.

Pamela Ronald at the University of California, who was one of the authors who identified the SUB1A gene, and another scientist succeeded in transferring the SUB1A gene in to a popular high-yield rice variety known as Swarna. The new varieties Swarna-Sub1 and IR64- Sub1 were field tested in India and Bangladesh.

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