Rice plants normally grow well in still water. But most will die if they are completely underwater for more than four days. Now, researchers have identified a gene   that helps rice survive longer underwater. They say the discovery will lead to new kinds of rice plants that can survive flooding, and therefore reach their final aim, ensuring more dependable food supplies. Tests are now being done in prefix = st1 /Laos,BangladeshandIndia. The researchers say experimental rice plants with the gene have survived underwater as long as two weeks. When flooding happens, most kinds of rice plants cannot get enough oxygen, carbon dioxide or sunlight. But the scientists say crop loss depends on several conditions. These include soil conditions and plant age. Others include the amount of time the plant is underwater and the amount of fertilizer   used on the crop.  On a genetic   map of rice, the scientists became interested in a group of three genes. They experimented with one of them, a gene known as Sub-One-A. They found that when this gene becomes very active, it improves the ability of rice to survive longer when rice is covered by water. They believe it succeeds because it affects the reaction to hormones  .  _ control the ability of a flooded plant to survive. Placing the gene into rice plants that are especially good for conditions inIndia, researchers say the genetically engineered plants not only survived but also produced good crops. The researchers are now trying to identify all the genes governed by the Sub-One-A gene. Being able to leave water on rice plants for an additional week might also help farmers prevent the growth of weeds. Less weed growth around their crops would mean less need for herbicide   chemicals. What is the final aim of this research?
To identify the gene that helps rice survive underwater. To increase the ability of rice to fight against floods. To help farmers spend less time removing weeds. To make sure of enough food supplies.