"Waterproof" versions of popular varieties of rice, which can withstand 2 weeks of complete submergence, have successfully passed
tests in farmers' fields in India and Bangladesh, and can tackle the problem of major crop losses due to flooding.
The flood-tolerant versions of the "mega-varieties" of rice, which are high-yielding varieties popular with both farmers and consumers that are grown over huge areas across Asia, are effectively identical to their susceptible counterparts, but recover after severe flooding to yield well.
Several of these varieties are now close to official release by national and state seed certification agencies in India and Bangladesh, where farmers suffer major crop losses because of flooding of up to 4 million tons of rice per year. This is enough rice to feed 30 million people.
The new varieties were made possible following the identification of a single gene that is responsible for most of the submergence tolerance.
Thirteen years ago, Dr David Mackill, senior rice breeder at the International Rice Research Institute (IRRI), then at the University of California (UC) at Davis, and Kenong Xu, his graduate student, pinpointed the gene in a low-yielding traditional Indian rice variety known to withstand flooding.
Xu subsequently worked as a postdoctoral fellow in the lab of Pamela Ronald, a UC Davis professor, and they isolated the specific gene, called Sub1A, and demonstrated that it confers tolerance to normally intolerant rice plants. Dr Ronald's team showed that the gene is switched on when the plants are submerged.
"Sub1A effectively makes the plant dormant during submergence, allowing it to conserve energy until the floodwaters recede," according to Dr Julia Bailey-Serres, a geneticist from UC Riverside, who is leading the work to determine exactly how Sub1A confers flood tolerance.
Typically, rice plants will extend the length of their leaves and stem in an attempt to escape submergence. The Sub1A gene is an evolutionarily new gene in rice found in only a small proportion of the rice varieties originating from eastern India and Sri Lanka.
The activation of this gene under submergence counteracts the escape strategy. "The potential for impact is huge. "In Bangladesh, for example, 20 per cent of the rice land is flood prone and the country typically suffers several major floods each year," said Dr Mackill.
"Submergence-tolerant varieties could make major inroads into Bangladesh's annual rice shortfall and substantially reduce its import needs," he added.
