Bangladesh and India are the two most vulnerable areas to climate change in South Asia. During floods, farmers in Bangladesh and India lose up to 4 million tonnes of rice per year—enough to feed 30 million people. Submergence can affect rice crops at any stage of growth, either short-term (flash floods) or long-term (stagnant flooding). Chances of survival are extremely low when completely submerged during the crop’s vegetative stage. During flooding, the rice plant elongates its leaves and stems to escape submergence, but high-yielding modern varieties cannot elongate enough. If floods last for more than a few days, the rice plants expend so much energy trying to escape that they are unable to recover.
Plant breeders have discovered that a single gene, the SUB1 gene, confers resistance to submergence of up to 14 days. Scientists were able to isolate this gene, derived from an Indian rice variety, and identify the genetic code that controls submergence tolerance. The SUB1A gene activates when the plant is submerged, making it dormant and conserving its energy until the floodwater recedes. Improved varieties incorporated with the SUB1 gene have shown a yield advantage of 1–3 tons following flooding for 10–15 days. The project Stress-Tolerant Rice for Africa and South Asia (STRASA) began at the end of 2007 with the International Rice Research Institute in collaboration with AfricaRice to develop and deliver rice varieties tolerant of abiotic stresses to the millions of farmers in the unfavorable rice-growing environments. Flood-tolerant varieties that have been released through STRASA and are now being planted include Swarna Sub1 in India and Samba Mahsuri in Bangladesh.
Relationship to CSA
Aggravating floods are among the most ascertained impacts of climate change in many rice growing regions. East India and Bangladesh have been battered by several tropical cyclones in recent years. Increasing sea levels will further increase flooding risks in coastal areas and deltas. In addition to water depth, higher sea levels increase the duration of flooding which is typically the decisive feature to determine survival rate of rice plants. Flood-tolerant rice varieties are effectively the only adaptation options under such hazardous circumstances of intense flooding events. One impact assessment study showed that SUB1 can deliver both efficiency gains, through higher and less variable yields; and equity gains in disproportionately benefiting marginal, lower caste groups of farmers heavily occupying these areas.
Impact and lessons learned
Plant breeding has a long track record of improving resilience of rice production systems to climatic extremes. New approaches of (non-GMO) ‘precision breeding’ allow the introgression of specific traits into any given variety while its ‘genetic background’ remains largely intact. In turn, the new version of this variety will not need any change in cop management and also will maintain the grain quality traits. By choosing popular varieties for genetic improvement, this approach will not face any problem in farmers’ acceptability of improved seeds.