The genetic ark in the rice bowl
The Ayeyarwady Delta is Myanmar's "rice bowl," a vast and fertile plain responsible for a huge portion of the nation's rice production. Yet, this agricultural heartland is seasonally inundated by monsoons, with flash floods that can submerge entire fields. For centuries, farmers cultivated traditional rice varieties, or landraces, that were uniquely adapted to these stressful conditions. These local cultivars are a large source of genetic diversity.
Beginning in the 1960s, the Green Revolution introduced modern high-yielding varieties (HYVs) to the region. While these new types of rice promised larger harvests, they performed best under optimal conditions and often lacked the resilience of the traditional strains. Farmers, seeking to increase output, began to abandon the landraces their families had cultivated for generations. In the lower Ayeyarwady Delta, local varieties still make up a significant portion of crops, but in the upper delta, HYVs now occupy 98% of rice fields. This shift threatened to erase the unique genetic traits for flood and salt tolerance that had evolved in the delta's specific environment. Recognizing this danger, scientists began preserving these landraces in gene banks, such as the Department of Agricultural Research in Yezin, Myanmar, and the International Rice Research Institute (IRRI) in the Philippines.
A gene that holds its breath
The way to survive a flash flood is a specific gene known as SUB1A (Submergence-1A). This gene was first identified in an Indian landrace called FR13A, but its variants are present in many traditional Southeast Asian cultivars. Rice plants containing the SUB1A gene respond to complete submergence by entering a state of suspended animation. They halt their growth, conserving energy until the floodwaters recede. This strategy allows them to survive underwater for up to two weeks. In contrast, varieties without the SUB1A gene panic; they rapidly elongate their stems and leaves in a futile attempt to reach the surface, exhausting their energy reserves and perishing within days.
Researchers have used a technique called marker-assisted breeding to introduce the SUB1A gene into modern, high-yielding rice varieties without altering their other desirable qualities. This process has created new "scuba rice" strains, such as Swarna-Sub1, which combine the high productivity of modern rice with the flood resilience of the old landraces. Following floods, these SUB1 varieties can have a yield advantage of one to three tons per hectare over intolerant cultivars. This blending of old and new genetics helps ensure ensuring food security in regions like the Ayeyarwady Delta that are increasingly vulnerable to extreme weather.