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Scuba Rice
Climate change threatens to cause increased flooding of the fields of rice farmers. Scuba rice, formally known as ‘Sub1,’ are cultivars of a new, advanced type of rice that is flood tolerant. These innovative cultivars are able to withstand flooding for up to 15 days, triggered by a variant of a gene called Sub1A (Submergence 1A) introduced by traditional breeding from flood-tolerant rice (2). Currently very popular in wet Asian climates, in particular India and Bangladesh (2), this variety of rice has the potential to benefit farmers in coastal areas or any regions susceptible to flooding.

Description
Scuba rice is a cultivar of Asian rice (Oryza sativa L.) in which genetic variants at the Submergence 1 locus (Sub1, in particular Sub1A-1) have been introduced by breeding from a flood-tolerant rice cultivar into flood-sensitive cultivars allowing the resulting cultivars to be more tolerant to flooding (8). This type of flooding is different from the shallow flooding that is a hallmark of paddy rice, but rather weather-related flooding that submerges a considerable portion of the plant for long durations. Ethylene is a major plant hormone that regulates plant responses during environmental stress, and the Sub1A gene encodes an ethylene-response-factor-like protein that helps to regulate this response (8). The SUB1A protein causes the rice plant to go dormant during a long duration flood whereas most rice plants would spend considerable energy to elongate their stems to rise to the water surface. As a result, following receding of the water, plants containing the Sub1A genetic variant are better able to tolerant 2-3 weeks of flooding and thrive(8). Sub1A also regulates other genes including those involved in oxidative stress tolerance (9). The rice cultivars in which the Sub1A was introduced into include Swarna, Sambha, Mahsuri, IR64, BR11, CR1009 and Thadokkam 1 (5).

History
FR13A has long been a traditional Indian rice cultivar that could withstand up to 14 days of flooding. The cultivar was lacking success in yield and taste. In the 1990s, David Mackill, working between the International Rice Research Institute (IRRI) and the University of California wanted to adapt rice to become more flood tolerant, but also appealing to people living in areas susceptible to flooding. The development of marker-assisted selection (MAS) allowed Mackill and his U.S. collaborators including Pamela Ronald and Julia Bailey-Serres to conduct genetic based research. In 2006, the team reported the successful in isolation of the gene that is responsible for conferring flood tolerance in FR13A (9). Submergence 1A (Sub1A) was the name given. From there, the Sub1 chromosome region was introduced into the following Asian rice cultivars using genetic markers to guide the breeding: IR64, Swarna and Samba Mahsuri (2).

A year later, field trials were conducted in Bangladesh with Swarna-Sub1. Tests were successful, for example as noted by Mostafa Kamal, a farmer responsible for feeding 22 family members. After a summer flood lasting of 15 days, the trial showed that 95-98% of the Scuba plants recovered after the water resided, whereas only 10-12% of cultivars that did not contain the Sub1 variant survived the floods. Kamal’s neighbor, Mohammad Shadidul Islam, was ecstatic about the results. “These varieties will mean more food, higher income, and a better livelihood (2).” After successful testing, new cultivars with the valuable genetic region were officially released in 2010 to various Asian countries including India, the Philippines and Bangladesh (4).

Farming
There are a few important tactics that are required along with regular cultural practices to allow for maximum production of rice. The International Rice Research Institute (IRRI) provides an extraordinary review for crucial practices to ensure growth of all rice varieties; titled, “Rice Knowledge Bank,” the IRRI provides information on seed selection, soil preparation, water, fertility and pest management, as well as harvesting and storing. Reviewing each category allows for greater success in all aspects of growing rice (7).

Moving Forward
The advancement of Scuba Rice has sparked great optimism around the world, particularly in Asia and Africa. Bangladesh for example, is one of the most flooded countries in the world and 20% of its rice plants are susceptible to flooding (2). In Philippines in 2006, major typhoons caused an estimated US $65 million dollars in crop damage (4). Two countries in Western Africa, Sierra Leone and Liberia, both receive an average of over 2000 mm of precipitation annually. Canada has an average of just 530 mm (3). With climate change looming, the need for such crops such as scuba rice is a necessity. It is estimated that 50% of yields and 18 million households will benefit because of Scuba Rice in the next ten years (4).