Deepwater rice

Deepwater rice are varieties of rice (Oryza sativa) grown in flooded conditions with water more than 50 cm (20 in) deep for at least a month.^[1] More than 100 million people in Southeast Asia including Northeastern India rely on deepwater rice for their sustenance.

Deepwater rice is cultivated less in West Africa than in Asia, with about 4,700 km² (1,800 sq mi).[7] Areas it is grown include the Niger River basin.^[6] Some areas in Ecuador grow deepwater rice.^[8]

Cultivation methods

Deepwater rice is grown in tropical monsoon climates normally around river deltas and their floodplains mainly in backswamps and natural levees. The nature of the flood is important for success of deepwater rice, with timing and the rate of rise of water affecting survival and crop density. Generally, the flood water comes from rainfall or rises in the water table. In places with low rainfall, water overspilling from rivers can flood rice-producing areas.

Issues

When seeds are sown directly into the soil, the seeds and young plants can be damaged by drought conditions before floods arrive. During this stage, the plants can also suffer due to competition from weeds. Sudden flooding, where a large volume of water enters the field in a short time, can lead to a high level of seedling death.^[8]

Floating rice faces additional problems due to the depth and time of the water in which it grows. Water conditions such as turbulence and temperature can adversely affect the crop.^[9]

Natural disasters can also damage or destroy deepwater rice crops.

Deepwater rice emits the least methane, a greenhouse gas, of the wetland rice ecologies, producing approximately one third of emissions compared to paddy field rice.

Floating rice adaptation

Floating rice is planted in dry ground and allowed to establish as young plants. The area becomes flooded which triggers the rice's elongation ability. This means when a field where rice is growing floods, accelerated growth in the

The elongation is triggered when the plant is submerged through a mechanism involving ethylene gas. Ethylene is normally produced by plants and diffused into the air, but when floating rice is submerged in water, this process is disrupted as the gas moves more slowly into water. This leads to a buildup of ethylene in the plant. This triggers the production of a hormone called gibberellin which causes the rapid growth in the plant. When the plant reaches the surface, the ethylene gas can escape as normal and the rapid growth stops.^[11] Research continues to enhance the ability to cope with increasing water depth.^[12] Rice will drown if submerged for too long.^[13]

New cultivars

A recent cultivar named Swarna Sub1 was developed via marker-assisted selection, with the ability to withstand prolonged periods of around 14 days beneath a flooded plain.^[14][15] The submergence tolerance ability of this variety is conferred by the presence of the Sub1A gene, introgressed from the Indian cultivar FR13A into the flood-vulnerable (but high yielding) cultivar Swarna.^[14][15]

Swarna Sub1 effectively enters a dormant, energy-conserving state upon being submerged in a flooded rice paddy, a process that involves the finely controlled

• Upland rice
• Rice-fish system

References