climate ready rice

8/7/2019 Climate ready rice

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Climate-ready rice

Rice varieties that can withstand drought, flood, heat, cold, or soil problems like high salt and iron toxicity, helppoor farmers curb yield losses.

Drought | Submergence | Cold | Heat | Salinity | Poor soils

Rice varieties that can withstand environmental stresses ² drought,flood, heat, cold ² or soil problems like high salinity and iron toxicity, help farmers curb their losses and retainharvest levels even under unfavorable environments.

Environmental stresses constrain rice production, affecting about 30% of the 700 million poor in Asia alone, wholive in rainfed rice-growing areas. These stresses can be caused by extreme climatic changes like drought, floodingor rising sea levels, while some can be inherent like high iron toxicity in the soil. Our breeding programs aim todevelop rice types that can survive in these harsh environments.

IRRI breeders use a ³precision breeding method known as marker-assisted breeding. A marker is a DNA segmentlocated close to an allele ± or a version of a gene or controlling factor for an important trait. Breeders use thesemarkers to select for a favorable allele and then backcross generations and select offsprings showing trait stability.This method shortens the breeding process, producing a promising line in about two years, whereas breedingseveral generations of rice to maturity takes much longer. It has also greatly improved the precision with which

specific desirable traits can be moved from one rice variety to another.

In recent years, IRRI has provided improved rice lines tolerant to drought, submergence, cold, salinity, andsodicity. Our national research and agricultural extension partners test these lines in different locations andcountries, including evaluating their performance on farmers¶ fields through participatory varietal selection. Theselected lines which survive under stress and retain desirable grain qualities are either released directly or bred into

widely grown local varieties or ³mega-varieties.´

Along with improved crop management, proper use of technology through extension work, and the support of national institutions, these improved varieties or ³climate-ready rice´ are showing substantial, positive impacts inthe lives of poor farmers.

Drought-tolerant rice



Drought is the most widespread and damaging of all environmentalstresses, affecting 23 million hectares of rainfed rice in South and Southeast Asia. In some states in India, severedrought can cause as much as 40% yield loss, amounting to $800 million.

IRRI has developed drought-tolerant varieties which have been released in several countries and are now beingplanted by farmers. These include Sahbhagi dhan in India, the ³5411´ variety in the Philippines, and the Sookhadhan varieties in Nepal. Across these varieties, the average yield advantage of drought-tolerant varieties over

drought-susceptible ones is 0.8-1.2 ton per hectare under drought.

IRRI scientists have identified several quantitative trait loci (QTLs) that confer drought tolerance and improve ricegrain yield under drought. Drought tolerance is introduced in popular high-yielding but drought-susceptible ricevarieties IR64, Swarna and Vandna through introgression and pyramiding of major drought-yield QTLs, following

marker-assisted backcrossing.

Molecular and physiological studies to decipher the mechanism of tolerance in identified QTLs are under way toget a better insight of this complex trait.

Submergence-tolerant rice

Submergence can affect rice crops at any stage of growth, either short-term (i.e., flash floods) or long-term (stagnant flooding). The chances of survival are extremely low whencompletely submerged during the crop¶s vegetative stage. During floods, farmers in Bangladesh and India lose upto 4 million tons of rice per year²enough to feed 30 million people. In 2006, the Philippines lost harvests worth$65 million to floods.

During flooding, the rice plant elongates its leaves and stems to escape submergence. Deepwater rice varieties areable to do this rapidly enough to survive. High-yielding modern varieties cannot elongate enough. If flood lasts for

more than a few days, they expend so much energy trying unsuccessfully to escape that they¶re unable to recover.

Plant breeders have discovered that a single gene, the SUB1 gene, confers resistance to submergence of up to 14days. Scientists were able to isolate the SUB1A gene, derived from an Indian rice variety, and identify the geneticcode that controls submergence tolerance. The SUB1A gene activates when the plant is submerged, making it

dormant and conserves its energy until the floodwater recedes.



Improved varieties incorporated with the SUB1 gene have shown a yield advantage of 1±3 tons following floodingfor 10±15 days. Flood-tolerant varieties that have been released and are now being planted include Swarna Sub1 inIndia, Samba Mahsuri in Bangladesh, and IR64-Sub1 in the Philippines.

Cold-tolerant rice

Frequently occurring low temperature causes more than 30% grain loss.Diseases such as blast and sheath brown rot adds to the damage especially when it attacks at the plant¶s earlyvegetative stage. In China, the recorded yield loss due to low temperature is 3-5 million tons. In 1980, Korea lost

an average yield of 3.9 tons per hectare, more than half of its annual yield per hectare.

Cold tolerance is a complex trait controlled by many genes. Now, plant breeders can identify the correct DNAmarkers linked to the quantitative trait loci (QTLs) ± a gene or chromosomal region that affects a quantitative trait± that confers cold tolerance. IRRI scientists have identified three QTLs or genomic regions that have a direct link to cold tolerance at the plant¶s reproductive stage. Through these QTLs, they identified markers that linked theQTLs to seed fertility. Cold stress hinders rice plants from forming fertile pollen that is crucial for fertilization andcan consequently fail to produce grains.

IRRI¶s collaboration with South Korea¶s Rural Development Authority paved the discovery of a cold-tolerantbreeding line²IR66160-121-4-4-2²that inherited cold-tolerance genes from Indonesia's tropical japonica cultivar

Jimbrug and northern China's temperate japonica cultivar Shen-Nung89-366.

Using this line, IRRI produced recombinant inbred lines (RILs) by crossing cold-tolerant and cold-sensitive rice

lines. Scientists then evaluated these RIL progenies under two separate conditions ± cold-water stress and cool air temperature. After the experiment, they selected some promising cold tolerant lines that also have desirable seed

fertility and early maturity traits.

These breeding efforts form part of a bigger research initiative under the Temperate Rice Research Consortium, agroup of national and international institutions collaborating in research, training, and technology-generation toovercome the constraints of temperate rice production.

Heat-tolerant rice

Global warming has a significant effect on rice production. Though riceoriginates from the tropics, high temperature (over 35 oC) during the reproductive stages reduces rice production,especially when the rice plant flowering occurs at such a high temperature, which causes low seed setting and low



yield. Higher night temperatures during the ripening stage also decrease rice yield and grain quality. Further, evenat the vegetative growth stage, heat stress can cause leaf yellowing and accelerated development, leading to lowyield potential in sensitive rice varieties.

Rice plants are most sensitive at the flowering and ripening stages. Both yield and grain quality are adverselyaffected. IRRI scientists are identifying donors for tolerance of high temperature by screening improved andtraditional rice varieties. These donors are used in a crossing program to incorporate tolerance of high temperatureinto elite rice lines that are then tested for heat tolerance in µhot and dry¶ and µhot and humid¶ countries. QTLs arebeing mapped to facilitate varietal development using marker-assisted selection and shuttle breeding strategies.

Another mechanism for rice heat tolerance is early-morning flowering, which escapes the high temperature atmidday. It was found that O. glaberrima, a wild species of rice, is a useful genetic source since it has a habit of early-morning flowering and high transpiration with sufficient water, both of which are convenient traits for avoiding heat stress. IRRI scientists are looking into the causes of this useful trait through physiological and

genetic studies.

Salt-tolerant rice

Million hectares of land suited to rice production in Asia and Africa are currently unexploited because of high saltcontent. Rising sea levels brings salt water further inland, contributing to soil salinity. In Bangladesh¶s coastalareas, salinity affects about one million hectares of land that can otherwise be used for rice farming. Riceproductivity in salt-affected areas is very low ² less than 1.5 ton per hectare. But this can potentially increase byat least two tons per hectare with improved varieties that can withstand soil salinity.

IRRI scientists have identified a major quantitative trait loci (QTL) labeled as Saltol which can confer hightolerance to salinity. This and other QTLs for tolerance during a rice crop¶s seedling stage and for the reproductive

stage are targeted to develop varieties tolerant at both stages.

The same approach used for developing submergence-tolerant mega-varieties is being used with the Saltol locus

for salinity. This is particularly targeted at coastal areas during the wet season where both salinity and submergenceare problems. Recent work at IRRI has shown that the SUB1 gene and Saltol can be combined in the same

genotype. Thus, these lines combine tolerance of both stresses.

Plant breeders have incorporated Saltol in popular rice varieties such as the BRRI Dhan 11, 28, and 29 varietiesreleased in Bangladesh, as well as popular varieties in West Africa. To date, IRRI, with the help of its nationalpartners, has developed more than 100 salinity-tolerant elite lines. These elite lines possess superior traits such ashigh yield, good eating quality, resistance to pests and diseases, and tolerance of stresses, and are ready for testing

in farmer¶s fields.



Varieties that withstand problem soils

Nutritional imbalances such as potassium and zinc deficiency and iron and aluminumtoxicity are widespread in most rice production areas in Asia, Latin America, and Africa. Genetic donors for tolerance of these soil problems are being identified while being physiologically and genetically characterized, andthe major QTLs identified and used in breeding.

Iron toxicity is a widespread growth constraint in lowland rice in Africa. IRRI has identified highly tolerant

varieties or lines such as Suakoko 8 ( O. sativa) and CG 14 ( O. glaberrima). The Africa Rice Center (AfricaRice),IRRI¶s partner in the region, has facilitated the release of some improved varieties that are tolerant of iron toxicity.

At AfricaRice, breeding is under way to validate tolerance to iron toxicity and to identify new QTLs for use in

marker-assisted selection.

climate ready rice

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