Recent headlines read: Cold spell compounds woes of Palestinian farmers; Cold spell hits farmers in Nueva Vizcaya, Philippines; and Longest-ever cold spell hits northern Vietnam.
Behind these headlines are agricultural crops placed in jeopardy, especially rice, which is originally a plant that has no builtin mechanism against cold.
Because of centuries of genetic selection, some rice varieties can already be grown in areas where the temperature is low. Of the two major groups of rice, japonica varieties can thrive better in temperate regions than indica varieties, which are more common in hot and humid areas. Hence, japonica rice is widely grown in temperate and subtemperate countries, the Southern Cone of South America, the Mediterranean climate zone, and high-altitude areas in the tropics.
About 20 percent of the rice areas worldwide are planted with temperate rice, which comes from countries as diverse as Australia, Turkey, Japan, China, Republic of Korea (South Korea), Democratic People’s Republic of Korea (North Korea), Uzbekistan, India, Kazakhstan, Bangladesh, Tanzania, Madagascar, and the United States.
And, the demand for cultivating temperate japonica rice may increase because of some erratic changes in climate in some parts of the world. To cite an example of an extreme weather change, in December 2009, Orissa State in India, known for its hot and humid climate, was gripped by a cold wave that dipped as low as 8 °C. This drop in temperature set a new record in the state within a period of 50 years.
Cold damage
Although japonica rice varieties in Japan and Korea produce higher yields, when cold temperature blows its chilly air and remains during the critical stage of the crop’s development, it is like a silent curse with its destructive spells, and it determines rice’s fate: a less productive season.
In South Korea, for example, marked drops in temperature in 1971, 1980, and 2003 damaged 17%, 80%, and 20% of its total rice area, respectively. In 1980, yield loss in milled rice hit 3.9 tons per hectare. In China alone, the recorded yield loss per year because of cold is 3–5 million tons. More recently, in Vietnam, the 30-day cold spell that hit in February 2008 reportedly destroyed more than 53,000 hectares of rice.
Needless to say, cold temperature is one of the major environmental stresses in rice production.
No pollen, no grain
According to Kshirod Kumar Jena, plant breeder and International Rice Research Institute (IRRI) country representative for Korea based in Suwon, cold temperature can damage rice in its germination stage, seedling stage, and/ or reproductive stage. However, a drop in temperature during rice’s early vegetative stage until its grain-filling stage causes the most severe damage. Dr. Jena explained that cold stress hinders rice plants from forming fertile pollen that is crucial for fertilization. Consequently, they fail to produce grains, which leads to a decrease in yield or, worse, no yield at all.
Moreover, Dr. Jena mentioned that low temperature impairs seed germination, reduces seedling vigor, weakens rice’s photosynthetic ability by inducing leaf discoloration, reduces plant height, produces degenerated spikes, delays days to heading, reduces spikelet fertility, promotes irregular grain filling and maturity, and leads to poor grain quality.
It’s in the genes
Rice breeders see no other way to reduce cold-related losses in rice production than genetically improving cold-sensitive cultivars using modern breeding techniques. The sequencing of the rice genome and the development of marker-assisted selection (MAS) have fast-tracked their research efforts.
“Cold tolerance is a complex trait; it is controlled by many different genes,” Dr. Jena said. “But now, it has become easy to identify the correct DNA markers linked to the quantitative trait loci (QTLs) conferring cold tolerance.” By developing desirable mapping populations and accurate phenotyping for cold-tolerance and -sensitive traits, and conducting QTL analysis, Dr. Jena and his team were able to identify three QTLs or genomic regions from chromosomes 3, 7, and 9—QTLs that have a direct link to cold tolerance at the reproductive stage. Through this, they identified markers that linked the QTLs to seed fertility.
IRRI started collaboration with South Korea’s Rural Development Administration (RDA) using the International Rice Cold Tolerance Nursery (IRCTN) in 1978. However, recently, in collaboration with RDA’s National Institute of Crop Science, a new source was discovered, a cold-tolerant breeding line—IR66160-121-4-4-2—that inherited cold-tolerance genes from Indonesia’s tropical japonica cultivar Jimbrug and northern China’s temperate japonica cultivar Shen-Nung89-366. Using this line, Dr. Jena and his team from RDA, namely, Jung-Pil Suh, Ji-Ung Jeung, Jung-Il Lee, Jong-Doo Yea, Jeong- Hee Lee, YeonGyu Kim, and Jin-Chul Shin, produced recombinant inbred lines (RILs) by crossing cold-tolerant and cold-sensitive cultivars. They then evaluated these RIL progenies under two conditions: one, by subjecting them to cold-water stress at 18–19 °C in the field; two, by exposing them to cool air temperature in the greenhouse at 18 °C. After the experiment, they selected some promising cold tolerant lines that also have desirable seed fertility and early maturity traits.
Concerted efforts
To further strengthen international efforts to develop cold-tolerant varieties, IRRI established the Temperate Rice Research Consortium (TRRC) in 2007. Its country members are Australia,Bhutan, Chile, China, Egypt, Japan, Kazakhstan, Nepal, the Philippines, Russia, South Korea, Spain, Tanzania, Uruguay, Uzbekistan, and the U.S. Dr. Seong-Hee Lee, Korean member of the IRRI Board of Trustees, was instrumental in the formation of this Consortium, bringing along with him the full financial support of the RDA. A steering committee and four working groups were formed. Each working group focused on one of the four major constraints identified for temperate rice: (1) yield potential and grain quality, (2)blast resistance, (3) cold tolerance, and (4) nitrogen and water use efficiency.
The third group, in particular, aimed to evaluate a selected number of cold-tolerant germplasm accessions provided by working group partners at seedling and reproductive stages and identify promising cultivars or breeding lines at key sites; combine cold-tolerant genotypes with coldsensitive cultivars and develop suitable cold-tolerant germplasm adapted to different countries; use potential DNA markers linked to cold-tolerance traits for marker-assisted breeding; develop a common set of cold-tolerant lines for use in breeding in collaboration with working group partners; and provide training opportunities to young researchers by monitoring key sites and visiting advanced cold tolerance breeding laboratories.
According to Ms. Thelma Padolina, plant breeder at the Philippine Rice Research Institute (PhilRice), one of the benefits of being a member of the working group is that breeding materials can now be thoroughly screened [as PhilRice does not have a screening facility]. Before, they just relied on observing plants’ physical reactions, which are mostly erratic. Another benefit is that they will be able to infuse genetic diversity by making other sources of germplasm from other countries available for breeding. “The varieties that we were able to develop still lack the necessary traits,” she said. “They are specific to a season and to the developmental stage of the plant and lack biotic and abiotic stress tolerance.”
Collaboration with Bangladesh
Farmers in flood-prone areas of Bangladesh cannot usually plant rice during the rainy season. And, after the rainy season, during November to December, when the water subsides, the soil is more fertile because of the nutrients brought in by the flood. But, there is another problem―cold.
To solve this problem, Dr. Jena has started collaborating with the Bangladesh Rice Research Institute to develop cold tolerant varieties for boro or winter season cultivation. Several cold-tolerant lines have already been produced from a cross between BR29, a popular cold sensitive variety in Bangladesh, and Jinbu, a cold-tolerant variety from Korea. These generated cold-tolerant lines will be useful for rice breeders in their selection for varieties suitable to their specific locations.
Bangladesh is only one of the countries that the TRRC is extending its hand to. More countries benefit from the sharing of this cold-tolerant germplasm. And, all these efforts boil down to improving the quality of life for farmers in cold-prone areas, just like those in cold-affected areas in Kayapa, Nueva Vizcaya, Philippines (see Cold reality).
Cold-tolerant rice is indeed a necessary product for cold-prone areas. Thus, it goes without saying that IRRI’s and its partners’ concerted efforts through an effective channel, the TRRC, in combating the devastating effects of cold should clearly increase the productivity of about one-fifth of the rice-growing areas in the world.
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Ms. Reyes is the managing editor of Rice Today
