Hybrid rice

Hybrid rice a hybrid produced by fertilizing an inbred rice variety having sterile pollen with pollen from rice plants of a different inbred variety that has fertile pollen. Hybrid rice therefore has two genetically different parents. As with other types of hybrids, hybrid rice typically displays heterosis (or hybrid vigor) such that when it is grown under the same conditions as comparable high-yielding inbred rice varieties it can produce up to 30% more rice.[1] High-yield crops, like hybrid rice, are one of the most important tools for combating world food crises.

The first commercial hybrid rice varieties were released in China.[2]

In crop breeding, although the use of heterosis in first-generation seeds (or F1) is well known, its application in rice was limited because of the self-pollination character of that crop. In 1974, Chinese scientists successfully transferred the male sterility gene from wild rice to create the cytoplasmic genetic male-sterile (CMS) line and hybrid combination.[3] The first generation of hybrid rice varieties were three-line hybrids and produced yields that were about 15 to 20 percent greater than those of improved or high-yielding varieties of the same growth duration.

Chinese scientist Yuan Longping,"the Father of Hybrid rice",[4] is the most famous researchers on hybrid rice. In the 1960s, he made his seminal discovery of the genetic basis of heterosis in rice. This was a unique discovery because it had been previously thought that heterosis was not possible for self-pollinating crops such as rice.[5] According to the China Daily, in 2011, Yuan developed a new hybrid rice that can produce 13.9 tons of rice per hectare.[6]

Another Chinese agronomist, Li Zhengyou, developed the Dian (or Yunnan)-type hybrid rice, and was a pioneer in the research of high-altitude hybrid rice. He published the book Dian-type Hybrid Rice (滇型杂交水稻).[7][8]

In China, hybrid rice is estimated to be planted on more than 50% of rice-growing land there and it is credited with helping the country increase its rice yields, which are among the highest within Asia. Hybrid rice is also grown in many other important rice producing countries including Indonesia, Vietnam, Myanmar, Bangladesh, India,[9] Sri Lanka, Brazil, USA, and the Philippines.[10] A 2010 study published by the International Rice Research Institute (IRRI), reports that the profitability of hybrid rice in three Indian states varied from being equally profitable as other rice to 34% more profitable.[11]

Outside of China other institutes are also researching hybrid rice, including the International Rice Research Institute, which also coordinates the Hybrid Rice Development Consortium.[12]

Potential threat

In China, the hybrid system involving limits on certain characteristics has prevented researchers finding a way to cure poor resistance to disease and pests. Moreover, hybrid rice has more frequency on having "incidence of stem borer, white back plant hopper, leaf roller, bacterial blight, sheath blight, and virus diseases".[13] "downey mildew, false smut, and kernel smut" [13] occurred on hybrid rice more. Therefore, there is a huge increase pesticide using on Hybrid rice than others. For example, in "Hunan Province", compared to normal crop, extra 31% of pesticide was used in hybrid rice.[13] Breeding process itself is also a limitation of development of hybrid rice. The cultivation of seed and high-skilled labor cost much money in the beginning, causing twenty percent of government avenue solving the gap. According to saying from famous Chinese scientist Yuan Longping, two line systems are needed to build in the future due to the limited area of plateau. Most importantly, the lack of genetic diversity has been the major problem needed to solve.

Private seeding company also has challenges dealing with hybrid rice because the process of cultivating them is very time-consuming and expensive. For example, Cargill company purchased the seed from China's government in the 1980s, the seed was produced commercially until 1992s. There are still more challenges facing in this area such as "inferior grain quality; inadequate disease/insect resistance in the first generation of hybrids; inconsistent and low seed yield; inadequate supply of pure seed of parental lines; and the high cost of seed."[14] Moreover, the IRRI policy which is a policy that is freesharing is actually limited the development of hybrid rice research. The information of technology is blocked from countries and companies, preventing the way of hybrid rice to success.

In economical and political way, the problem that hybrid rice brought is still considerable. Farmers lost their rights because the seed won't exist after harvest. They are controlled by big seeding companies. Hybrid rice for whole country is controlled by a few seeding company, bringing food safety problems.

Future directions

For future research, grain quality and resistance of insect disease have to be enhanced. Compared with Hyvs, yield of hybrids are boosted by enhancing agronomic management. Moreover, "hybrid seed production capability of parental lines" and "development of hybrids possessing higher yield potential than NPT inbred lines"[14] needs to be enhanced. In IRRI-ADB project, more researchers and workers need to be more strength and professional. Seed companies need to invest money on stuff and research, finding the most stable way to seed production and potential way to market. The Government is also encouraged to polish policy or money that can improve or boost the research of hybrid rice.

Conclusion

Hybrid rice refers to the selection of two rice varieties that are genetically different, and at the same time their excellent traits can complement each other, and the first generation of hybrids with heterosis is hybrid rice. Generally, hybrid rice refers only to the first generation of hybrids formed by crossing two sterile lines and restorer lines of the same genetic background. Large-scale popularization of hybrid rice mainly uses rice male sterile lines as genetic tools. China is the first country in the world to successfully develop and promote hybrid rice. Hybrid rice has a high degree of individual heterozygosity, and traits of hybrid progeny appear to be separated, so annual seed production is required. Corresponding to hybrid rice is conventional rice.

From October 21st to 22nd, 2019, the third-generation hybrid rice was tested for the first time in Qingzhu Village, Hengnan County, Hengyang City, Hunan Province. The yield per mu was 1046.3 kg. The third-generation hybrid rice technology is a genetically engineered male sterility line as a genetic tool, which allows all rice to theoretically find the "other half" that suits them and produce excellent offspring.

References
  1. About hybrid rice, from the International Rice Research Institute.
  2. Hybrid rice Archived 2012-02-13 at the Wayback Machine, International Rice Research Institute
  3. FAO.org (2004). "Hybrid Rice for Food Security" (PDF). Fact Sheet. Food and Agriculture Organization of the United Nations. Retrieved 2009-10-19.
  4. The man who puts an end to hunger: Yuan Longping, "Father of Hybrid Rice". Beijing: Foreign Languages Press. 2007. ISBN 9787119051093.
  5. Hybridizing the world - The father of hybrid rice, Rice Today (Oct-Dec, 2010)
  6. Hope from hybrid rice, China Daily, 21 September 2011.
  7. Ren, Weidong (2018-04-11). "追忆高原杂交稻之父李铮友". Guangming Daily. Retrieved 2018-04-16.
  8. "李铮友同志逝世". People's Daily. 2018-04-13. Retrieved 2018-04-16.
  9. Oudhia P, Pandey N, Ganguli RN & Tripathi RS (1999) Gall midge (Orseolia oryzae) infestation in hybrid rice as affected by agronomical practices. Insect Environment 4: 123–124.
  10. Hybrid rice history, International Rice Research Institute.
  11. IRRI Technical Bulletin No.14 - Hybrid rice adoption in India: farm level impacts and challenges
  12. Our science: Hybrid rice, International Rice Research Institute.
  13. Wto. “Hybrid Rice in Asia: An Unfolding Threat.” GRAIN, https://www.grain.org/article/entries/34-hybrid-rice-in-asia-an-unfolding-threat.
  14. Progress and Issues in Development and Use of Hybrid Rice in the Tropics - S.S. Virmani, http://www.fao.org/3/Y4751E/y4751e0g.htm.
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