Hybrid rice is a type of rice that has been bred from two very different parents.It requires specialized seed production to keep the seed pure. To understand hybrid rice it first helps to understand what inbred rice is.
What is inbred rice?
Most varieties of rice grown by farmers around the world are "inbred" rice varieties. This means that the seed and subsequent crops from succeeding generations produced by the inbred variety will have the same genetic makeup as the parent crop.
Rice is a self-pollinating plant. Each rice flower contains both male and female parts, which allow each flower to pollinate itself without the need for other flowers, or other rice plants. Self-pollination is a natural and normal process. Farmers can save seed from their crop of inbred rice and replant it again knowing it will have the same properties as the parent crop it came from, provided cross-pollination with other varieties is avoided.
Cross pollination of rice in a farmer’s field can occur, but usually at relatively low rates depending on the layout of the field and the local environment. Rice pollen is short-lived (15 minutes) and there are no known insect pollinators – which reduces the means by which cross-pollination can naturally occur.
When breeding a new inbred rice variety scientists first cross two or more different varieties, then select the best offspring from subsequent generations of inbreeding until they get an inbred with all the characteristics they are breeding for. Most of the new rice varieties developed by IRRI are inbred rice varieties.
What is hybrid rice?
A hybrid rice is a variety of rice that has been bred from two very different parents. The seed from the first cross of the two different parents is the hybrid variety. This is unlike inbred rice where the seed of a subsequent generation (usually after many inbreeding crosses) is the variety.
Hybrid rice breeding first requires identifying two optimal parents that when crossed together produce a rice hybrid with desirable attributes including higher yield. Because rice is self-pollinating, crossing the two different parents is difficult and requires one of the parents to have sterile pollen (or male sterility) so it can accept the pollen from another variety. Male sterility can be a genetically controlled trait that can be incorporated into a parent line of rice for breeding purposes.
The male-sterile parent (the one that cannot produce its own pollen) can then be pollinated by the other parent (which is fully fertile), creating the cross that results in a hybrid. The seed born from the male-sterile parent are the seed of the new hybrid rice variety.
Given the technical challenges of producing hybrid rice seed, hybrid rice seed production is usually only done by commercial seed producers who have the necessary knowledge, skills, and capacity to manage a very specialized field configuration and management to facilitate the cross pollination of the two parents and segregation of the hybrid rice seed to ensure its purity.
As with other hybrid plants and animals, hybrid rice has both greater vigor and higher yield than either parent variety – this is commonly called "hybrid vigor". When grown under the same conditions as comparable high-yielding inbred rice varieties, commercial hybrid rice can generate up to 30% higher yields.
China's Professor Yuan Longping is touted as the "Father of Hybrid Rice". In the 1960s and '70s his work led to the development of rice with genetically inherited male sterility. This meant that self-pollination was stopped in this rice, allowing it to be pollinated by a different parent, which facilitated cross-pollination. This technique is now widely used by rice breeders around the world to develop hybrid rice.
In 1974, the first three hybrid rice varieties were released in China, and by 1976 large-scale commercialization of hybrid rice was established.
Although the first generation of hybrid rice varieties released had higher yields, they also tended to have inferior grain quality and inadequate disease and insect resistance. Rice scientists have since overcome these problems and the current generation of hybrid rice has excellent grain quality and better resistance to pests and diseases – equivalent to or better than their inbred counterparts.
Hybrid rice has been widely adopted in China - the world's biggest producer of rice - with around 56% of the rice planted in China made up of hybrid rice. Hybrid rice is credited with contributing to China’s high rice yields that, in 2009, averaged around 6.6 tons per hectare – well above the world average of 4.2 tons per hectare in the same year.
In 2011, hybrid rice was also grown by farmers in Indonesia, Vietnam, Myanmar, Bangladesh, India, Sri Lanka, Brazil, the United States, and the Philippines.
Wider-scale adoption of hybrid rice has been limited, however, because hybrid rice production relies on commercial and sophisticated seed production systems, which are not well established across Asia – the heart of global rice production. The rice science sector and seed industry are addressing these related issues to help ensure farmers can access affordable and high-quality and high-yielding hybrid rice seed tailored to tackle difficult growing environments.
IRRI has been involved in hybrid rice research since 1979. Our research into hybrid rice now focuses on producing hybrid rice with consistently high-yield heterosis (hybrid vigor), good grain quality, tolerance to key environmental stresses, multiple resistances to insect pests and diseases, and high seed production yield.
In 2008, IRRI established the Hybrid Rice Development Consortium to collaborate more closely with our partners to undertake a range of research to support the development of new hybrid rice varieties.
Dr. Achim Dobermann, IRRI's Deputy Director for Research, announces the establishment of an international Hybrid Rice Development Consortium (HRDC) to strengthen public-private sector partnerships in the hybrid rice sector.