What Is Hybrid Rice? Understanding the Definition and Characteristics in One Article

With the application and promotion of hybrid rice, the yield per unit area has been increased and the amount of seed used has been reduced. So what is hybrid rice?

1. What is hybrid rice?

Hybrid rice refers to the selection of two rice varieties that differ to a certain extent genetically and whose superior traits can complement each other, crossing them to produce a first-generation hybrid with heterosis for production use; this is hybrid rice. Heterosis is a common phenomenon in the biological world, and using heterosis to improve crop yield and quality is one of the major achievements of modern agricultural science. The world's first successful rice hybridization was completed by the American Henry Beachell in 1963 in Indonesia, for which he was awarded the 1996 World Food Prize.

1. Research on two-line hybrid rice

Compared with three-line hybrid rice, the advantages of two-line hybrid rice are free combination of parents, simplified breeding procedures, shortened breeding cycles, and diversified male sterile lines; the disadvantages are that the multiplication of male sterile lines and hybrid seed production are limited by time and space conditions. After research on two-line hybrid rice was included in the national “863” program in 1987 and Yuan Longping published “Strategic Assumptions for Hybrid Rice Breeding,” two-line hybrid rice breeding unfolded widely across the country. In 1988, the first two-line japonica hybrid rice combination to enter productive experiments was N5047S/R9-1. By 2000, only 27 two-line hybrid rice varieties had passed provincial and prefecture-level approval nationwide, with a cumulative promotion area of about 3 million hectares, making it a period of relatively slow development. After 2001, when 4 two-line hybrid rice varieties represented by Liangyoupeijiu passed national approval, two-line hybrid rice entered a period of rapid development. By 2015, 135 two-line hybrid rice varieties had passed national approval and 816 (instances) of two-line hybrid rice varieties had passed provincial approval (http://www.ricedata.cn/variety/). In 1996, the promotion area was 180,500 hectares, accounting for 0.92% of the hybrid rice planting area; by 2013, the promotion area had grown to 5,440,400 hectares, accounting for 33.59% of the hybrid rice planting area, and over 18 years the two-line hybrid rice area expanded 30-fold. Among these, the combination with the largest promotion area was Liangyoupeijiu (Pei'ai 64S/9311), with a cumulative promotion area of more than 8 million hectares. At present, all 20 rice-growing provinces and cities nationwide have two-line hybrid rice cultivation, mainly indica-type two-line hybrid rice. The three provinces with annual promotion areas exceeding 1 million hectares are Hunan, Hubei, and Anhui, among which in Anhui and Hubei the two-line hybrid rice area has already surpassed the three-line hybrid rice area.

2. Hybrid rice cultivation techniques

1. Land preparation

In production, land must be finely prepared strictly according to requirements, so that the bed surface is level and free of weeds, drainage and irrigation are smooth, and no water accumulates. A ditch 0.6 m wide and 0.1 m deep should be dug at a bed width of 4-6 m.

2. Sowing early at the right time

Reasonably arranging the sowing period is a key measure to ensure full stands and safe full heading in direct-seeded rice cultivation.

3. Seed selection

Selecting high-yield, disease-resistant, high-quality improved varieties can increase yield and improve economic returns. Doing a good job of seed disinfection and pregermination can reduce the occurrence of pests and diseases.

4. Seed soaking

Generally, after soaking seeds for 12-18 h, sowing directly without pregermination and raising seedlings in moist conditions is preferable.

5. Pregermination

During pregermination, suitable temperature, appropriate moisture, and timely ventilation should be maintained. The most suitable temperature for rice seed germination is 30-35°C; when it exceeds 45°C, it will cause “seed burning,” and sowing can be done after more than 80% of the seeds have broken their hulls.

6. Thin and even sowing

Direct-seeded cultivation is the practice of sowing seeds directly into the field. The sowing rate is 37.5 kg/hm2 for conventional rice seed and 18.75 kg/hm2 for hybrid rice seed, generally increasing the seed rate by 15%-20% compared with normal seedling raising. Sowing should be uniform, and after sowing the sprouts should be buried; a wooden board can be used to press lightly so that the germinated grains enter the soil, while also taking precautions against bird and rodent damage.

Hybrid rice direct-seeding cultivation technology is a simplified cultivation method that omits the traditional rice cultivation seedling-raising process and directly sows soaked and pregerminated rice seeds into the field, managing them so they grow into seedlings, tiller, and mature.