In recent years, the rapid development of rice breeding technology and functional genome research has prepared a large number of genes with important utilization value for rice genetics and breeding in my country, and rice breeding is moving towards a new era of design breeding. The innovative development of rice breeding has greatly enhanced my country's international leading position in the field of rice breeding, and ensured my country's food ration security. It has made great contributions to the development of my country's society and economy for "less input, more output, and environmental protection".

1 Status and progress of rice breeding in my country

1.1 The quantity of rice varieties has exploded and the quality has improved

After 2014, the state has successively launched the green channel for variety approval and the consortium test channel, and the methods of variety testing have become more diversified, and the number of tested varieties has increased rapidly. The number of rice varieties approved at the national or provincial level in 2016 was 551, 676 in 2017, and 943 in 2018, 1.40 times the number of approved varieties in 2017. Among them, the number of indica varieties increased by 77.3%, and the number of hybrid rice varieties increased by 77.3%. The number of new hybrid rice varieties has increased by 71.8%, and the proportion of two-line hybrid rice has accounted for 44.8% of the approved new varieties of hybrid rice. The quality traits of the approved varieties have been improved. Among the 268 nationally approved varieties in 2018, high-quality rice accounted for 50.0%, and among the locally approved varieties, high-quality rice accounted for 34.6%; in terms of resistance, among the nationally approved varieties, rice blast resistance The proportion of varieties is relatively high, with 38 varieties, accounting for 14.2%; 8 varieties are resistant to bacterial blight, and 2 varieties are resistant to brown planthopper; 255 varieties of locally approved rice varieties have the characteristics of resistance to rice blast, accounting for There are 71 varieties resistant to bacterial blight, 57 varieties resistant to rice false smut, 76 varieties resistant to sheath blight, and 43 varieties resistant to stripe blight.

1.2 Super rice achieves the fifth breeding goal

Since the Ministry of Agriculture and Rural Affairs organized and implemented the "China Super Rice" project in 1996, through the collaborative research of scientific and technological workers, my country has made great progress in the theoretical methods, material creation, and variety breeding of super rice. There are a large number of super high-yielding varieties. Currently, there are 132 varieties of super rice, including 35 conventional rice and 97 hybrid rice. In high-yield research and production practice, these varieties have shown super-high-yield potential. In 2016, the fifth-phase breeding yield target of 16.0 t/hm2 was achieved. It has provided scientific and technological support to increase” and ensure national food security.

1.3 Indica-Japonica hybrid rice achieves regional breakthroughs

In recent years, the utilization of heterosis between indica and japonica subspecies has developed rapidly in the middle and lower reaches of the Yangtze River, especially in the Hangjiahu region. Using the strategies of "mixing indica with japonica" and "mixing indica with japonica", the Ningbo Academy of Agricultural Sciences of Zhejiang Province and China Rice Research Institute and other units used the japonica sterile line and the indica-japonica intermediate restorer line to breed the " Indica-japonica inter-subspecies hybrid rice, such as Yongyou, Chunyou, Zheyou and Jiayou Zhongke, has shown a good momentum of development in the southern rice area. As of 2018, 38 combinations have passed the national Approved, 8 of them have been named super rice, and the representative variety Yongyou 12 has a cumulative promotion area of ​​277,000 hm2. The first generation of indica-japonica hybrid has the characteristics of vigorous vegetative growth, high biological yield, sturdy stem, strong lodging resistance, high absolute yield, and high yield potential.

1.4 Delightful progress has been made in the utilization of japonica heterosis

In my country, the breeding of japonica three-line hybrid rice started almost at the same time as indica three-line, and the three-line matching was realized in 1975. Affected by issues such as quality, seed production yield and competitive advantage, hybrid japonica rice accounts for less than 3.0% of the japonica rice planting area. In recent years, with the innovation of breeding technology, a number of japonica sterile lines with high outcrossing characteristics and good quality have been created, such as Dianyu 1A, Dianxun 1A, Liyu A, Yumi 15A, etc. Dian-type sterile lines and BT-type sterile lines such as Liao 105A, Liao 30A, Liao 02A, Liao 5216A, Liao 99A, Liao 11A, Liao 143A and L6A were bred into Dianza 31, Yunguang 12 and Yunguang 14 , Liaoyou 9906, Liao 16 You 06, Liao 73 You 62, Jingyou 558, Jingyou 106, Jingyou 165, Jinjingza 2, Jinjingza 4, Tianlongyou 619, etc. have strong resistance and good quality , a new combination of high-yield hybrid japonica rice, and began to emerge in production. In particular, the breeding of Tianlongyou 619 has made the dream of hybrid rice cultivation in cold regions a reality. The successful planting and popularization of Tianlongyou 619 not only solved the technical problems of poor quality of hybrid japonica rice and unstable seed production, but also provided a new variety for the replacement of the well-known conventional japonica rice "Daohuaxiang" in my country.

1.5 Molecular technology accelerates the precision of rice breeding

Molecular marker breeding, transgenic breeding and molecular design breeding are the three main types of molecular breeding. At present, molecular marker breeding has been widely used in the resistance and quality improvement of rice backbone parents, and major breakthroughs have also been made in rice molecular design breeding. Deng Xingwang et al. used the stably inherited recessive male sterility material to restore the pollen fertility by transferring the fertility restoration gene, and at the same time used the pollen inactivation (abortion) gene to inactivate the pollen containing the transgenic component (abortion). , and use fluorescence sorting technology to quickly separate the two types of seeds of sterile line and maintainer line, so as to propose "intelligent sterile hybrid breeding technology" or "third-generation hybrid rice technology"; China Rice Research Institute and Chinese Academy of Sciences Genetic and The Institute of Developmental Biology actively designed 28 excellent genes in the sequenced varieties Nippon Bare and 9311, using "Teqing" as the gene receptor, and after years of polymerization selection, finally obtained several excellent progeny materials, which are fully preserved. The genetic background and high-yield characteristics of "Teqing" were significantly improved, and the rice appearance quality, cooking and eating quality, taste and flavor were significantly improved, and the quality of the hybrid rice was also significantly improved. The results of this study have guiding significance for promoting the transformation of traditional rice breeding to efficient, precise and directional molecular design breeding.

1.6 Progress in improving rice with genome editing technology

Genome editing technology refers to the genetic manipulation technology that can carry out site-specific modification of DNA sequences at the genome level, which has great application value in the genetic improvement of rice. LI et al. used CRISPR/Cas9 technology to carry out site-directed modification of genes that negatively regulate rice yield, and obtained materials with significantly increased number of grains per panicle or grain density and grain length; MA et al. used CRISPR/Cas9 technology to target mutant amylose The synthase gene OsWaxy, the amylose content of the mutant decreased from 14.6% to 2.6%, thus obtaining waxy quality; Wang et al. used the rice blast-susceptible variety Kongyu 131 as the material and used CRISPR/Cas9 technology to target knockout OsERF922, the obtained T2 homozygous mutant line had significantly improved resistance to M. oryzae at both the seedling and tillering stages compared to the wild type. Shimatani et al. used the CRISPR/Cas9-based Target-AID method to mutate the 96th propyl amino acid of the rice ALS coding region to valine, and obtained a rice mutant resistant to sulfonylurea herbicides. LI et al. used CRISPR/Cas9 technology to target and edit the endogenous gene csa (Carbon Starved Anther) of japonica rice variety Kongyu 131, and obtained a japonica photosensitive male sterile line. ZHOU et al. used CRISPR/Cas9 technology to specifically edit the rice thermosensitive male sterility gene TMS5, and created a batch of thermosensitive male sterility lines. In 2019, WANG and KHANDAY established an apomixis system in hybrid rice at almost the same time. Through apomixis, the genotype of the hybrid was fixed, and the cloned seeds of the hybrid rice were obtained, which completely subverted the traditional breeding and seed production procedures and seized the world agricultural science. Especially the strategic commanding heights of future breeding models.

2 Comparison of the development of rice breeding technology at home and abroad

The domestic hybrid rice breeding technology, especially the three-line and two-line hybrid rice breeding technology, is ahead of foreign countries, and the promotion area of ​​hybrid rice is large. At present, more than 40 countries in Asia, Africa and the Americas have introduced, researched and promoted hybrid rice. The overseas promotion area of ​​hybrid rice exceeds 3.5 million hm2, including about 2 million hm2 in India, about 670,000 hm2 in Vietnam, and about 54 million hm2 in the United States. 10,000 hm2, about 340,000 hm2 in the Philippines. From the perspective of the proportion of hybrid rice planting area, China and the United States accounted for 50%, Indonesia accounted for 7%, and ASEAN and South America accounted for 4%.

my country still leads the world in super-high-yield breeding. In 2016, among the 10 countries with the largest rice planting area in the world, my country's yield per unit was the highest, reaching 462.5 kg/667 m2, which was 327.4 kg/667 m2 higher than the lowest, Nigeria. With the rapid development of my country's economy and the acceleration of urbanization, my country's agriculture will still face the contradiction between the rigid growth of food demand and the shortage of arable land, water and other resources, the contradiction between the balance of food supply and demand and the structural shortage, and the rising cost of agricultural production. Contradiction with declining economic efficiency. Therefore, continuously improving the per unit yield and total yield of rice is still the main direction of our breeding. Developed countries focus on yield in terms of rice breeding goals, but also pay attention to the research on habitat and non-habitat stress, and strengthen the mining of insect resistance and stress tolerance genes and their breeding and utilization.

For rice, high yield often brings problems of poor quality and low resistance to diseases and insect pests. This situation has become a bottleneck for improving the competitiveness of my country's rice industry. In terms of quality breeding, China often pays attention to the comprehensive coordination of the "four characteristics" of yield, quality, resistance and adaptability, while developed countries pay more attention to the physical and chemical quality and eating quality of rice. In the research and industrialization of functional rice, my country has just started, and developed countries are in the lead. For example, Japan has developed low globulin rice, hay fever desensitized rice, diabetes improvement rice, serum cholesterol alleviation rice, asthma desensitization rice, Alzheimer vaccine rice, coenzyme Q10 fortified rice, and mineral fortified rice for specific disease groups. , high-amino-acid rice, high-vitamin rice, etc.; India has developed an improved variant of the rice variety ISM suitable for diabetics. In addition to its high yield, resistance to bacterial blight and other excellent traits, the glycemic index (GI) of this variant is only is 50.99.

3. Development trend and countermeasures of rice breeding technology in my country

3.1 Development Trend of Rice Genetics and Breeding in my country

3.1.1 High yield is still the main direction of rice breeding in the future

According to forecast analysis, my country's total population will increase from the current 1.340 billion to 1.428 billion in 2020, and the average annual population growth rate in the next 20 years will be maintained at about 0.50%, that is, the annual net population increase will exceed 5 million [32]. According to the standard of per capita consumption of 146.12 kg of rice in 2010, 730,000 tons of rice need to be added every year. In contrast, the sown area of ​​rice in my country has dropped from 34 million hm2 in 1978 to 30 million hm2 in 2018, with an average annual decline rate of 0.28%. In order to meet the growing population's demand for food, under the condition that the total sown area remains unchanged, increasing the unit yield will still be the main direction of rice breeding in my country in the future.

3.1.2 Hybrid rice breeding needs to be further improved

After more than 40 years of development, my country's hybrid rice has made significant breakthroughs in terms of yield, quality and resistance. Taking the hybrid rice combination that has passed the national examination in southern my country as an example, compared with the combination approved 20 years ago, the yield and gel consistency have increased by 9.40% and 5.18%, respectively, and the chalky grain rate, chalkiness, amylose The content, bacterial blight resistance grade and rice blast resistance grade decreased by 56.65%, 65.83%, 20.33%, 12.43% and 22.42%, respectively. However, the above-mentioned changing trends are inconsistent in various rice regions in my country. For example, the improvement process of agronomic traits of early indica varieties lags behind other types of varieties.

According to the existing sequence information of genes regulating important agronomic traits in rice and the sequencing analysis results of hybrid rice main planting combinations, excellent alleles have appeared in various types of rice varieties in my country to a certain extent, but their distribution is unbalanced. Taking the rice yield/quality genes GS3, GW5, Wx, Alk and the resistance genes Pi33 and Pib as examples, the utilization rates of the superior allelic variation of the above six gene loci in the main hybrid rice varieties in my country are 91.95%, 91. 94.25%, 71.84%, 44.83%, 32.77% and 28.25%, an increase of 28.49%, 13.87%, 32.61%, 21.37%, -9.66% and 8.55% respectively compared with 20 years ago. It shows that the excellent breeding parents have been used more and more in rice breeding in my country, and it also means that the overall utilization rate of these excellent alleles in my country's main hybrid rice resources still has great potential for development.

3.1.3 The creation of breeding materials will become a breakthrough point in rice breeding

According to previous reports, in addition to the emerging indica-japonica hybrid rice whose heterozygosity can reach 37.00%, the average heterozygosity of the current hybrid rice combinations in my country is only 21.83%, which is decreasing year by year; the current rice varieties still have resource-consuming types There are many varieties, few resource-saving varieties, many high-yielding susceptible varieties, few stable-yielding and disease-resistant varieties, etc., rice production is still very dependent on the input of water, fertilizer, medicine and other resource consumables, and there are major breakthroughs in high-yield and high-quality New varieties that are green and suitable for mechanization and light simplification need to be developed; the cultivation of rice varieties that meet the needs of special populations needs to be paid attention to, such as selenium-rich rice varieties and high-resistant starch varieties suitable for diabetic patients.

3.1.4 Breeding technology still needs to be improved

The combination of basic research and applied research still needs to be strengthened. On the one hand, it is necessary to use genome breeding technology and gene editing technology to accelerate the transformation of rice functional genome research results into breeding applications; New quality sources, introduce excellent exogenous genes to transform existing sterile lines and restorer lines, and use modern science and technology such as omics technology, information technology, and biotechnology to accelerate the precision, data, and intelligent transformation of rice breeding. Development, as well as exploring the use of apomictic characteristics to fix heterosis to solve the difficulties in the creation of rice breeding materials in the new era, and make a revolutionary and subversive breakthrough in breeding technology.

3.2 Countermeasures for the development of rice breeding in my country

3.2.1 Improve the new generation of rice breeding technology

In response to the strategic needs of rice industry development in the new era, strengthen basic research on rice genetics and breeding, innovate breeding technologies such as genome-wide selection, gene editing, induced mutation, and utilization of heterosis, and use gene knockout, deletion, single-base editing, and large DNA fragments. Recombination mutation is the starting point to innovate and optimize rice gene editing technology; take gene stacking as a breakthrough to improve multi-trait complex transgenic technology; through biotechnology