To enhance crop production in a sustainable manner, Green Super Rice (GSR) was proposed as a new goal for rice breeding and production based on the prospect of rapid progress in rice functional genomics research. Rice scientists in China proposed the concept of GSR to breed and produce a new type of rice that requires fewer pesticides, fewer fertilizers, and reduced irrigation while exhibiting greater stress resilience without compromising grain yield and quality. GSR practices and achievements have led the way toward a paradigm shift in rice breeding and production goals from the pursuit of higher yields since the 1960s to enhanced productivity with resource-saving and environmentally friendly approaches. Inspired by the notion of GSR development and deployment, Chinese scientists have also advocated the idea of a resource-saving and environmentally friendly agricultural system or “green agriculture”.
Efforts to meet the increased food demand have had great success in keeping pace with population growth in the past several decades. However, such efforts have resulted in high-input and resource-intensive farming systems, which have serious and often negative impacts on the environment and natural resources, including land and water, thus threatening sustainable food and agricultural production.
Therefore, innovative agricultural systems are needed to protect and enhance the natural resource base while increasing productivity. Ensuring food security and sustainable development of agriculture using resource-saving and environmentally friendly technologies has become a strategic concern worldwide.
To enhance crop production in a sustainable manner, Green Super Rice (GSR) was proposed as a new goal for rice breeding and production based on the prospect of rapid progress in rice functional genomics research. In the past decade, many rice cultivars with various green traits (traits desired for resource-saving and environmentally friendly crop production, such as resistance to multiple abiotic and biotic stresses and water- and nutrient-use efficiency) have been developed. These cultivars have been planted across large areas in China and many other Asian and African countries.
Although credited as a major success in terms of enhancing crop productivity, the Green Revolution has been accompanied by excess inputs (chemical fertilizers, pesticides, water, etc.) and has had significant negative impacts on resources and the environment. These have become increasingly serious and are widely recognized as threatening to long-term sustainability.
The other major boost in rice productivity followed the development and wide adoption of hybrid rice in China and many other countries, beginning in the mid-1970s. Breeding approaches such as modifications in plant architecture and exploitation of inter-subspecies hybrid vigor between the two main rice subspecies (xian/indica and geng/japonica) have achieved some success in the development of high-yielding varieties. However, because an emphasis on high yield was the top priority, the increased food production from high-yield cultivars required even higher inputs.
To meet these challenges in the late 1990s, Chinese agricultural scientists formed a consensus around a “Second Green Revolution” with the goal of “less input, more production, and better environment” to reverse the vicious cycle generated by the Green Revolution in pursuit of high grain yields. The Second Green Revolution aimed to produce abundant, healthy, and affordable food for an ever-increasing human population with fewer resources and lower environmental costs.
In accordance with the concept of the Second Green Revolution, rice scientists in China proposed the concept of GSR to breed and produce a new type of rice that requires fewer pesticides, fewer fertilizers, and reduced irrigation while exhibiting greater stress resilience without compromising grain yield and quality.
Based on the expectation of rapid progress in rice functional genomics research, a comprehensive strategy was adopted for the development of GSR. In this project, genomics, germplasm resources, and breeding activities were integrated to breed GSR varieties with combinations of green characteristics, such as resistance to multiple diseases and insects, water savings and drought tolerance, high nutrient-use efficiency, and improved tolerance to abiotic stresses, together with high yield and superior quality. Field cultivation and green protection technologies were also developed and incorporated into the project for GSR production
In the past decade, tremendous achievements have been made in the development and adoption of GSR through the integration of conventional breeding and genomic breeding, combined with the use of improved agronomic practices, such as mechanization and simplification of crop management.
A large number of cultivars with multiple desirable genes have been developed and widely adopted in China and other countries. By the end of 2018, a total of 66 new varieties with various combinations of beneficial agronomic characteristics had been approved by variety approval committees at the national or provincial level in China. In addition, 66 varieties produced by GSR breeding efforts at IRRI have been released to rice production areas outside of China.
Many of these cultivars with diverse GSR traits (such as blast resistance, BPH resistance, drought resistance, or efficient nitrogen use) have been grown in large areas of China and other Asian and African countries. The cumulative production area of GSR cultivars exceeded 10.87 million hectares across five main rice-growing regions of China from 2014 to 2018.
The total area of demonstration and popularization of GSR varieties in African, South Asian, and Southeast Asian countries reached approximately 6.12 million hectares, making a significant contribution to rice production and food security worldwide.
As part of the GSR project, key crop management technologies for GSR varieties were developed and popularized, such as site-specific nutrient management, precise water-saving irrigation technology, and simplified and mechanized cultivation technology.
Other field management technologies, including green control of insects and diseases and environmentally friendly tools, were developed and recommended to farmers for rice production. GSR varieties combined with improved, efficient cultivation technologies can contribute to stable and high yields while reducing the application of pesticides and fertilizers by 30% and the use of irrigation water by at least 30% in irrigated rice production areas.
For example, 22 water-saving and drought-resistant rice (WDR) cultivars that can be grown in both irrigated and rain-fed ecosystems were registered in China and distributed to farmers in recent years. With superior drought tolerance, WDR varieties can be used in rain-fed environments with dry seeding and aerobic field management, just like wheat, and can also be used in irrigated rice fields like any other rice variety. Their use can reduce sowing, transplanting, and other inputs.
The excellent WDR cultivar “Hanyou 73” has been widely grown by dry-seeding on rain-fed land, producing high and stable yields. It yielded 9.3 t/ha in a demonstration field trial in Anhui province through mechanical direct seeding and required only two irrigations with a total irrigation volume of 1200 m3/ha throughout the entire growth period, resulting in >50% water savings.
GSR development and deployment have provided models for greatly improving water- and nutrient-use efficiency, achieving environmentally friendly crop production, and enhancing staple crop resources in a sustainable manner.
GSR practices and achievements have led the way toward a paradigm shift in rice breeding and production goals from the pursuit of higher yields since the 1960s to enhanced productivity with resource-saving and environmentally friendly approaches. Inspired by the notion of GSR development and deployment, Chinese scientists have also advocated the idea of a resource-saving and environmentally friendly agricultural system or “green agriculture”.
The concept of green agriculture has also made progress as the Chinese government has stressed the importance of green agricultural development in recent years. In 2017, the Ministry of Agriculture and Rural Affairs of China reformed the “National Criteria of Major Crop Variety Certification.” The revised document stressed green development and gave priority to “green and superior quality.”
In 2019, criteria and guidelines for green cultivars were officially issued for rice, wheat, maize, and soybeans, clearly pointing out that “less pesticide, less fertilizer, water savings and drought resistance, superior quality, and high yield” were the future breeding objectives and directions for major crop production in China. However, achieving the goals of sustainable crop production will still require “less input, more production, and better environment,” a coordinated effort of efficient discovery and exploitation of novel genetic diversity, development of new green crop cultivars, and innovative breeding strategies, cultivation techniques, and industrialization chains.
Recently, GSR was listed in a document (Briefing 10) prepared by the Royal Society for the United Nations Climate Conference 26 as an example of scientific solutions to the challenge of Nourishing ten billion sustainably: resilient food production in a time of climate change.
Climate change and greenhouse gas emissions have huge impacts on global food production and are causing increasingly serious concerns worldwide; food production accounts for approximately one-third of global greenhouse gas emissions from human activities. The notion and activities of GSR involve breeding new types of rice varieties by making best use of the latest technologies, leading to reduced pesticide, fertilizer, and irrigation use in rice production and thus reducing greenhouse gas emissions.
In practice, the popularization of GSR in various rice-producing regions has demonstrated that GSR varieties may contribute significantly to high yields and stable production while reducing nitrogen fertilization, pesticide use, or irrigation by as much as 30%. The GSR project has been regarded as “one of the world’s foremost scientific efforts to create a climate-resilient, high-quality crop.”
Two frontiers have emerged from the development of the GSR project, as well as the social development of China and many other countries. The first is to address the changing direction of rice production and breeding in response to rising demands of consumers and climate change. The second involves the transformation of breeding technologies brought about by the development of genomic research.
With increasing living standards, consumers and societies are paying more attention to food nutrition, requiring staple foods to provide beneficial nutrients for health in addition to calories. Crop breeding should address this demand to improve the nutritional value of food crops and promote human health. In recent years, nutritional quality as part of grain quality has become a priority in a range of rice breeding programs.
The emphasis has switched from traditional grain quality (e.g., grain appearance, milling quality, and cooking and eating quality) to micronutrients, bioactive compounds, antioxidants, and so forth. Rice is rich in diverse nutrients, including protein, unsaturated oil, and other beneficial components such as minerals, vitamins, dietary fiber, flavonoids, and polysaccharides.
These nutrients are present mainly in the pericarp, seed coat, aleurone, embryo, and endosperm. In particular, black rice is also rich in anthocyanins, which have demonstrated health-promoting effects.
However, for thousands of years, consumers have traditionally preferred the palatability of milled rice or even highly polished rice, from which ∼80% of the nutrients in the grain have been discarded as bran. Consumption of whole-grain rice, especially black rice, has been advocated in order to gain its full health benefits.
However, a major obstacle is the palatability of black rice. Whole grains of black rice varieties currently available in the marketplace are difficult to cook, and the taste of the cooked rice is quite unpleasant. With advances in genomic research, it is now feasible to breed black rice varieties with improved cooking texture and palatability. Such genetic improvements will provide the key to unlocking a huge unmined treasury of human nutrition.
The future development of green super crops with superior productivity, resilience to abiotic/biotic stresses, and high quality will require novel technologies for breeding by design based on accurate information from functional and population genomics research. Fortunately, rapid developments in functional and population genomics research on major crops, especially low-cost sequencing technology, information on genomic diversity from large-scale resequencing, and functional characterization of thousands of genes, have broadened the horizons of the genomic breeding paradigm.
For example, a genomic breeding project may now consist of the following components:
(1) designing a green super crop cultivar for a specific targeted environment, i.e., defining the breeding objectives, including yield level, lifespan, quality specifications, insect and disease resistance, stress tolerance, etc.;
(2) identifying one elite cultivar (A) that has the most traits that best fit the breeding goals;
(3) characterizing the genetic constitution of cultivar A by whole-genome sequencing and determining possible target genes/alleles for trait modification (i.e. genes/alleles missing in cultivar A according to the breeding objectives);
(4) identifying matching donor(s) that can provide the target genes/alleles with minimum genetic drag; and
(5) developing the most efficient scheme of crossing, backcrossing, and selection for precise improvement of the target traits by accurate and rapid transfer of the target genes from the donor(s) to cultivar A.
The outcome of such a process is typically a series of NILs in the cultivar A background, each containing a genomic fragment of <100 kb harboring the target gene from the donor line. The NILs may be used directly for rice production or crossed with one another to stack more target genes, depending on the breeding goal. Genome breeding as conceptualized and illustrated above provides a new paradigm for crop breeding for more efficient development of green super crop cultivars to ensure green agriculture in the not-too-distant future.
Read the study:
Yu S, Ali J, Zhou S, et al. (2022). From Green Super Rice to green agriculture: Reaping the promise of functional genomics research. Mol. Plant. 15, 9–26.
