Product Line 2.4. Improved rice varieties for intensive production systems
Asian urban centers have the majority of the world’s urban poor and, within the next 25 years, nearly 55% of the population of Asia will be located in these areas. Both the urban and rural poor require food at affordable prices and this must come from increased productivity in intensive rice systems, which account for 75% of total rice production. Similarly, Africa’s intensive irrigation schemes and their expansion are expected to contribute greatly to enhancing rice production in Africa. Varieties that do well in Asian irrigation schemes are expected to also perform well in Africa. For example, the well-known Sahel108 variety selected by AfricaRice and now widely grown in the Senegal River Valley is originally an IRRI variety. Rice is the leading food staple in Latin America and the Caribbean (LAC), and demand for rice is growing. During 1990-2004, rice yield in LAC expanded annually at 3.5%. LAC has unique pests and diseases, as well as distinct grain types and cropping systems. Eco-efficient rice production systems, with high productivity and low impact on the environment, are critical for the future. However, considerable opportunities to increase rice production exist given LAC’s abundant land and water resources.
Yield potential has not been increased substantially in the newer varieties released for irrigated conditions. An improved understanding of the genetic basis and physiological mechanisms of yield potential, pest resistance, and grain quality will allow the development of elite inbred germplasm with higher yield potential, multiple resistance to insects and diseases, and superior grain quality. Increasing water scarcity threatens agriculture and livelihoods, and this will be pronounced in many areas, thus requiring rice cultivars with better adaptation to aerobic conditions. Similarly, labor shortage would require the development of varieties specifically suited to mechanized direct seeding and other evolving conservation agriculture systems.
2.4.1. New generation of elite inbreds with increased yield potential
Higher-yielding varieties will be developed by focusing on key physiological plant traits and genes expected to increase yield potential, as well as by a more systematic selection for yield in early generations and in multi-environment yield trials. An improved understanding of the genetic basis and physiological mechanisms of yield potential will allow the development of elite inbred germplasm with about 10% higher yield potential and other important traits. Improvements in yield potential of inbreds will also contribute to increasing the yield potential of hybrids.
2.4.2. High-yielding varieties for irrigated systems in Asia
Conventional transplanted systems in Asia represent the largest areas of rice cultivation. Although high-yielding varieties are grown in these areas, continual progress is necessary to incorporate disease and insect resistance and improved grain quality characters. Farmers in these areas are expected to rapidly adopt new varieties that are superior to the older varieties still in cultivation. New approaches for increasing the yield potential (Product 2.4.1.) and marker-assisted breeding will be employed to develop the next generation of rice varieties for irrigated environments in Asia, combining high yield with superior grain quality and multiple resistances to diseases and insects.
2.4.3. High-yielding varieties for irrigated systems in Africa
Irrigated rice represents about 15% of the total area under rice in Africa, but this percentage is expected to increase rapidly. Irrigated rice yields in Africa are often comparable to yields obtained in Asia, but there is need for improved, high-yielding varieties, resistant to major biotic and abiotic stresses. New approaches for increasing the yield potential (Product 2.4.1.), crossing with locally adapted germplasm as well as marker-assisted breeding will be employed to develop the next generation of rice varieties for irrigated environments in Africa, combining high yield with superior grain quality and multiple resistances to diseases and insects. New irrigated rice varieties are also expected to do well in the more favorable rainfed lowland areas.
2.4.4. High-yielding varieties for irrigated systems in Latin America
Recent technological development of the LAC rice sector has had a big impact on rice yields and total production, but yield potential has not been increased substantially in the newer varieties released for irrigated conditions. Likewise, biotic stresses are a major constraint in the irrigated environments. New approaches for increasing the yield potential (Product 2.4.1.) and marker-assisted breeding will be employed to develop the next generation of rice varieties for irrigated environments in Latin America and the Caribbean, combining high yield with superior grain quality and multiple resistances to diseases and insects.
2.4.5. Rice varieties for dry seeding in aerobic rice and conservation agriculture systems
Water shortage is becoming an increasing problem in traditionally irrigated areas because of depleting groundwater resources and competing uses from other sectors. Likewise, particularly in systems such as rice-wheat, rice-maize, or rice-pulses, frequent tillage and removal of residues may lead to a decline in soil fertility and unsustainable production. Resource-conserving technologies, particularly water-saving irrigation, reduced or no tillage, and retention of residues, are required to re-vitalize yield growth, improve production efficiency, and reduce the negative impact on natural resources. However, cultivating rice under such conditions requires new genotypes adapted to dry direct seeding, that is, varieties that have early vegetative vigor, are competitive with weeds, have strong root systems, and are also resistant to lodging, root pathogens, and nematodes. Herbicide resistance may also be a useful characteristic. Genetic diversity exists for these traits, and the best donors will be crossed with high-yielding varieties to develop improved varieties for these systems. A key strategy is to select for the new traits required from early stages in the breeding cycle, under the target environments, particularly in South Asia and some areas in Latin America.
2.4.6. Improved rice varieties for temperate rice environments
Temperate japonica varieties predominate in the temperate regions of Asia, Africa and Latin America. While yields are generally high in these areas, the cultivars must be further improved for yield potential and resistance to insects and diseases as well as abiotic stress tolerance, (especially cold). High grain quality is a crucial requirement. Indica including aus type and tropical japonica rice varieties are good donors for many desirable traits, but resulting progeny often suffer from spikelet sterility, poor quality and other undesirable characteristics. New strategies will be developed to eliminate linkage drag and incorporate desirable traits into temperate japonica cultivars.
The next users are rice breeders working in GRiSP, the private sector, and NARES. Intermediate users are seed producers and distributors, including the public sector, private companies, and NGOs, and final users are farmers. It is assumed that there will be assured funding from donors and national governments to produce and deliver the required amount of seed to farmers. Germplasm sources should be available from theme 1, and management practices for intensive systems will be developed in theme 3, requiring close linkage. Seed production and dissemination will be handled by linkage with theme 6. Linkage with nationally and internationally funded development projects will facilitate the delivery of improved varieties to farmers. Theme 5 will provide feedback to breeding programs on target environments, market segments, and consumer and farmer preferences. FLAR will be a key player for impact in Latin America.
At present, the mainstream breeding programs of IRRI, AfricaRice, and CIAT largely depend on unrestricted funds, which have been dwindling during the past 20 years. This has been one of the major reasons for why progress in varietal improvement has been slower than expected. Likewise, efforts to increase the yield potential of irrigated rice have suffered from a lack of funding at levels required for making substantial breakthroughs through advanced physiology and breeding research. Partial restricted funding is provided by BMGF/USAID-CSISA, the Japan Rice Breeding project, and BMGF-STRASA, MAFF-IRRI, Philippines-IRRI, ICAR-IRRI, and RDA-IRRI projects. Research at CIAT is currently funded by CIDA, Agrosalud, the Ministry of Agriculture and Rural Development of Colombia, FEDEARROZ, FLAR, Peru, and other projects from GCP, and CIAT Core. Many national partners are contributing through in-kind support and research personnel. Large amounts of additional resources are urgently needed, particularly to support more work on breaking the yield barrier. National partners are contributing through in-kind support and research personnel.