China was the first country to use cytoplasmic male sterility to develop hybrid rice for commercial use in 1973. In 1986 more than 8 million hectares of hybrid rice were planted in China, which is one fourth of the total rice area and produces one third of the total rice in the country. Hybrids usually out yield the leading commercial varieties by -20-30%, giving an average yield advantage of 1 to 1. 5 t/ha, because of their better morphological traits, higher physiological efficiency, better resistance to major diseases and insects, and wide adaptability to various agro-ecological stresses. IMPROVEMENT OF HYBRID RICE A. Mutation techniques Almost all of the cultivated F1 rice hybrids in China are developed from cytoplasmic male sterile and restorer lines. According to surveys made in recent years, more than 30 sources of cytoplasmic male sterility in rice can be identified, among which only six are being commercially used (Table 1). Wild rice with aborted pollen (WA) cytosterility system is the most popular one in use to develop male sterile lines (MS line) in China. The main technique available for developing stable MS lines is sUbstitution backcrossing of the genome of one species into alien cytoplasm of another. Sufficient backcrosses are required to eliminate all nuclear genes derived from the cytoplasm donor species. A number of studies have shown that using interspecies crosses, such as the cross of wild rice (Q. perennis, Q. sativa, f.

There are clearly many directions in which the further development of the GUS gene fusion system can progress. Some of these have been outlined above, but others can be imagined. There are no reasons to limit our conceptions of the use of GUS gene fusions to analysis and manipulation of single genes. We can envision numerous marked genes - perhaps with several new fusion systems - giving valuable information about gene interaction, or population structure. The study of plan- pathogen and plant symbiont interactions can progress rapidly with simple quantitative markers for genes and individuals. We can imagine ways of using gene fusions to report on crop physiology or other complex phenotypes, thereby enhancing the accuracy and speed of screening. Introduction of the biosynthetic pathway for glucuronide detoxification by expressing genes for the UDP-glucuronyl transferases in plants may result in novel mechanisms for plants to deal with xenobiotics such as insecticides or herbicides. Synthesis of substrates, which until now has been performed chemicall- resulting in expensive compounds - can be done biosynthetically. This should make the system not only the most powerful gene fusion system for agriculture, but also the most accessible.

Genetic variability is an important parameter for plant breeders in any con ventional crop improvement programme. Very often the desired variation is un available in the right combination, or simply does not exist at all. However, plant breeders have successfully recombined the desired genes from cultivated crop gerrnplasm and related wild species by sexual hybridization, and have been able to develop new cultivars with desirable agronomie traits, such as high yield, disease, pest, and drought resistance. So far, conventional breeding methods have managed to feed the world's ever-growing population. Continued population growth, no further scope of expanding arable land, soil degradation, environ mental pollution and global warrning are causes of concern to plant biologists and planners. Plant breeders are under continuous pressure to improve and develop new cultivars for sustainable food production. However, it takes several years to develop a new cultivar. Therefore, they have to look for new technologies, which could be combined with conventional methods to create more genetic variability, and reduce the time in developing new cultivars, with early-maturity, and improved yield. The first report on induced mutation of a gene by HJ. Muller in 1927 was a major mi1estone in enhancing variation, and also indicated the potential applica tions of mutagenesis in plant improvement. Radiation sources, such as X-rays, gamma rays and fast neutrons, and chemical mutagens (e. g. , ethyl methane sulphonate) have been widely used to induce mutations.

During the last thirty years, most increases in agricultural production were achieved through high input agrieulture in areas with fertile soils and sufficient water. Intensive methods of production with high levels of nitrogen fertilizer and pesticides were often accompanied by environmental degradation and in some instances by pollution of the food supply. However, rapid population growth has also led to increasing use of marginal lands, where adverse soil and climatic eonditions are serious constraints to food production. These areas are even more sensitive to ecological destabilization. Environmentally sound systems of food production and land use are essential for meeting the food security needs of developing countries. To do this, greater genetic variability is needed within the best crop genotypes available for the areas in need coupled with better management praetices and crop rotations. These requirements can only be realized if suitable crop varieties are bred. These should be varieties with a much shorter growing period, suitable for rotation, increased tolerance or resistance to diseases and pests as weil as to drought and salinity and other adverse soil and climatic conditions.

Genetic and Genomic Resources For Cereals Improvement is the first book to bring together the latest available genetic resources and genomics to facilitate the identification of specific germplasm, trait mapping, and allele mining that are needed to more effectively develop biotic and abiotic-stress-resistant grains. As grain cereals, including rice, wheat, maize, barley, sorghum, and millets constitute the bulk of global diets, both of vegetarian and non-vegetarian, there is a greater need for further genetic improvement, breeding, and plant genetic resources to secure the future food supply. This book is an invaluable resource for researchers, crop biologists, and students working with crop development and the changes in environmental climate that have had significant impact on crop production. It includes the latest information on tactics that ensure that environmentally robust genes and crops resilient to climate change are identified and preserved. - Provides a single-volume resource on the global research work on grain cereals genetics and genomics - Presents information for effectively managing and utilizing the genetic resources of this core food supply source - Includes coverage of rice, wheat, maize, barley, sorghum, and pearl, finger and foxtail millets

Plant Breeding Reviews is an ongoing series presenting state-of-the art review articles on research in plant genetics, especially the breeding of commercially important crops. Articles perform the valuable function of collecting, comparing, and contrasting the primary journal literature in order to form an overview of the topic. This detailed analysis bridges the gap between the specialized researcher and the broader community of plant scientists.

Since the beginning of agricultural production, there has been a continuous effort to grow more and better quality food to feed ever increasing popula tions. Both improved cultural practices and improved crop plants have al lowed us to divert more human resources to non-agricultural activities while still increasing agricultural production. Malthusian population predictions continue to alarm agricultural researchers, especially plant breeders, to seek new technologies that will continue to allow us to produce more and better food by fewer people on less land. Both improvement of existing cultivars and development of new high-yielding cultivars are common goals for breeders of all crops. In vitro haploid production is among the new technologies that show great promise toward the goal of increasing crop yields by making similar germplasm available for many crops that was used to implement one of the greatest plant breeding success stories of this century, i. e. , the development of hybrid maize by crosses of inbred lines. One of the main applications of anther culture has been to produce diploid homozygous pure lines in a single generation, thus saving many generations of backcrossing to reach homozygosity by traditional means or in crops where self-pollination is not possible. Because doubled haploids are equivalent to inbred lines, their value has been appreciated by plant breeders for decades. The search for natural haploids and methods to induce them has been ongoing since the beginning of the 20th century.