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International Maize (international + maize)
Selected AbstractsOxygen isotope enrichment (,18O) reflects yield potential and drought resistance in maizePLANT CELL & ENVIRONMENT, Issue 11 2009LLORENĒ CABRERA-BOSQUET ABSTRACT Measurement of stable isotopes in plant dry matter is a useful phenotypic tool for speeding up breeding advance in C3 crops exposed to different water regimes. However, the situation in C4 crops is far from resolved, since their photosynthetic metabolism precludes (at least in maize) the use of carbon isotope discrimination. This paper investigates the use of oxygen isotope enrichment (,18O) as a new secondary trait for yield potential and drought resistance in maize (Zea mays L). A set of tropical maize hybrids developed by the International Maize and Wheat Improvement Center was grown under three contrasting water regimes in field conditions. Water regimes clearly affected plant growth and yield. In accordance with the current theory, a decrease in water input was translated into large decreases in stomatal conductance and increases in leaf temperature together with concomitant 18O enrichment of plant matter (leaves and kernels). In addition, kernel ,18O correlated negatively with grain yield under well-watered and intermediate water stress conditions, while it correlated positively under severe water stress conditions. Therefore, genotypes showing lower kernel ,18O under well-watered and intermediate water stress had higher yields in these environments, while the opposite trend was found under severe water stress conditions. This illustrates the usefulness of ,18O for selecting the genotypes best suited to differing water conditions. [source] Phenotyping approaches for physiological breeding and gene discovery in wheatANNALS OF APPLIED BIOLOGY, Issue 3 2009M. Reynolds Abstract Conceptual models of drought-adaptive traits have been used in breeding to accumulate complementary physiological traits (PT) in selected progeny, resulting in distribution of advanced lines to rain-fed environments worldwide by the International Maize and Wheat Improvement Center (CIMMYT). Key steps in PT breeding at CIMMYT include characterisation of crossing block lines for stress adaptive mechanisms, strategic crossing among parents that encompass as many target traits as possible and early generation selection (EGS) of bulks for canopy temperature (CT). The approach has been successful using both elite × elite crosses as well as three way crosses involving stress adapted landraces. Other EGS techniques that are amenable to high throughput include measurement of spectral reflectance indices and stomatal aperture-related traits. Their genetic- and cost-effectiveness are supported by realisation of genetic yield gains in response to trait selection, and by economic analysis, respectively. Continual reselection within restricted gene pools is likely to lead to diminishing returns, however, exotic parents can be used to introduce new allelic diversity. Examples include landraces from the primary gene pool, and products of inter-specific hybridisation with the secondary gene pool consisting of closely related wheat genomes. Both approaches have been successful in introducing stress-adaptive traits. The main problem with knowing which genetic resource to use in wide-crossing is the uncertainty with which phenotypic expression can be extrapolated from one genome/genepool to another because of their unimproved or undomesticated genetic backgrounds. Nonetheless, their PT expression can be measured and used as a basis for investing in crossing or wide crossing. Discovering the genetic basis of PT is highly complex because putative QTLs may interact with environment and genetic background, including genes of major effect. Detection of QTLs was improved in mapping populations where flowering time was controlled, while new mapping populations have been designed by screening potential parents that do not contrast in the Rht, Ppd and Vrn alleles. Association genetics mapping is another approach that can be employed for gene discovery using exclusively agronomically improved material, thereby minimising the probability of identifying yield QTLs whose alleles have been already improved by conventional breeding. [source] Adapting wheat cultivars to resource conserving farming practices and human nutritional needsANNALS OF APPLIED BIOLOGY, Issue 4 2005R M TRETHOWAN Summary As farmers increasingly adopt resource conserving farming practices, there is a need for wheat cultivars that better adapt to the changing environment and the nutritional needs of people, particularly those living in developing countries. Improved adaptation to zero and minimum tillage, better water use efficiency, improved root health, durable resistance to foliar diseases and enhanced nutritional value of the grain are key selection criteria for plant breeders. Significant responses to selection for these constraints have been achieved at the International Maize and Wheat Improvement Center (CIMMYT), by selecting segregating populations and advanced lines in carefully managed tillage, moisture deficit and heat stressed environments, that correlate with key spring wheat growing environments globally. Root health has been improved through a combination of marker assisted selection and disease bioassays, and the nutritional value of wheat grain has been enhanced using genetic variation for high Fe and Zn grain content found among tetraploid wheat ancestral species. [source] Beyond semi-dwarf wheat yield increases: impacts on the Australian wheat industry of on-going spillovers from the International Maize and Wheat Improvement CenterAUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2007John P. Brennan Wheat genetic materials developed from research at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico for developing countries have provided spillover benefits to Australia. Varieties developed from those genetic materials have resulted in yield increases in Australia. While the initial impact came through the introduction of higher-yielding semi-dwarf wheat crops, those impacts have continued in the post-semidwarf period. CIMMYT's success in developing countries has also reduced the world price for wheat. While the lower prices affect returns in Australia, the increased yields in Australia from the CIMMYT spillovers from both the semi-dwarfs and the post-semidwarf phases have provided benefits to Australia averaging A$30 million per year. [source] | ||||||||||