DIRECT CLASSIFICATION AND SELECTION OF SUPERIOR ALLELES FOR CROP IMPROVEMENT

The use of conventional breeding methods has resulted in consistent cr op improvement within the cultivated gene pool by producing genotypes with new combinations of alleles that produce better phenotypes than e ither of the parents (transgressive segregation). Biotechnology has pr ovided new methods to generate, identify, characterize, and manipulate genetic variation. Among these methods, marker assisted selection (MA S) with DNA markers has been applied in plant improvement programs. Ho wever, MAS is limited by the effort required to generate information a bout map location and breeding value of genes controlling important tr aits. Comparative genetic analysis across the domesticated grasses fac ilitates the identification and localization of gene sequences control ling specific traits of interest. The emerging databases of gene seque nces will allow directed discovery of genes in higher plants and class ification of alleles present within breeding germplasm. Identification of the genes controlling a trait and knowledge of their DNA sequence would facilitate classification of variation in the germplasm pool bas ed on gene fingerprinting or characterization of variation in key DNA sequences. Classification of sequence variants at a targeted locus wou ld substantially reduce the amount of work required to determine their relative breeding value and lead to the identification of superior al leles. Combining direct allele selection (DAS) with conventional selec tion, would allow more rapid and precise improvement of populations an d breeding lines. Limitations of current technology can be minimized b y transfer of genetic information across species, identification of hi ghly variable genes, and focusing on the most important genes and trai ts for the species of interest.