PHYSICALLY MAPPING QUANTITATIVE TRAITS FOR STRESS-RESISTANCE IN THE FORAGE GRASSES

Recent advances in cytogenetics of the Lolium/Festuca complex provide new opportunities for understanding and manipulating physiological mec hanisms in complex quantitative traits such as stress resistance. The complex provides a valuable reserve for research and breeding since (a ) it includes a wide range of valuable agronomic characters, (b) it ha s the capacity for intergeneric hybridization with promiscuous recombi nation, and (c) its genomes, despite their close homology, have suffic ient structural heterogeneity to allow Lolium and Festuca chromosomes to be discriminated using genomic in situ hybridization (GISH). Two al ternative procedures are used to 'dissect' stress-resistance traits in to their individual components both to determine their function and to physically map the relevant QTL(s) onto chromosome arms: (a) Festuca genes are introgressed into Lolium to improve stress resistance, (b) L olium genes are introgressed into Festuca to reduce stress resistance. Whichever approach is used, alien introgressions can be detected by G ISH and assigned to chromosome arms to create a physical map. Genes of interest may then be located more accurately following further recomb ination events which reduce the size of the relevant alien introgressi on. It has become obvious during the past years that genetic and physi cal maps are not directly comparable as chiasmata are not evenly distr ibuted along the chromosome axis. By integrating physical maps created by GISH and genetic linkage-maps, the precise site of genes on a chro mosome arm may be determined, and markers found which are tightly link ed to the genes of interest, for future use in breeding programmes.