GENETIC AND PHYSICAL CHARACTERIZATION OF THE LR1 LEAF RUST RESISTANCELOCUS IN WHEAT (TRITICUM-AESTIVUM L)

The objective of this study was to characterize the leaf rust resistan ce locus Lr1 in wheat. Restriction fragment length polymorphism (RFLP) analysis was performed on the resistant line Lr/16Thatcher and the s usceptible varieties Thatcher and Frisal, as well as on the segregatin g F-2 populations. Seventeen out of 37 RFLP probes mapping to group 5 chromosomes showed polymorphism between Lr1/6Thatcher and Frisal, whe reas 11 probes were polymorphic between the near-isogenic lines (NILs) Lr1/6Thatcher and Thatcher. Three of these probes were linked to the resistance gene in the segregating F-2 populations. One probe (pTAG62 1) showed very tight linkage to Lr1 and mapped to a single-copy region on chromosome 5D. The map location of pTAG621 at the end of the long arm of chromosome 5D was confirmed by the absence of the band in the n ulli-tetrasomic line N5DT5B of Chinese Spring and a set of deletion li nes of Chinese Spring lacking the distal part of 5DL. Twenty-seven bre eding lines containing the Lr1 resistance gene in different genetic ba ckgrounds showed the same band as Lr1/6Thatcher when hybridized with pTAG621. The RFLP marker was converted to a sequence-tagged-site marke r using polymerase chain reaction (PCR) amplification. Sequencing of t he specific fragment amplified from both NILs revealed point mutations as well as small insertion/deletion events. These were used to design primers that allowed amplification of a specific product only from th e resistant line Lr1/6Thatcher. This STS, specific for the Lr1 resist ance gene, will allow efficient selection for the disease resistance g ene in wheat breeding programmes. In addition, the identification of a D-genome-specific probe tightly linked to Lr1 should ultimately provi de the basis for positional cloning of the gene.