PHYSICAL MAPPING OF THE LIGULELESS LINKAGE GROUP IN SORGHUM-BICOLOR USING RICE RFLP-SELECTED SORGHUM BACS

Physical mapping of BACs bu fluorescent in situ hybridization (FISH) w as used to analyze the liguleless (Ig-1) linkage group in sorghum and compare it to the conserved region in rice and maize. Six liguleless-a ssociated rice restriction fragment length polymorphism (RFLP) markers were used to select 16 homeologous sorghum BACs, which were in turn u sed to physically map the liguleless linkage group in sorghum. Results show a basic conservation of the liguleless region in sorghum relativ e to the linkage map of rice. One marker which is distal in rice is mo re medial in sorghum, and another marker which is found within the lin kage group in rice is on a different chromosome in sorghum. BACs assoc iated with linkage group I hybridize to chromosome I-t, which was iden tified by using FISH in a sorghum cytogenetic stock trisomic for chrom osome I (denoted I-t), and a BAC associated with linkage group E hybri dized to an unidentified chromosome. Selected BACs, representing RFLP loci, were end-cloned for RFLP mapping, and the relative linkage order of these clones was in full agreement with the physical data. Similar ities in locus order and the association of RFLP-selected BAC markers with two different chromosomes were found to exist between the linkage map of the liguleless region in maize and the physical map of the lig uleless region in sorghum.