Technical Abstract: An insertion/deletion size variant located at the csLV34 locus on chromosome 7D within an intron sequence of a sulphate transporter-like gene tightly linked to the Lr34/Yr18 dual rust resistance was used to examine a global collection of wheat cultivars, landraces and D genome containing diploid and polyploid species of wheat relatives. Two predominant allelic size variants, "csLV34a" and "b" were found among the wheat cultivars and showed disparate variation in different wheat growing zones. A strong association was observed between the presence of Lr34/Yr18 and csLV34b allele and the simultaneous occurrence of established sources of Lr34/Yr18 with csLV34a allele was rare. All landraces with the exception of those from China were predominantly of the csLV34a type. Only one size variant, csLV34a, was detected among the diploid and polyploid D genome containing species, implicating csLV34b as having arose subsequent to hexaploid bread wheat synthesis. The lineage of the csLV34b allele associated with Lr34/Yr18 in a significant proportion of modern wheat cultivars from North and South America, CIMMYT, Australia and Russia was tracked back to the older cultivars Mentana and Ardito developed in Italy by Nazareno Strampelli in the early 1900s.