Rust and powdery mildew diseases of wheat are among the oldest and most harmful diseases confining the yield of wheat worldwide. Development of resistant wheat cultivars with durable or race-nonspecific resistance genes is the main objective for many breeding programs. One of these genes, Lr34/Yr18/Pm38, was found to confer partial and durable resistance against rust pathogens as well as powdery mildew. This multiple disease resistant locus was recently found to comprise a single gene, which encodes an adenosine triphosphate-binding cassette transporter (ABC-transporter) of the pleiotropic drug resistance (PDR) subfamily. Differences in the alleles of resistant and susceptible cultivars enabled to develop six allele-specific markers. In this study, 46 different Turkish bread wheat cultivars were screened using these specific markers, which indicated that 13 cultivars carry the resistance allele of that gene. To compare this molecular finding with phenotypic observations, a field trial with artificial inoculation of Puccinia recondita was performed. Interestingly, all cultivars having the resistance allele were found to be susceptible. Although Lr34 has mediated resistance against leaf rust for over 40 years and has been used globally as an effective component of rust resistance in many breeding programs, this adult plant resistance is ineffective in the studied Turkish bread wheat cultivars.