Triticum urartu possesses the Au genome common to bread wheat. Similarly, Triticum monococcum contains the Am genome, which is closely related to the A-genome donor of bread wheat. Aegilops speltoides of the Sitopsis section has the S genome, which is most similar to the B genome of bread and durum wheat when compared with all other wild grasses. Amphiploids developed through bridge crossing between Am/Au and S-genome diploid resources and elite durum cultivars demonstrate enormous diversity to improve both bread and durum wheat cultivars. We evaluated such A-genome amphiploids (Triticum turgidum × T. urartu and T. turgidum × T. monococcum, 2n = 6x = 42; BBAAAmAm/AuAu) and S-genome amphiploids (T. turgidum × Ae. speltoides, 2n = 6x = 42; AABBSS) along with their durum parents (AABB) for their resistance to powdery mildew (PM) at the seedling stage. The results indicated that 104 accessions (53.6%) of A-genome amphiploids (AABBAmAm/AuAu) were resistant to PM at the seedling stage. Of their 24 durum parents, five (20.83%) were resistant to PM and 16 (66.6%) were moderately tolerant. Similarly, ten (50%) accessions of S-genome amphiploids (BBAASS) possessed seedling PM resistance, suggesting a valuable source of major resistance genes. PM screening of the amphiploids and parental durum lines showed that resistance was contributed either by the diploid progenitors or durum parents, or both. We also observed the suppression of resistance in several cases; for example, resistance in durum wheat was suppressed in respective amphiploids. The results from this germplasm screening will facilitate their utilization to genetically control PM and widen the genetic base of wheat.