The supernumerary spikelets (SS) characters of tetraploid wheat (Triticum turgidum L.) resulting in more spikelets and kernels per spike, thus enhancing sink capacity may contribute to potential wheat yield improvement.  In order to investigate the effect of different SS types on agronomic characters and understand the genetic base of SS phenotype in tetraploid wheat, near isogenic lines (NILs), bh-50 with normal spikelets (NS), bh-51 with four-rowed spikelets (FRS), bh-52 with short-ramified spikelets (SRS), and bh-53 with long-ramified spikelets (LRS) in a Triticum durum cv. ZY1286 genetic background were developed by continuous backcrossing.  Agronomic characters showed that the SS phenotype lines, bh-51, bh-52 and bh-53 have significant increase in the number of spikelets and grains per spike compared with the NS phenotype line bh-50 (P<0.05), and bh-53 line showed much more increase than those of bh-51 and bh-52.  However, bh-53 had the lowest grain weight and the longest spike development stage than those of other spike phenotypes.  These results indicated that the different SS types have different effects on the agronomic and spike characters.  Genetic analysis through bh-50/bh-51 and bh-51/bh-53 F₂ populations showed that a recessive major gene controlled the spike architecture to transform from NS to FRS, and a dominant major gene determined the change of spike phenotype from FRS to RS.  DNA sequences of TtBH/WFZP ortholog on chromosome 2AS revealed that a single nucleotide polymorphism (SNP) substitution happened in the open reading frame (ORF) region of all the SS tetraploid wheat accessions, which may lead to the generation of lateral meristems between glume and lemma during the immature spike development.  While the fates of the lateral meristems, developing into lateral spikelets or branched spikelets, may be determined by another major gene.  Our results presented here may advance our understanding and knowledge of the genes and genetic pathways determining the spike architecture development in wheat.