The impact of the D genome and QTL in the A and B genomes on agronomic performance of hexaploid wheat and tetraploid durum was determined using novel recombinant inbred line populations derived from interploid crosses. Genetic differences between common hexaploid (6X) bread wheat (Triticum aestivum, 2n = 6x = 42, genome, AABBDD) and tetraploid (4X) durum wheat (T. turgidum subsp. durum, 2n = 4x = 28, genome, AABB) may exist due to effects of the D genome and allelic differences at loci in the A and B genomes. Previous work allowed identification of a 6X by 4X cross combination that resulted in a large number of fertile recombinant progeny at both ploidy levels. In this study, interspecific recombinant inbred line populations at both 4X and 6X ploidy with 88 and 117 individuals, respectively, were developed from a cross between Choteau spring wheat (6X) and Mountrail durum wheat (4X). The presence of the D genome in the 6X population resulted in increased yield, tiller number, kernel weight, and kernel size, as well as a decrease in stem solidness, test weight and seed per spike. Similar results were found with a second RIL population containing 152 lines from 18 additional 6X by 4X crosses. Several QTL for agronomic and quality traits were identified in both the 4X and 6X populations. Although negatively impacted by the lack of the D genome, kernel weight in Mountrail (4X) was higher than Choteau (6X) due to positive alleles from Mountrail on chromosomes 3B and 7A. These and other favorable alleles may be useful for introgression between ploidy levels.

The expanding geographical range of wheat stem sawfly (WSS) damage, coupled with the limited number of effective control measures, calls for a need to better characterize and explore the genetic variability for resistance in wheat (Triticum aestivum L.) germplasm from North America. An association‐mapping analysis for stem solidness and wheat stem sawfly resistance was conducted using a set of 244 elite spring wheat lines from 10 North American breeding programs. Three previously identified quantitative trait loci (QTL) for resistance were confirmed, including QTL for stem solidness, heading date, and stem cutting. Three new QTL on chromosomes 2A, 3A, and 5B were identified to be associated with larval mortality and a QTL associated with early stem solidness was identified on chromosome 5D. Genetic variation for late stem solidness is mainly determined by the solid‐stem QTL on chromosome 3B, while variation for early solidness is affected by chromosomal regions on 1B, 3B, and 5D. Potential sources of a novel resistance mechanism causing larval mortality were identified among the panel lines. Favorable alleles for stem solidness and other resistance traits are available within North American wheat germplasm, but only Montana and South Dakota breeding programs appear to have favorable alleles for all QTLs detected in this study. Improvements in wheat stem sawfly management, for both historically impacted areas and for regions first experiencing damage, may be obtained using alleles that already exist in elite germplasm.

Hexaploid bread wheat (Triticum aestivum L.) and tetraploid durum wheat (Triticum durum Desf.) have been cultivated in similar geographic areas for ∼10,000 yr. The crossing barrier caused by ploidy difference suggests that different favorable alleles for yield-related traits may have accumulated in the two crops. Previous work allowed identification of favorable alleles at six quantitative trait loci (QTL) from durum wheat in a recombinant inbred line (RIL) population from a cross of 'Mountrail' durum and 'Choteau' spring wheat. The purpose of this study was to determine the impact of six durum alleles at yield component QTL in several spring wheat backgrounds. Three spring wheat cultivars were crossed with six hexaploid lines derived from the original Choteau/Mountrail cross to generate RILs. Heterozygous RILs, containing both the durum and the bread wheat alleles, were identified for each of the QTL. The heterozygous RILs were used to develop near-isogenic lines (NILs) for the six introgressed QTL. The NILs were grown in five environments under irrigated and rainfed conditions in Montana in 2017 and 2018. A durum allele QTL on chromosome 3B resulted in increased kernel weight in all five environments. The introgressed durum QTL alleles caused pleiotropic interactions among yield component traits. Environment and genetic background significantly affected the stability of introgressed QTL on yield components for four of the six QTL. Results suggest that alleles from durum may be useful for yield improvement of hexaploid spring wheat. However, interrelationships of yield components, pleiotropic interactions, and environment will affect the value of durum wheat alleles in hexaploid wheat backgrounds.

Introduction of genes from outside a primary germplasm base has the potential to impact phenotypic diversity, genetic structure, and patterns of linkage disequilibrium (LD). Our goals were to monitor the introduction of key genes in a hard red spring wheat {Triticum aestivum L.) germplasm set using historical cultivars, to determine the impact of the introduced genes on phenotypic diversity in elite germplasm, and to assess the impact of selection history on LD. A superior alíele for bread making was introduced early in the 20th century and quickly became fixed. An alíele for solid stems introduced in the mid 20th century is the major source of variation in current germplasm. An introduced alíele for photoperiod insensitivity is an important source of variation for heading date in current germplasm. The allelic introductions impacted patterns of LD. The unlinked loci for reduced height, RHT-B1 and RHT-D1, were in LD. Linkage disequilibrium for physically linked markers near introduced genes did not exceed previous estimates of genome-wide LD. Our results showed a pattern of gene introductions into the spring wheat germplasm base that continues to have an impact on phenotypic diversity and patterns of LD.