The domestication and subsequent genetic improvement of wheat led to the development of large-seeded cultivated wheat species relative to their smaller-seeded wild progenitors. While increased grain weight (GW) continues to be an important goal of many wheat breeding programs, few genes underlying this trait have been identified despite an abundance of studies reporting quantitative trait loci (QTL) for GW. Here we perform a QTL analysis for GW using a population of recombinant inbred lines (RILs) derived from the cross between wild emmer wheat accession ‘Zavitan’ and durum wheat variety ‘Svevo’. Identified QTLs in this population were anchored to the recent Zavitan reference genome, along with previously published QTLs for GW in tetraploid wheat. This genome-based, meta-QTL analysis enabled the identification of a locus on chromosome 6A whose introgression from wild wheat positively affects GW. The locus was validated using an introgression line carrying the 6A GW QTL region from Zavitan in a Svevo background, resulting in >8% increase in GW compared to Svevo. Using the reference sequence for the 6A QTL region, we identified a wheat ortholog to OsGRF4, a rice gene previously associated with GW. The coding sequence of this gene (TtGRF4-A) contains four single nucleotide polymorphisms (SNPs) between Zavitan and Svevo, one of which reveals the Zavitan allele to be rare in a core collection of wild emmer and completely absent from the domesticated emmer genepool. Similarly, another wild emmer accession (G18-16) was found to carry a rare allele of TtGRF4-A that also positively affects GW and is characterized by a unique SNP absent from the entire core collection. These results exemplify the rich genetic diversity of wild wheat, posit TtGRF4-A as a candidate gene underlying the 6A GW QTL, and suggest that the natural Zavitan and G18-16 alleles of TtGRF4-A have potential to increase wheat yields in breeding programs.

Drought is the major environmental factor limiting wheat production worldwide. Developing novel cultivars with greater drought tolerance is the most viable solution to ensure sustainable agricultural production and alleviating threats to food-security. Here we established a core-collection of landraces and modern durum wheat cultivars (WheatME, n = 36), from the Middle East region (Jordan, Palestine and Israel) aiming at unlocking the genetic and morpho-physiological adaptation to semi-arid environment conditions. Interestingly, genetic analysis of the WheatME core-collection could not distinguish the landraces according to their country of origin. Field-based evaluation of the core-collection conducted across range of contrasting environmental conditions: Til-Palestine, Bet-Dagan-Israel and Irbid-Jordan with annual precipitation of 500 mm, 360 mm and 315 mm, respectively. The Til environment showed highest grain yield while the Irbid environment showed the lowest values. Analysis of variance showed a significant Genotype × Environment interaction for plant phenology traits (plant height and heading date) and productivity traits (1000-kernel weight, and grain yield). Principal component analysis showed three main cultivar groups: High yielding lines (modern durum cultivars, and landraces), tall late flowering landraces, and landraces with high grain weight. This knowledge could serve as basis for future breeding efforts to develop new elite cultivars adapted to the Mediterranean Basin’s semi-arid conditions.

Wheat domestication and subsequent improvement formed a wide phenotypic variation in Grain Weight (GW) between the domesticated wheat species and their wild progenitors. GW continues to be an important goal of many wheat-breeding programs and yet, although studies found many quantitative trait loci (QTLs) for GW, not many genes that underlay these loci were identified. Here we performed QTL analysis for GW using a Recombinant Inbred Line (RIL) population based of a cross between wild emmer wheat accession 'Zavitan' and durum wheat variety 'Svevo'. Using the recent Zavitan genome assembly, we anchored the identified QTLs to the reference sequence and added the positions of previously published QTLs for GW in tetraploid wheat. This genome based meta-QTL analysis enabled us to identify a locus on chromosome 6A with a positive effect on GW that was contributed by wild wheat in a few studies. This locus was validated using an introgression line that contains the 6A GW QTL from Zavitan in the background of Svevo with higher grain weight. Using the reference sequence and genes associated with GW from rice, we were able to identify a wheat ortholog in the 6A QTL region to rice gene, OsGRF4. The coding sequence of this gene, TtGRF4-A, showed four SNPs between Zavitan and Svevo. Molecular marker developed for the first SNP showed that the Zavitan allele of TtGRF4-A is rare in a core collection of wild emmer and absent in domesticated emmer genepool. We suggest that TtGRF4-A is a candidate underlying the 6A GW QTL and breeding with its natural Zavitan allele may have the potential to increase wheat yields. . Faris, J. D.; Zhang, Q.; Chao, S.; Zhang, Z.; Xu, S. S. Analysis of agronomic and domestication traits in a durum × cultivated emmer wheat population using a high-density single nucleotide