Towards Positional Cloning of Qyld.Idw-3B, a Major QTL for Grain Yield Per Se in Durum Wheat

In durum wheat, a major QTL (QYld.idw-3B) for plant height, peduncle length, stay-green, leaf greenness, thousand kernel weight and grain yield per se across a broad range of soil moisture was identified in a RIL population derived from Kofa and Svevo (Maccaferri et al. 2008, Genetics). The fine mapping of QYld.idw-3B is underway in the framework of the FP7 TriticeaeGenome project. In this regard, three pairs of NILs with contrasted haplotypes at the target region were crossed to produce ca. 7,500 F₂ plants that were screened for the identification of recombinants within the 11 cM interval between Xgwm389 and Xgwm493 that flanked the QYld.idw-3B peak. A total of 250 homozygous F_4:5 segmental isolines were evaluated in the field and profiled molecularly. To increase the map resolution in the target region, new polymorphic markers were identified by exploiting the sequence information produced from the assembly of the chr. 3B physical map of bread wheat (Paux et al. 2008, Science). A total of 50 new markers (BAC-derived SSR, ISBP and SNP markers) have been added to the target interval. All markers were anchored to the Chinese Spring physical map of chr. 3B, which allowed us to identify the BAC contigs spanning the QTL region. A high-resolution map has been obtained with an average marker distance of 0.25 cM. QYld.idw-3B has been confined to a 2 cM interval spanned by Contig 954 of Chinese Spring which contains 42 genes (Choulet et al. 2010, Plant Cell). The functional characterization via transcriptomics of these genes is underway.