Molecular and comparative mapping of genes governing spike compactness from wild emmer wheat

The development and morphology of the wheat spike is important because the spike is where reproduction occurs and it holds the grains until harvest. Therefore, genes that influence spike morphology are of interest from both theoretical and practical stand points. When substituted for the native chromosome 2A in the tetraploid Langdon (LDN) durum wheat background, the Triticum turgidum ssp. dicoccoides chromosome 2A from accession IsraelA confers a short, compact spike with fewer spikelets per spike compared to LDN. Molecular mapping and quantitative trait loci (QTL) analysis of these traits in a homozygous recombinant population derived from LDN x the chromosome 2A substitution line (LDNIsA-2A) indicated that the number of spikelets per spike and spike length were controlled by linked, but different, loci on the long arm of 2A. A QTL explaining most of the variation for spike compactness coincided with the QTL for spike length. Comparative mapping indicated that the QTL for number of spikelets per spike overlapped with a previously mapped QTL for Fusarium head blight susceptibility. The genes governing spike length and compactness were not orthologous to either sog or C, genes known to confer compact spikes in diploid and hexaploid wheat, respectively. Mapping and sequence analysis indicated that the gene governing spike length and compactness derived from wild emmer could be an ortholog of the barley Cly1/Zeo gene, which research indicates is an AP2-like gene pleiotropically affecting cleistogamy, flowering time, and rachis internode length. This work provides researchers with knowledge of new genetic loci and associated markers that may be useful for manipulating spike morphology in durum wheat.