Repeat-length variation in a wheat cellulose synthase-like gene is associated with altered tiller number and stem cell wall composition.

The tiller inhibition gene (tin) that reduces tillering in wheat (Triticum aestivum) is also associated with large spikes, increased grain weight, and thick leaves and stems. In this study, comparison of near-isogenic lines (NILs) revealed changes in stem morphology, cell wall composition, and stem strength. Microscopic analysis of stem cross-sections and chemical analysis of stem tissue indicated that cell walls in tin lines were thicker and more lignified than in free-tillering NILs. Increased lignification was associated with stronger stems in tin plants. A candidate gene for tin was identified through map-based cloning and was predicted to encode a cellulose synthase-like (Csl) protein with homology to members of the CslA clade. Dinucleotide repeat-length polymorphism in the 5'UTR region of the Csl gene was associated with tiller number in diverse wheat germplasm and linked to expression differences of Csl transcripts between NILs. We propose that regulation of Csl transcript and/or protein levels affects carbon partitioning throughout the plant, which plays a key role in the tin phenotype.

A QTL on chromosome 6A in bread wheat (Triticum aestivum) is associated with longer coleoptiles, greater seedling vigour and final plant height.

Wheat crops with greater early vigour shade the soil surface more rapidly and reduce water loss. Evaporative losses affect water-use efficiency particularly in drier regions where most of the rainfall occurs early in the growing season before canopy closure. Greater seedling leaf area and longer coleoptiles are major determinants of increased vigour and better crop establishment. A previously developed high vigour breeding line 'Vigour 18' was used to establish a large recombinant inbred family and framework map to identify a QTL on chromosome 6A that accounted for up to 8% of the variation for coleoptile length, 14% of seedling leaf width and was associated with increased plant height. The SSR marker NW3106, nearest to the 6A QTL, was also associated with greater leaf width in a breeding population that was also derived from a cross involving the high vigour donor line 'Vigour18'. The association between the NW3106 marker and coleoptile length was validated in a second breeding population which was developed using an unrelated long coleoptile donor line. The 'Vigour18' allele of the QTL on chromosome 6A promoted coleoptile length and leaf width during early plant growth but was also associated with increased plant height at maturity. Markers linked to the QTL are being used to increase the frequency of increased vigour and long coleoptile alleles in early generations of breeding populations.