Canopy architectural and physiological characterisation of near-isogenic wheat lines differing in the tiller inhibition gene tin

Tillering is a core constituent of plant architecture, and influences light interception to affect plant and crop performance. Near-isogenic lines (NILs) varying for a <i>t</i>iller <i>in</i>hibition (<i>tin</i>) gene and representing two genetic backgrounds were investigated for tillering dynamics, organ size distribution, leaf area, light interception, red: far-red ratio, and chlorophyll content. Tillering ceased earlier in the <i>tin</i> lines to reduce the frequencies of later primary and secondary tillers compared to the free-tillering NILs, and demonstrated the genetically lower tillering plasticity of <i>tin</i>-containing lines. The distribution of organ sizes along shoots varied between NILs contrasting for <i>tin</i>. Internode elongation commenced at a lower phytomer, and the peduncle was shorter in the <i>tin</i> lines. The flag leaves of <i>tin</i> lines were larger, and the longest leaf blades were observed at higher phytomers in the <i>tin</i> than in free-tillering lines. Total leaf area was reduced in <i>tin</i> lines, and non-<i>tin</i> lines invested more leaf area at mid-canopy height. The tiller economy (ratio of seed-bearing shoots to numbers of shoots produced) was 10% greater in the <i>tin</i> lines (0.73–0.76) compared to the free-tillering sisters (0.62–0.63). At maximum tiller number, the red: far-red ratio (light quality stimulus that is thought to induce the cessation of tillering) at the plant-base was 0.18–0.22 in <i>tin</i> lines and 0.09–0.11 in free-tillering lines at levels of photosynthetic active radiation of 49–53% and 30–33%, respectively. The <i>tin</i> lines intercepted less radiation compared to their free-tillering sisters once genotypic differences in tiller numbers had established, and maintained green leaf area in the lower canopy later into the season. Greater light extinction coefficients (<i>k</i>) in <i>tin</i> lines prior to, but reduced <i>k</i> after, spike emergence indicated that differences in light interception between NILs contrasting in <i>tin</i> cannot be explained by leaf area alone but that geometric and optical canopy properties contributed. The careful characterization of specifically-developed NILs is refining the development of a physiology-based model for tillering to improve understanding of the value of architectural traits for use in cereal improvement.