Agronomic evaluation of a tiller inhibition gene (tin) in wheat.: II.: Growth and partitioning of assimilate

Wheats with reduced tillering have been proposed for areas regularly subject to a terminal drought. A wheat plant with a genetic disposition to produce fewer stems is now possible through the introgression of a gene that inhibits tillering ( tin). This study was conducted to determine the effect of the tin gene on the dynamics of tillering, light interception, and dry-matter production and partitioning in several different cultivars of wheat. Commercial cultivars and their near-isogenic pairs differing in the presence of the tin gene were grown in well-watered tubes and also in the field in south-eastern Australia where terminal drought is common. Tiller number, light interception, leaf area index (LAI), biomass, and the partitioning of biomass were recorded at various intervals throughout the growing season. Water-soluble carbohydrate (WSC) levels in the stems of field-grown plants were also determined in some environments at anthesis and maturity. In tubes and in field environments, lines with the tin gene produced tillers at the same rate as their free tillering counterparts but ceased tillering sooner. Under conditions where the free tillering lines produced over 1000 shoots/m(2), lines containing the tin gene produced 600 shoots/m(2). However, by maturity, fertile spike numbers were 450 and 350/m(2) for lines with and without the tin gene, respectively. Despite the large difference in tillering, there were only small differences in LAI, light interception throughout the season, and biomass. There were small differences in the proportional allocation of biomass, and the tin lines partitioned more of their biomass towards spikes at anthesis and stored more WSC in stems. Dry weight distribution varied with genetic background, but in general the tin gene increased leaf area ratio and root to shoot ratio but decreased specific leaf area. It is concluded that the tin gene may be advantageous under terminal drought. This would come from the reduced light interception prior to anthesis and thereby potential for greater transpiration during grain filling as well as a greater capacity for stem carbohydrate storage and remobilisation. These factors are consistent with a greater harvest index and kernel weight associated with lines containing the tin gene.