Grain yield responsiveness to water supply in near-isogenic reduced-tillering wheat lines - An engineered crop trait near its upper limit

Grain yield responsiveness to water supply was evaluated in spring wheat (Triticum aestivum L.) near-isogenic lines (NILs) for presence of the reduced-tillering 'tin' (tiller inhibition) gene using boundary-line analysis. Data were collected from multiple seasons at Managed Environment Facilities (MEFs; field experimental facilities to control and target water supply) at three locations across the Australian wheatbelt. The minimum water required to obtain a measurable yield was less in reduced-tillering than free-tillering NILs (70 vs 95 mm). Above this minimum, for every mm increase in water supply, grain yield in free-tillering lines increased more rapidly (that is, showed greater responsiveness) than reduced-tillering lines (15.4 vs 12.6 kg ha(-1) mm(-1)). This difference suggests the reduced-tillering gene is associated with greater yield potential in situations with water supply of less than 200 mm. Reduced-tillering wheat also affords a 0.3 t ha(-1) yield benefit in extremely water-limited, low yielding situations where no measurable yield is expected with free-tillering wheats (i.e. at water supply 95 mm). These specific adaptations need to be considered when contemplating the use of reduced-tillering wheats in dryland systems where water is a key limiting factor.