THE EFFECT OF DWARFING GENES IN SPRING WHEAT IN DRY ENVIRONMENTS .2. GROWTH, WATER-USE AND WATER-USE EFFICIENCY

Near-isogenic lines of wheat for the dwarfing genes Rht1, Rht2, Rht1 + Rht2 as well as tall (rht) lines were grown in dryland field environments over 7 years as well as in large pots outside and in a glasshouse. In the field above-ground dry weight and leaf area index up to maturity were greater in the taller wheats. In pot experiments there were no differences in relative growth rates between lines and the faster emergence of the tall wheats accounted for most of the difference in dry weight accumulation and leaf canopy development. Tall wheats also had a slightly higher carbon isotope discrimination which has been related to faster canopy growth in wheat. Water extraction by tall and dwarf wheats was similar in both 1 m long tubes and down to a depth of 1.9 m in the field. However, transpiration efficiency (above-ground dry weight/water transpired) and water-use efficiency (above-ground dry weight/evapotranspiration) declined with plant height in both glasshouse and field experiments. There was no evidence that tall wheats had a greater capacity for storage and remobilization of photosynthate in the stems than shorter wheats. The implications for crop improvement in dry regions are discussed.