Wheat Response to Increasing Temperatures: The Role of Genetic Variability.

In the last 50 years, Australia’s mean temperature has increased by approximately 0.7 ^₀C and up to 2.0 ^₀C in some areas, with the strongest warming observed in spring. The potential impact of projected temperature increases on Australian wheat production and yield is important and will likely occur by affecting negatively different processes, e.g. indirectly by shortening the tillering phase and more directly if heat shock temperatures reduce floret fertility and grain set. Our hypothesis is that there is available genotypic variability in wheat to minimise the impact of high temperatures on yield. This was tested in an experiment in growth rooms where wheat lines differing for water soluble carbohydrate (WSC) accumulation, tillering, transpiration efficiency, floret fertility and grain size were subjected to either raised (33/14 °C) or optimum (24/14 °C) average temperature. In addition, to examine the effects of heat shock, two genotypes were grown in a 24/14 °C room and moved into the 33/14 °C at particular developmental stages for 3 days, specifically when leaf 5 was fully emerged, the start of stem elongation, the distance between the flag and penultimate leaves was 1 cm and anthesis.  All rooms had a 16 hour photoperiod and relative humidity set to maintain the vapour pressure deficit. Our methods included measurements for leaf and tiller development, SPAD measurements and gas exchange levels, canopy temperature, floret fertility, biomass at anthesis and maturity, grain yield components as well as levels of N and WSC.