Elevated CO 2 Reduced Floret Death in Wheat Under Warmer Average Temperatures and Terminal Drought.

Eduardo Dias De Oliveira,Helen Bramley,Jairo A Palta,Kadambot H M Siddique,Katia Stefanova

doi:10.3389/fpls.2015.01010

Abstract

Elevated CO2 often increases grain yield in wheat by enhancing grain number per ear, which can result from an increase in the potential number of florets or a reduction in the death of developed florets. The hypotheses that elevated CO2 reduces floret death rather than increases floret development, and that grain size in a genotype with more grains per unit area is limited by the rate of grain filling, were tested in a pair of sister lines contrasting in tillering capacity (restricted- vs. free-tillering). The hypotheses were tested under elevated CO2, combined with +3°C above ambient temperature and terminal drought, using specialized field tunnel houses. Elevated CO2 increased net leaf photosynthetic rates and likely the availability of carbon assimilates, which significantly reduced the rates of floret death and increased the potential number of grains at anthesis in both sister lines by an average of 42%. The restricted-tillering line had faster grain-filling rates than the free-tillering line because the free-tillering line had more grains to fill. Furthermore, grain-filling rates were faster under elevated CO2 and +3°C above ambient. Terminal drought reduced grain yield in both lines by 19%. Elevated CO2 alone increased the potential number of grains, but a trade-off in yield components limited grain yield in the free-tillering line. This emphasizes the need for breeding cultivars with a greater potential number of florets, since this was not affected by the predicted future climate variables.

Highlights

Atmospheric CO2, ambient temperature and rainfall are environmental variables predicted to change in Mediterranean-type environment in the in the 21st century with climate change (Ragab and Prudhomme, 2002; Asseng et al, 2004)
Time to anthesis was affected by a CO2 × temperature interaction (P = 0.005), where elevated CO2 reduced the time to anthesis by 2 days under ambient temperature only
Any prediction of increased grain yield due to more tillers produced was not attained because the trade-off between yield components limited grain yield in the free-tillering line

Summary

Introduction

Atmospheric CO2, ambient temperature and rainfall are environmental variables predicted to change in Mediterranean-type environment in the in the 21st century with climate change (Ragab and Prudhomme, 2002; Asseng et al, 2004). Rainfall in particular, is predicted to decrease when wheat crops enter the reproductive growth (terminal drought), reducing grain yield (Ludwig and Asseng, 2006; Turner et al, 2011). Grain yield in a free-tillering wheat line, with the potential to increase sink capacity, did not differ from its isogenic restricted-tillering line, with lower sink capacity. This was because the free-tillering line increased grain number per unit area due to elevated CO2, but had smaller grains (Dias de Oliveira et al, 2015), presumably due to the negative correlation between grain number per unit area and grain size (Grafius, 1972). Understanding the mechanisms determining grain number per unit area and grain size is, important in simultaneously increasing both yield components (Reynolds et al, 2009; Fischer, 2011; Ferrante et al, 2013b)

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