Authors: Gaju, O., De Silva, J., Carvalho, P. and Foulkes J.
With harvest index approaching a plateau it appears most future genetic improvement in wheat grain yield will come from increased biomass. Our objective is to identify traits determining novel genetic variation in biomass and nitrogen-use efficiency (grain yield / available N; NUE) in bread wheat. A field experiment was carried out examining 240 genotypes (119 landraces , 63 European wheat cultivars , 40 synthetic-derived wheats and 10 UK elite cultivars) at high and low N in 2010/11 and 2011/12 at Nottingham University, UK. Grain yield, biomass and NUE were measured from machine-harvested yields and analysis of DM and N partitioning. The Normalized Difference Vegetative Index (CropScan MSR 16 R spectro-radiometer) and percentage green flag-leaf area (visual key - 0 to 10 ; 10 = 100% senesced) were assessed weekly from flag-leaf emergence to maturity. Fifteen genotypes were selected for weekly assessment of flag-leaf light-saturated photosynthetic rate (Amax) using a Li-Cor LI-6400XT Photosynthesis System weekly and flag-leaf chlorophyll content (SPAD) at anthesis.
The genotypes differed in biomass and NUE (P<0.001) with the synthetic derivatives generally maintaining biomass and NUE better under low N than other genotypes. Positive associations amongst genotypes between NDVI and biomass (R2=0.47, P<0.001) and onset of senescence and grain yield (R2= 0.21; P<0.001) were observed under low N. Genotypes differed in Amax with the synthetic derivatives (23.8 μmol m-2 s-1) and elite cultivars (24.1 μmol m-2 s-1) generally having higher Amax than the landraces (19.7 μmol m-2 s-1) under high N (P< 0.001). Amax was positively associated with biomass (R2=0.58, P< 0.001) amongst the genotypes in 2010-11 and grain yield averaged over years (R2=0.88, P<0.001). A positive association was also found between Amax and flag-leaf SPAD value at GS61 (R2 = 0.82; P< 0.001). Work is ongoing to identify the genetic basis of this novel trait variation.
Acknowledgment
This work is funded by BBSRC as part of the Wheat Improvement Strategic programme (WISP). This work was carried out as part of the WISP collaborative project joint with Rothamsted Research, John Innes Centre, University of Bristol and NIAB.