Genetic and physiological bases for variation in water use efficiency in canola

Drought stress due to water deficiency threatens production of canola worldwide. Carbon isotope discrimination (Δ¹³C), a trait that can be used to assess efficient water use, provides an opportunity to exploit natural variation in canola for stable production. Here, we show that substantial genetically controlled phenotypic variation in water use efficiency (WUE) component trait, Δ¹³C (20.4 to 23.6‰) exists among accessions of canola. Quantitative trait loci (QTL) analysis revealed ten loci for Δ¹³C, each accounting for 2.5% to 16.5% of the genotypic variation. One of the significant QTL for Δ¹³C was co-localized with a QTL for flowering time, a trait implicated in drought escape and was mapped in the vicinity of the FLOWERING LOCUS T (FT) on chromosome A07. Gene expression analyses revealed that among FT paralogs, BnC6.FTb expression was significantly correlated (r = 0.33, p <.01) with variation in Δ¹³C across at least two environments in a canola DH population. Integration of data based on instantaneous single leaf gas exchange, dry matter Δ¹³C, and whole plant measurements suggests a possible trade-off between early flowering and WUE. Our findings provide insights into the complexity of Δ¹³C and WUE which could enable the development of canola varieties resilient to drought and increasing canola productivity under water-limited conditions.