Nitrogen efficiency of canola genotypes varies between vegetative stage and grain maturity

There is no information on whether N efficiency in canola at maturity can be reliably determined by screening germplasm in the vegetative stage. Twelve canola genotypes identified in preliminary screening study as having either high or low N efficiency indices were tested for consistency in N efficiency between the vegetative stage and maturity. Plants were grown in a glasshouse under low or adequate N supply and N efficiency was assessed using the following criteria: dry weight at deficient N supply, relative yield at low vs. adequate N supply, and N utilisation efficiency. None of the 12 tested genotypes was classified as efficient or inefficient under all three criteria. One genotype (46C74) was classified as efficient under two criteria, and one genotype (Surpass 300 TT) was inefficient under two criteria. At maturity, three additional efficiency criteria were used: harvest index, N harvest index, and oil and protein concentration in seed. Two genotypes (Wesway and 46C74) (ranked as efficient at vegetative stage) remained efficient at maturity under most of the efficiency criteria used. On the other hand, genotype Surpass 603 CL ranked inefficient during the vegetative stage was ranked as efficient at maturity under two criteria. Overall, there was little consistency in the N efficiency ranking between vegetative stage and maturity in 12 tested genotypes. Screening canola germplasm for N efficiency for breeding purposes would therefore require an assessment at maturity.