C-13 ISOTOPE DISCRIMINATION AT SEVERAL GROWTH-STAGES IN LENTIL, SPRING WHEAT AND CANOLA

CID has been proposed to indirectly select for transpiration efficienc y and seed yield in C-3 plants. Before using CID as an indirect select ion criterion it is important for plant breeders to determine the best growth stage at which to sample for CID. Consequently, to determine t he most effective growth stage to select for CID we measured: (i) seve ral growth stages to determine the one that provides the maximum diffe rential for CID, (ii) the magnitude of die genotype by growth stage in teraction for CID, and (iii) the variability for CID within and among genotypes of two divergent genotypes of lentil (Lens culinaris Medikus ), spring wheat (Triticum aestivum L.) and canola (Brassica napus L.). Three plants per pot were grown hydroponically in a glasshouse using a RCBD replicated four times. Three samples were collected at four gro wth stages: early vegetative, late vegetative, flowering and maturity. The variability for CID among plants within genotypes was small. The two lentil genotypes differed significantly in CID; whereas, no signif icant differences were observed for the wheat or canola genotypes. In all three crops the genotype by growth stage interaction for CID was n ot significant, and the best differential for CID among lentil genotyp es was mature seed. The ranking of genotypes remained constant across growth stages; therefore, sampling for CID may be done at any stage of plant development.