Variation in carbon isotope discrimination and its relationship to specific leaf area and ribulose-1,5-bisphosphate carboxylase content in groundnut genotypes

Variation in cahn isotope discrimination (Δ) and ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) content per unit leaf area was examined in leaves from upper and lower positions in the canopy of six groundnut (Arachis hypogaea L.) genotypes, grown under irrigated and mild water-deficit conditions in the field. The leaf mass per unit leaf area (ρL) and soluble proteins in leaves were determined at 80, 96, 111 and 127 days after sowing (DAS), while Δ and Rubisco were determined at 80 DAS only. The mean Δ ranged from 18.2 to 20.20 among genotypes, representing a significant (P 60%) attributable to Rubisco content per unit leaf area. In view of the leaf positional effects on Δ and Rubisco, the upper leaves in the canopy should be used for selecting genotypes for W based on leaf traits like ρL or Δ.