Characterization of pepper (Capsicum annuum L.) genotypes for zinc stress tolerance based on morphological traits

Zinc (Zn) stress negatively affects plant growth and physiology; however, genotypic variation influences the degree of tolerance. In this study, 28 genetically distinct Capsicum annuum genotypes were evaluated under hydroponic Zn stress (5 mM ZnCl₂) and control conditions. Morphological and physiological traits, including SPAD values, leaf number, shoot and root length, stem diameter, leaf dimensions, and biomass (fresh/dry weight), were measured. Genotypes P114, P82, and P116 exhibited minimal SPAD reductions (<5%), whereas P41, P161, and P159 showed >30% declines. P120, P45, and P171 maintained leaf number under stress, while root elongation increased in P164 and P50 by over 70%. Biomass retention was highest in P31, P164, and P161, while lowest in P173 and P49. Principal Coordinate Analysis (PCoA) identified P159, P164, P114, and P46 as Zn-tolerant genotypes. Strong correlations were found between fresh and dry weight (r = 0.90), root length and dry weight (r = 0.55), and leaf width and fresh weight (r = 0.46). These findings reveal key physiological traits linked to Zn tolerance and provide valuable insights for breeding stress-resilient pepper cultivars.