In this study, two hydroponic experiments were carried out in a nutrient solution growth system in a growth chamber to determine the morphological and physiological background of nitrogen efficiency in pepper (Capsicum annuum L.). In the first
experiment, 16 pepper inbred lines and 2 pepper commercial rootstocks were screened under 2 nitrogen (N) doses (0.3 mM and 3.0 mM N) in a completely randomized block design with 3 replications. In the second experiment, four pepper lines (N-efficient: 21-H- 1-1 and AH-2-3, N-inefficient: ERU 1248 and 24-H-6) selected in the first stage of the study were grafted reciprocally and tested under 2 N doses. By using nitrogen efficient lines (21-H-1-1/24-H-6, 21-H-1-1/ERU 1248, AH-2-3/ERU 1248, AH-2-3/24-H-6) as rootstocks increased growth and biomass production compared to non-grafted control plants (N-inefficient), while using N-efficient lines (1248/21-H-1-1, ERU 1248/AH-2-3, 24-H-6/21-H-1-1, 24-H-6/AH-2-3) as scion (ERU caused lower shoot growth than the control (N-efficient). It is also seen that well-developed strong root systems are the most important factor contributing to N use efficiency in pepper.