Nitrogen (N) is a major part of plant nutrition in agricultural ecosystems. It greatly affects the physiological processes and yield of crop species and genotypes, specially ''oilseed crops'' such as sesame, which possesses the highest oil quality and quantity among all oilseeds. In order to study the effect of N and genotype on the phenology, growth characteristics, seed yield components, seed yield, seed quality and also the gas exchanges of sesame leaves; an experiment was laid out in split plots based on randomized complete block design with three replications and 35 plants m -2 at the Lavark Research Farm, Isfahan University of Technology, in 2006. Three N levels (50, 100 and 150 Kg N ha -1 ) and seven sesame genotypes (Local Ardestan, Nonbracching Naz, Branching Naz, Yekta, Oltan, Darab 14 and Varamin 2822) were used in main and sub plots, respectively. Increasing N levels significantly delayed the occurrence of all phenological phases; decreased the seed oil content; and increased the net leaf photosynthetic rate, seed protein content, seed yield components, seed yield, oil and protein yield; due probably to a delay in the leaf senescence and also the enhancement in chlorophyll and photosynthetic enzyme contents of leaves. Among the genotypes, Nonbranching Naz and Branching Naz proved early and Local Ardestan, Darab 14 and Varamin 2822 proved late in terms of all phonological phases. Besides, in all phenological phases, except for the seedling phase; Yekta and Oltan indicated the highest LAI, though Local Ardestan and Branching Naz produced the lowest one. Prior to seed filling, the highest biological yield was detected in Local Ardestan and Branching Naz, whereas the lowest one was found in Nonbranching Naz, Yekta and Varamin 2822. During seed filling, however, probably owing to their LAI and LAD; Oltan produced the most while Local Ardestan and Branching Naz produced the least biological yield. The highest seed oil content obtained with Nonbranching Naz, Branching Naz and Yekta whereas the lowest one was with Local Ardestan. The net photosynthetic rate, seed protein content, seed yield components, seed yield, oil and protein yield were the highest in Yekta and Oltan, while they were the lowest in Local Ardestan and Branching Naz. It seems that, with the conditions under which this experiment was conducted, increasing N levels to at least 150 Kg N ha -1 , despite a decrease in seed oil content; leads to the higher net photosynthetic rate, seed yield, and also oil and protein yield. Since, Yekta and Oltan outperformed the rest of the genotypes, they could be recommended for sesame production in Isfahan .
