| Nitrogen compound contains protein, free amino acid , alkaloid, nitrate and tobacco-specific nitrosamines (TSNA) in tobacco leaves. The nitrate, nitrite and alkaloids are precursor to form tobacco-specific nitrosamines (TSNA). It is of great importance to know genetic variation of these precursor in decreasing the TSNA content and improving the quality and safety of tobacco leaves by genetic improvement. Experiments were located in Xinyang, Zhengzhou and Shangqiu cities in 2001. According to the method No. 2 of Griffing's dialle mating design, a set of 6 parents with different genetic basis and their 15 F1 crosses were made. Genetic variation, combining ability effects and stability of the content of 4 nitrogen components in flue-cured tobacco leaves were analyzed. Main conclusions were as follows:1 The results of joint analysis of variance in multiple locations, descriptive statistics analysis and multiple comparison indicated that the variation of several nitrogen components containing nitrate, nitrite, nicotine, total nitrogen in flue-cured tobacco leaves are significant or highly significant among different genotypes, environments and leaf positions. So there existed widely variation for nitrogen components of flue-cured leaf.(1) As far as nitrate and nitrite be concerned, average content of nitrate of twenty-one genotypes was 2.83 ±0.68%, and coefficient of variation was 24.13%; average content of nitrite was 6.88 ± 1.70%, and coefficient of variation was 24.63%. Comparison among different parents showed that 8136, RG17 and Panyuanhuang hadthe high content and Hongda, Zhongyan90 and K326 had the low content; The trend was cutters > upper leaf >lugs among different leaf positions; Comparison among different locations showed that Shangqiu had the biggest content of nitrate and nitrite, and had significant difference with Xinyang and Zhengzhou at 1% level.(2) Considering content of nicotine and total nitrogen, average content of nicotine of twenty-one genotypes was 2.26 0.37%, and variation coefficient was 16.43%; average content of total nitrogen was 1.85 0.14%, and variation coefficient was 7.31%. The high variation coefficient among parents showed parents were more sensitive to environment than FI hybrids. The trend of content of nicotine of different positions was upper leaf >cutters >lugs. The variation of content of nicotine and total nitrogen was different from that of nitrate and nitrite among locations, genotypes and positions.2 The results of heritability in three locations indicated that the heredity of the content of four nitrogen components was controlled mostly by gene additive effects, and gene non-additive effect was also important. The range of hB2 of nitrate among locations was 59.07-66.8%, and h2N was 33.19-48.90%. The range of hB2 of nitrite among locations was 60.73-78.27%, and hN2 was 37.40-54.52%. The range of hB2 of nicotine among locations was 63.38 - 73.87%, and hN2 was 56.37-63.96%. The range of hB2 of total nitrogen among locations was 70.42 - 82.14%, and h2N was 41.60-69.23%. The hB2 of nitrate and nitrite of different positions showed the trend of upper leaf > lugs > cutters. The h2N was relatively low which indicated large non-additive effects. The hB2 of nicotine and total nitrogen among different positions showed lugs > cutters > upper leaf.3 Simple correlation analysis showed that the correlation coefficients of the content of both nitrate with nitrite and nicotine with total nitrogen were significant at 5% level. The correlation coefficients were 0.5610 and 0.7962, respectively. The correlation ofnitrite and nitrate with nicotine and total nitrogen weren't significant, respectively. The correlation between mid-parent and F1 hybrid was significant at 5% or 1% level, which indicated that it is effective to improve nitrogen components according to the correlation of parent-offspring.4 The results of analysis of variance of combining ability of four nitrogen components indicated that the variation of GCA and SCA were signific...
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