| Nitrogen is one of the indispensable macroelements for plants growth and development, and it is also an important elements to increase yield and quality. The eggplant needs a large number of nitrogen fertilizer in its whole growth period, but its nitrogen utilization efficiency is very low. Breeding varieties with high nitrogen use efficiency is the effective way. Based on the selected eggplant inbred lines with different nitrogen use efficiencies, the combining ability of nitrogen use efficiency (NUE) related traits in 7 inbred lines was analyzed in the field experiment using half-diallel corss method. The combination ability and other genetic parameters of root characters in seedlings of eggplants with different nitrogen use efficiencies were studied under two nitrogen levels by solution culture; The heterosis on enzyme activity of the nitrogen use efficiency was determinated in some F1 hybrids, which is important to gain experimental materials and theoretical basis in breeding eggplant cultivars with high nitrogen use efficiency. The main results obtained from this research are shown as follows:1. Based on the selected eggplant inbred lines with different nitrogen use efficiencies, the combination ability of nitrogen use efficiency related traits 7 inbred lines was analyzed under both levels of high N(450 kg-ha-1) and low N(no N) by Griffing-II design. The results showed that the characters,the general combining ability of all traits related to nitrogen use efficiency was significantly different at two N levels. NUE was controlled by addittive and non-additative effects, however the total uptake N and N utilization efficiency were mainly controlled by additative effect; Under low N stress condition, the broad-sense heritability of NUE characters was increased while their narrow-sense heritability was decreased.2. The general combining ability of nitrogen efficiency in inbred lines 08-609 and 08-749 was high under two nitrogen levels in field, the combination 08-609 x 08-749 had super-high-yield under two nitrogen levels. Therefore, we should choose materials with high general combining ability of nitrogen use efficiency as parents to make hybrid combination in breeding eggplants with high N use efficiency.3. General combining ability and special combining ability of the root volume and plant biomass in the seedings of eggplant inbred lines were significantly different in solution condition. The variance in special combining ability of root volume and plant biomass was larger than that in general combining ability under the normal N level for 35 days, of which the inheritance was controlled by non-additive effect. While the variance in special combining ability of root volume and plant biomass was lower than that in general combining ability under the normal N level for 35 days, of which the inheritance was controlled by additive effect The broad heritability of both root volume and plant biomass are high under two nitrogen levels in solution culture condition Compared with the normal N, under the low N level the broad-sense heritability of root volume and plant biomass was the trend of decline, while their narrow-sense heritability was the trend of decrease.4. Under normal and low nitrogen stress conditions, total uptake N, nitrate reductase activity and glutamine synthetase activity in three typical eggplant genotypes with different nitrogen efficiency and their hybrids were studied under solution condition. Compared with low nitrogen efficiency genotype(08-643),the cultivars (08-609,08-749) with high N efficiency had much more total uptake N per plant, high nitrate reductase activity and glutamine synthetase activity. In three F1 hybrids F1-1 (08-643×08-609), F1-2 (08-643×08-749), and F1-3 (08-609×08-749), the Hm and Hp of nitrate reductase activity in leaves, glutamine synthetase activity in leaves and total uptake N per plant were mostly positive,in which the hybrid F1-3 displayed the best heterosis and corresponded with its yield. The results showed that the related enzymes activity of nitrogen use efficiency in eggplant seedlings may predict heterosis the early stage.
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