Difference Of Nitrate Content Between Genotypes Of Pak-choi And It's Genetic Behavior

Vegetable is an important non-staple foodstuff in our daily life. It provides vitamins, minerals and fibers to us good and cheap. However, it also accumulates nitrate when it grows in the field, and may imperil our health seriously. It was suggested that more attention should be paid on this problem. The following measures should be demonstrated nowadays in decreasing the content of nitrate in vegetables. They are the reasonable application of nitrogen fertilizer, the betterment of ecological environment, the preference of picking time, the expediential of storage, process and pre-table treatment, etc. But the contamination of vegetables especial leaf vegetables by nitrate was more serious with the increasing nitrogen fertilizer application.The differences on nitrate content between vegetable cultivars were first pointed out by Cantliffe in 1972. These differences offer good prospects for breeding for low nitrate content vegetable cultivars as the desired characteristic. Pak-choi, a favor and year round supplied vegetable in south China, was used as material to study the differences of nitrate content between genotypes in this paper. The research focused on the genotype variation of nitrate content and its mechanism in pak-choi in order to provide theoretical and technical instructions to reduce the content of nitrate in pak-choi. The main result are as fellows: 1 The genotypic differences of nitrate content in 46 pak-choi cultivars were studied during winter of 1998 and spring, summer, autumn of 1999.The results showed that there were significant differences of nitrate content among different cultivars of pak-choi. The cultivars of high and low nitrate content have been screened by the cluster analysis based onthe experiment of four season .The lowest nitrate content pak-choi cultivars were: "Shanghai Qing", "Aijiao Nai Baicai" , "Hongming Qing", "Reyou 2".They were all get lowest nitrate content in different seasons. The result also showed that the nitrate content of the same cultivar in different seasons were different. The nitrate content in spring and summer were higher than in autumn and winter. No correlation was observed between the yield of per plant and the content of nitrate in pak-choi in these studies.2 The effect of different amount of nitrogen fertilizer applied (0, 25, 50, 100 kg urea/667m2) on yield and nitrate content of different pak-choi cultivars was observed . Significant differences were found between the different amount of nitrogen applied and between the different pak-choi cultivars. The result showed that the yield and content of nitrate in all tested pak-choi cultivars (both high nitrate content and low nitrate content cultivars) were increased with the increasing of the amount of nitrogen applied. The another experiment was carried out in order to research the effects of nitrogen concentration of nutrient solution on yield and nitrate content of hydroponically growth pak-choi. The results also showed the nitrate content of tested pak-choi cultivars (both high nitrate content and low nitrate content cultivars) were sharply increased as the increasing of N concentration in the nutrient solution. Significant differences of nitrate content in pak-choi between cultivars were also observed in both experiment at lower N supply, they are 25, 50kg/667m2 in soil culture and 6, 12mmol/l in solution culture. However, No difference between cultivars were observed at higher N supply (100kg urea /667m2 in soil and 18mmol/i N in solution). However no significant correlation between the yield and the content of nitrate in pak-choi was observed in both soil culture test and nutrient solution culture test.3 Nitrate uptake rate and NRA (nitrate reductase activity) were measured for explaining genotypic differences of nitrate content in Pak-choi. Results showed that the rate of nitrate uptake and NRA differed significantly in different pak-choi cultivars. It was concluded that the genotypic differences of nitrate content in pak-choi resulted fromdiffere...