Screening Of Brassica With Low Cadmium Accumulation

In the second national survey of wastewater irrigation, cadmium (Cd) contaminated lands accounts for 56.9% of the total land area contaminated by heavy metals. Cadmium pollution not only affects crop yield and quality, but also poses threats to human health through the food chain enrichment. Screening low Cd-accumulating cultivars provides an opportunity to produce pollution-free vegetables and secure the human health. Field experiment in Cd-contaminated vegetable field (0.97 mg Cd/kg soil) located in Zhuzhou City in Hunan Province, in combination with a hydroponic trial in greenhouse, were undertaken to select the low Cd-accumulating cultivars of Chinese cabbage(Brassica). A pot experiment was further conducted on 6 selected Chinese cabbage cultivars with different capacity to accumulate Cd (high, medium and low) in order to investigate the characteristics of Cd accumulation in plants and the responses of vegetable yield and quality to Cd presence. The main results are as follows:1) In the field experiment, shoot Cd concentrations in 34 cultivars of Brassica ranged from 0.978 to 2.416 mg/kg FW (fresh weight), and were 5 to 12 times of the national standard (GB 2762-2005).2) In the hydroponic trial, shoot Cd contents in 46 cultivars of Brassica ranged from 1.408 to 3.506 mg/kg FW at Cd level of 0.5 mg/L and from 2.352 to 6.285 mg/kg FW at Cd level of 1.0 mg/L, being respectively 7～17 and 12-31 times of the national standard (GB 2762-2005). Cultivars exhibiting desirable characteristics of low Cd and nitrate accumulation in shoots and high yield, are the tested cultivars of Beijingqinggeng, Texuanzhongaijiaoheiyebaicai, Kangresijishuikouchaotianbaicai, Youxuanchangganbai, Xiangtanaijiaobai and Taiguosijikuaicai at the level of 0.5 mg/L Cd, and ReyouNo.2, Huaguanqinggeng, Changgengbai, Beijingqinggeng, Lifengheidatou, Taiguosijikuaicai, Lvdanqinggeng and Qinggengsiji at Cd level of 1.0 mg/L.3) Based on the results of field experiment and hydroponic trial, seven cultivars could be identified as low Cd-accumulating cultivars:Kangresijishuikouchaotianbaicai, Taiguosijikuaicai, Texuanzhongaijiaoheiyebaicai, YuexiuNo.4, YuexiuNo.3, ReyouNo.2, Huaguanqinggeng, while three as high Cd-accumulating cultivars:Meidu510qinggengcai, Huainanheixinwu, Qingxin (qinggengcaiFl).4) The pot trail using three cabbage cultivars representing low, medium and high capacity in accumulating Cd showed that shoot Cd contents and accumulation amounts increased with Cd addition rates increasing. The Dose-Response function was established between shoot Cd contents and soil Cd concentrations and used for calculating the critical soil Cd concentration corresponding to the Cd threshold value in leaves vegetables (0.2 mg/kg), which was recommended by the national guidelines on safe production of vegetables. The upper limits of soil total Cd concentration were 0.514 mg/kg,0.607 mg/kg,1.000 mg/kg,0.722 mg/kg,0.544 mg/kg and 0.592 mg/kg for the safe production of YuexiuNo.4Teaibaimeigui, Hongqiaoaiqingcai, Lvlingaijiaohuang, Qingcuixiaobaicai and Beijingxinzaxiaobaicai, respectively.