Use Of Genetic Variability And Mineral Nutrition To Minimize Cadmium Accumulation In Wheat

Cadmium is toxic heavy metal soil pollutant and contamination of plant-based foods accounts for at least 70 % of Cd intake by humans. Cultivating low-Cd plant species and optimum application of zinc (Zn) and silicon (Si) nutrients was hypothesized as a possible solution to avoid Cd intake.The research project is comprised of six separate experiments focusing on four major issues: i) identification of variation in Cd accumulation and tolerance among wheat cultivars under cultivation in Pakistan; ii) evaluating root zone acidification and antioxidants response of low and high Cd accumulating wheat cultivars to Cd stress; iii) underpinning the mechanism by which silicon could lower Cd in plants and optimizing its rate of application; and iv) determining the effect of combined Zn and Si application on Cd concentration in wheat grains. Considerable variation in shoot and root Cd concentration was observed among the wheat cultivars that was found to be regulated by differences in both absorption by roots and translocation to shoots. Decrease in root zone pH was not related to shoot Cd concentration of the cultivars and Cd concentration in low-shoot-Cd cultivars was related to sustained or higher activity of antioxidant enzymes which was not observed for high-shoot-Cd cultivars. Higher retention of Cd in roots of both low and high Cd accumulating cultivars while decrease in excessive transpiration only in HSCd cultivars with Si application proved to be the mechanisms suppressing Cd translocation to shoots. Higher increase in antioxidant activity with corresponding higher decrease in shoot Cd concentration in low-shoot-Cd cultivars suggested that improvement in antioxidant activity was associated with lowering Cd concentration in tissue. In soil, Si decreased Cd concentration in wheat cultivars by both decrease in plant available soil Cd and its translocation from roots to shoots. Moreover, application of Si at 150 mg kg-1 proved to be the optimum level of Si that significantly lowered Cd concentration in wheat grains. The combined application of Zn and Si decreased Cd concentration in soil and consequently in grains and straw of wheat cultivars without affecting Zn concentration in grain and straw. Zinc decreased grain Cd concentration by lowering its translocation from shoot to grain and was depending on Zn uptake and translocation efficiency of wheat cultivars. Silicon induced improvement in grain yield and decline in Cd concentration was higher for salt-affected than normal soil and also for salt-sensitive compared to -tolerant wheat cultivars.