Abstract
Accumulation and soil enrichment with non-essential heavy metals like chromium (Cr) above threshold levels results in Cr toxicity in plants. In order to study the effect of varying Cr stress levels on maize growth, photosynthesis and gas exchange capacities and yield responses, two maize hybrids i.e., Wan Dan 13 and Run Nong 35 were grown in soil contained pots contaminated with different concentrations of Cr (0 mu M, 30 mu M, 60 mu M, 90 mu M, 120 mu M and 150 mu M). Cr toxicity substantially reduced total chlorophyll contents, net photosynthesis, transpiration rate, inter-cellular CO2, stomatal conductance, water use efficiency and intrinsic water use efficiency. It further haltered growth (plant height, number of leaves/plant, leaf area, stem diameter, shoot fresh and dry weight) and yield and related attributes (ears/plant, number of kernels/row, 100-kernels weight, grain yield/plant, biological yield/plant) as well as harvest index both maize hybrids but the effects were more conspicuous in Run Nong 35 than Wan Dan 13. The overall toxicity of Cr to both maize hybrids were recorded as: 150 mu M > 120 mu M > 90 mu M > 60 mu M > 30 mu M > 0 mu M. In sum, Cr contamination negatively influenced on maize, however, Wan Dan 13 was better able to resist Cr-stress than Run Nong 35.