Application of multiwall carbon nanotubes (MWCNTs) could have promotive effects on crop plants; however, their effects on seed germination and early growth of maize under cadmium (Cd) stress have rarely been investigated. A pot experiment was conducted with two maize varieties, Yuebaitiannuo7 and Yuecainuo2, grown under three Cd levels, i.e., 0, 100, and 200 mg L−1 (denoted as Cd0, Cd100, and Cd200, respectively) and three MWCNT levels, i.e., 0, 100, and 200 mg L−1 (denoted as M0, M100, and M200, respectively) as seed priming treatments to assess the MWCNT-induced modulations in seed germination rate, seedling growth, and related physio-biochemical attributes under Cd stress. Yuebaitiannuo7 showed higher seed germination rate and less root and shoot growth than Yuecainuo2. The MWCNT application promoted the seed germination rate of Yuecainuo2 by 11.42% at M100 and 24.76% at M200 under Cd100 at 4 days after sowing; however, these effects remained non-significant for Yuebaitiannuo7. Moreover, the MWCNTs enhanced root and shoot fresh weight and antioxidant enzyme activities, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities, and reduced the malonaldehyde (MDA) content under Cd across MWCNT treatments. Nevertheless, the toxic effects were also observed, indicating a potential risk posed by MWCNTs at high concentrations. Application of MWCNTs alleviated the Cd toxicity in growing maize plants; however, their effects were concentration dependent. Yuecainuo2 performed better than Yuebaitiannuo7 with the application of MWCNT under Cd stress.
