β-actin was used as internal standard. All primers were synthesized commercially by TaKaRa Biotechnology (Dalian, China). Quantitative Real-time PCR used was 96-well CFX-96 Real-Time PCR detection System (Bio-Rad, USA). The SYBR Green PCR reaction system was 10 μl in total, it was composed of 5 μl SYBR Premix Ex Taq™ (2×), 1 μl each of forward and reverse primers, 2 μl ddH2O and 1 μl cDNA. Each sample was amplified in triplicate. The parameters of real-time PCR were as follows: a pre-run at 95 °C for 10 s, 40 cycles of denaturation step at 95 °C for 5 s, followed by a 60 °C annealing step for 25 s and a 72 °C extension step for 15 s. Melting curve conditions were: 1 cycle of denaturation at 95 °C for 10 s, then 65 °C change to 95 °C with temperature change velocity at 0.5 °C/s. Gene expression data from replicate samples were averaged and analyzed using the Pfaffl method (Pfaffl, 2001) to between the cassava and maize cycle threshold values.