Abstract text: Maize lignocellulosic biomass is a promising renewable feedstock for the bio-based industry. However, this feedstock currently suffers from low processing efficiency, mainly due to the presence of lignin. Additionally, lignin negatively impacts forage digestibility for ruminants. To overcome this problem, breeding and engineering strategies have been employed to generate low-lignin maize varieties. CINNAMOYL-CoA REDUCTASE 1 (CCR1)-deficient maize plants have been shown to exhibit a reduced lignin content, increased processing efficiency, and no biomass yield penalty. Here, we further elaborated on these findings. We generated CRISPR/Cas9-mediated knock-out lines for CCR1 and its closest paralog CCR3. In greenhouse conditions, ccr1 and ccr1 ccr3 behaved similarly, showing no biomass yield penalty, comparable reductions in lignin content, and similar improvements in processing efficiency relative to controls. In field conditions, subtle differences in forage quality parameters and processing efficiency between ccr1 and ccr1 ccr3, indicated that CCR3 plays a role in lignification in field conditions, albeit a minor one. These data show that lignification in ccr1 mutants mainly depends on CCR family members other than CCR3. To investigate this further, we generated all ten triple mutant combinations of the five CCR genes present in maize via mutation-stacking, and evaluated them in a field trial.