Development of lucerne root morphology traits in lucerne-grass mixture in relation to forage yield and root disease score

•Lucerne root branching corresponded better with lucerne plant density than by grass sowing ratio.•Grasses in mixture caused lucerne to form its root branches deeper than in monoculture.•Lucerne stem density was the best predictor of lucerne dry matter yield in the mixture.•Root potential index could be a effective indicator for lucerne performance in mixture.