Alfalfa Autotoxicity: Role of Cultivar Renovation in Mitigating Germination and Seedling Growth under Continuous Cropping Systems

Background: Alfalfa often fails in continuous cropping due to its autotoxicity effect. Rotation is considered an effective way to mitigate autotoxicity; however, crop rotation is typically practiced between alfalfa and non-leguminous crops rather than among different alfalfa varieties. Therefore, understanding the germination and seedling growth of alfalfa after continuous cropping is of great significance to reveal the possibility of continuous cropping of alfalfa. Methods: The leaves of alfalfa (Medicago sativa L. cv ZhongMu No.1) were collected to determine the seed germination rate, germination potential, germination index, vigor index, seedling growth and physiological characteristics, including malondialdehyde (MDA), soluble sugar (SS), soluble protein (SP), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), in four alfalfa varieties (XunLu, GongNong No.1, ZhongMu No.1 and JuNeng 995). Result: The germination rate, germination potential, germination index and vigor index of the four alfalfa varieties decreased with increasing concentrations of leaf extract from ZhongMu No.1. JuNeng 995 exhibited better germination conditions than the other three varieties. Similarly, JuNeng 995 demonstrated superior plant length compared to the other varieties. The alfalfa cultivar, extract concentration and their interaction significantly influenced MDA, SS, SP, CAT and POD levels. However, these effects varied inconsistently with respect to extract concentration or variety. Furthermore, while the extract inhibited germination and vigor, it promoted seedling elongation in the remaining plants. GI was found to be negatively correlated with seedling length. Conclusively, the continuous cropping barrier effect of alfalfa became more severe with increasing extract concentrations. Cultivar renovation was identified as a potentially effective strategy to reduce the autotoxicity of alfalfa in this study.