Effects of cadmium-zinc compound stress on seed germination characteristics of different alfalfa varieties

This study aimed to compare the effects of cadmium-zinc compound stress on seed germination and seedlings of different alfalfa varieties alongside the tolerance of different alfalfa varieties to cadmium-zinc stress. For this, alfalfa seeds were treated with Cd-Zn solution (Cd²⁺ concentrations: 0, 5, 10, 50, 100, and 200 mg·L⁻¹; Zn²⁺ concentration: 50 mg·L⁻¹). Subsequently, the germination potential, germination rate, germination index, radicle length, and plumule length were calculated. Furthermore, the membership function method for alfalfa provided a comprehensive analysis of the Cd-Zn tolerance. The results showed that Cd-Zn treatments had varying effects on the germination potential, germination rate, germination index, radicle length, and plumule length. With increasing Cd-Zn concentration, the germination potential, germination rate, germination index, radicle length, and plumule length of ‘Zhongcao No.3’, ‘Magnum 2’, and ‘Millionaire’ all initially increased before decreasing. Meanwhile, the radicle and plumule lengths of ‘Caoyuan No.3’, ‘SK3010’, ‘Baimu 202’, ‘WL363HQ’, ‘Millionaire’, ‘Zhonglan No.2’, and ‘Magnum 2’ all decreased. Additionally, 200 mg·L⁻¹ Cd²⁺ and 50 mg·L⁻¹ Zn²⁺ concentrations had inhibitory effects on the germination of different alfalfa seeds. The Cd-Zn resistance of alfalfa during germination was as follows: ‘Caoyuan No.3’ > ‘Zhongcao No.3’ > ‘SK3010’ > ‘Baimu 202’ > ‘WL363HQ’ > ‘Millionaire’ > ‘Zhonglan No.2’ > ‘Magnum 2’. Through cluster analysis, the Cd-Zn resistance of eight alfalfa varieties could be divided into three categories: strong Cd-Zn resistance, moderate Cd-Zn resistance, and weak Cd-Zn resistance.