Abstract:

In this study， we explored the responses of five new alfalfa （Medicago sativa） lines （P₁， P₂， P₃， P₄， and P₅） and M. sativa cv. ‘Zhongmu’ No.1 （ZM） to salt stress. The morphological and physiological parameters of alfalfa in the early flowering stage were measured at 0 （CK）， 8， and 20 days under salt stress （200?mmol·L^-1 NaCl）. The results show that with the extension of salt stress， there was increasing inhibition of plant height， leaf area， aboveground biomass， underground biomass， and K⁺ content of aboveground and underground parts of alfalfa plants. Salt stress also inhibited the growth of the root system of alfalfa plants， with negative effects on the total root length， total root surface area， average root diameter， root volume， and root tip number. The total flavonoid content and the activities of phenylalanine ammonia-lyase， cinnamic acid-4-hydroxylase， and 4-coumarate-coenzyme A ligase were increased under salt stress， as were the Na⁺ contents in the aboveground and underground parts. Principal component analysis revealed that underground K⁺ and Na⁺ contents， root tip number， plant height， and leaf area are the preferred indices for evaluating the salt tolerance of alfalfa at the early flowering stage. On the basis of a comprehensive evaluation with the membership function method， the M. sativa lines were ranked from most to least salt tolerant as follows： P₃>P₄>P₅>ZM>P₂>P₁. These findings provide a theoretical basis for breeding new salt-resistant alfalfa cultivars.

Key words: alfalfa, salt tolerance, flavones, phenylalanine ammonia-lyase