Effects of Acyrthosiphon pisum on enzyme activities and nutrients ofdifferent alfalfa varieties

In order to investigate the biochemical mechanisms of alfalfa responses to pest aphid, the defensive enzyme activities and nutrients and their dynamic changes were studied in alfalfa varieties with different aphid resistance which were damaged by Acyrthosiphon pisum. The results showed that the activities of L-phenylalanin ammo-nialyase(PAL), superoxide dismutase (SOD), peroxidase (POD) and soluble sugar significantly increased (P0.01) within seven days of A. pisum damaged, whereas, the activities of polyphenol oxidase (PPO) and catalase (CAT) significantly declined (P0.01) in aphid resistance alfalfa varieties (Santory, MF4020, Queen, Crown, SR4030) compared with low resistance alfalfa varieties (Surprising, WL343HQ, Derby), middle resistance alfalfa varieties (Platon, Gannong No.4, Pioneer, Zhongmu No.3) are somewhere in between. The soluble protein content changed without regular pattern.