Taizishen′s Resistance to Leaf Spot Disease Induced by Salicylic Acid

Salicylic acid(SA) was applied on Taizishen(Pseudostellaria heterophylla) to induce the plant's resistance to the leaf spot disease.Enzyme activities relating to the disease-resistance were investigated.In vitro-regenerated Taizishen plantlets were treated under aseptic conditions with 6 different concentrations of SA,0.5-15 mmol·L-1,to determine the optimum SA induction level.Activities of various enzymes in the leaves were determined within 1-7 days after SA treatment.The disease-resistance of the treated plantlets was observed with the application of a water suspension of the leaf spot spores,7 days after the treatment.The results showed that(a) the activity of the enzymes,such as peroxidase and polyphenol oxidase,in the leaves was enhanced by SA treatment;(b) the catalase activity was significantly inhibited after induction by SA at a concentration of 5 mmol·L-1;and(c) POD activity increased by 170%,PPO increased by 293%,and CAT decreased by 43.3%,as compared to the control.SA concentration in the range of 0.5-15 mmol·L-1 appeared to be capable of inducing the disease-resistance in Taizishen.The best result seemed to be at the concentration of 5 mmol·L-1 SA,as the average effective rate was 59.6%,which was significantly higher than those achieved by the other treatments.