Induced Resistance In Safflower Against Safflower Rust Disease By Exogenous Chemicals

Safflower was a important medicinal plant.The safflower rust caused by Puccinia carthami Corda was the most destructive foliar disease of safflower in recent years. Effects of 5 exogenous chemical compounds on induced resistance to Puccinia carthami Corda and physiological mechanism induced by salicylates (SA) were studied systemically, the purpose is that get the basis to prevent and control this plant disease. The results were as follows :Measurement of conidial germination of Uredospores showed that within certain concentrations these chemicals had no significant influence on Uredospores germination and also have no significant influence on the growth of the safflower.These inducer candidates were safe to safflower.The induced resistance was detected after safflower being treated with these inducers and inoculated with Uredospores.Results showed that 4 chemicals were effective to induce resistance. Several of them greatly reduced the disease caused by Puccinia carthami Corda. and could be good inducers. Among them, SA was the most effective and reduced disease severity, relative to controls, by up to 39.5% and the effects of Oxalic acid, Vitamin K₃, were 21.2%,31.2%, respectively.Furthermore, growth stage of plant was another important factor for efficiency of induction. The induction resistance was more effective at seedling stage than at Jointing stage.Dose of inducer was significant for efficiency of induced resistance. Efficacy of SA increase with the applied concentration.And so was it with Oxalic acid and Vitamin K₃ with certain concentrations, but the efficacy decreased with high doses. When the leaves were treated with 5.0mmol/L Oxalic acid or 2 mmol/L Vitamin K3 would also lead to reduce of disease severity, the effects were 21.2%, 31.2%, respectively.The optimum concentration of SA treatment to induce resistance of maize seedlings was 4mmol/L, which showed requirement of induction with Relative high concentration of SA from Uredospores.The highest level of induced resistance was acquired when safflower leaves were sprayed with 4mmol/L SA and inoculated with fungal spore suspension two days later. In SA-treated safflower seedlings, induced resistance was demonstrated to be lasted for 10-12 days. Defence enzymes PPO, POD, PAL and CAT played important roles in induced resistance to Puccinia carthami(Hutz)Corda. SA treatment dramatically increased relative activity of these enzymes. The activity of some of them increased transiently soon after induction, most of them only increased remarkably after inoculation. The content of Malonaldehyde (MDA) was declined along with the day after treating with SA.Therefore, the remarkable increase of the enzyme in plants treated with SA and then inoculated with Uredospores, which evidently revealed that the decrease in disease severity following treatment with these agents was a result of resistance induction. Furthermore, when the first and second leaves were sprayed with 4mmol/L SA, activity of the defence enzymes was increased on the third and fourth leaves to CK. And disease index also decreased. Results showed that resistance of safflower by exogenous chemicals were typically a systemic acquired resistance (SAR) characterized by systemicity and durability.