Study On Composite Cold Resistance Agent Of Maize Seedlings

Maize is a kind of thermophilic crops which is more sensitive to low temperature. The usage of cold resistance agent is an important measure to improve its cold resistance when faced with disasters of low temperature. However, most of the cold resistant agents have the problem that the cold resistance effect is not significant, reagents residue has many side effects or brings severe environmental pollution. Therefore, developing a suitable composite cold resistant agent which has small dosage, good effect and safety guarantee for maize has important practical significance. On the basis of the known single non-toxic cold resistant agent, the paper chooses maize seedlings as the experimental materials and simulates low-temperature stress in the laboratory. We Preprocess the maize seedlings using foliar spray of Salicylic Acid(SA), Abscisic Acid(ABA), Ascorbic Acid(ASA), Fulvic Acid(FA),Potassium Phosphate Monobasic(KH2PO4), Chitosan(CTS)and Locust Bean Gum(LBG), and measure the relevant growth and physiological indexes of maize seedlings which had been treated with low temperature. Then we select three single excellent cold resistant agents----SA, ABA and FA, to make into composite cold resistant agent added by appropriate concentration of CTS which is film forming agent. BOX-Behnken Design in response surface methodology is used to screen and optimize the optimal concentration ratio composite cold resistant agent by projecting different factors and levels. And then this thesis studies the mechanism of cold resistant agent for maize seedlings according to the test of physiological and biochemical indexes such as the level of membrane lipid peroxidation, antioxidant enzyme activity, soluble protein content, soluble sugar and free proline of different varieties of maize seedlings. The methodology by which complex formulation of SA, ABA, FA and basic film forming agent is used, provided technology support for the application and popularization of new composite cold resistant agent.The main work is as follows:1.Compared with the control of water treatment at low temperature, preprocessed maize seedlings by SA, ABA, ASA, FA, KH2PO4, CTS and LBG has lower relative electrical conductivity and MDA content, while enhances SOD activity, soluble protein content,relative growth rate,and dry matter accumulation rate as well. Meanwhile, different cold resistant agents had different effects on the chilling tolerance for the same maize seedlings. Among all the treatments of maize seedlings, pretreatment with SA had excellent cold hardiness, followed by ABA and FA. Comprehensive analysis of various growth and physiological indexes indicates that the chilling tolerance of various cold resistant agent for maize seedling is as follows: SA(0.14g/L), ABA(0.02g/L),FA(0.6g/L),KH2PO4(3.0g/L),ASA(3.0g/L),CTS(0.25g/L) and LBG(0.25g/L).2. By response surface methodology and using CTS as the basic film forming agent,we screen and optimize the optimal concentration ratio composite cold resistant agent from the composite cold resistant agents which formed of CTS, SA, ABA and FA, and find that the best compound ratio is 0.14 g/L SA+0.021g/L ABA+0.72g/L FA. Meanwhile, at low temperature, the interaction of different cold resistant materials have different effects on various indexes. All in all, interaction of SA and FA has the most significant effect. Experiment results show that the pretreatment of composite cold resistant agent is better than single cold resistant agents or supplied by market.3. Four different varieties of maize seedlings of Yuyu 22,Xianyu 335, Jinsui1203 and Ganyu 801 are used to study the physiological mechanism of chilling tolerance and how the composite cold resistant agent could improve maize seedlings' cold resistance. By monitoring different physiological and biochemical indexes, we found that the pretreatment via composite cold resistant agents can generally improve the cold resistance of maize seedlings. However different varieties have their own situations. The relative electrical conductivity, MDA content and generation rate of O2- show a lower level before the low temperature stress, while higher SOD,CAT and POD activity, soluble protein content, soluble sugars and free proline content is observed during the whole process. Otherwise has a lower chilling tolerance. Overall the best effect of composite cold resistant agents is Ganyu 801,while Xianyu 335 has lowest response.That means that different varieties of maize has different response to composite cold resistant agents, so which have different levels of chilling tolerance after the application of cold resistant agents.