The Influence Of Soil Moisture Content,pH, Ca²⁺ Concentration To Plasmodiophora Brassicae Infection And Disease Occur

Clubroot disease is an important soil borne diseases on vegetables, seriously affect the cruciferae vegetables yield and quality, has a close relationship with the pathogenicity of pathogen, the resistance of host and the external environment condition. So far, the production lack of effective and stable control means, and healthy soil management is an important way to prevent disease occurs. Based on the dominant No.4race of Hubei province and the common susceptible Chinese cabbage variety, this study set a range of different environmental conditions (soil moisture content, pH, concentration of Ca2+) gradient processings, analyze their influence to pathogen early infection and late onset, provide references for agriculture control. Moreover, in view of the soil nutrients Ca2+on the significant role of inhibition disease, analyze the changes of the host metabolism under different Ca2+concentrations, in order to further explore the physiological mechanism of Ca2+to improve the host disease resistance. The main research results are as follows:1. Effcets of soil moisture content on Plasmodiophora brassicae infection and disease occurs. Plasmodiophora brassicae infection rate is after first increased fast, the treatments of60%and70%are the fastest, the first days after germination is detected significantly; The root hair infection percentage is after rising first down, the treatments of70%is the highest; Incidence and disease index are after rising first down, the60%soil moisture content is the highest, below or equal to50%treatments are relatively low. Therefore, the suitable high soil moisture content can further improve the disease by acting on the pathogen development process like zoospore dispersion, root hair and cortex infection, Low or too high soil moisture content may interfere with this process to reduce disease occurs.2. Effcets of pH on Plasmodiophora brassicae infection and disease occurs. Strong acidic and alkaline conditions may inhibit resting spore germination; Plasmodiophora brassicae infection speed is high when acid and low when alkaline; Alkaline condition can interfere and delay the pathogen life cycle, make primary plasmodium become deformed and condense into globular, the primary plasmodium can’t divide properly or delay forming a zoosporangium; Incidence and disease index are after rising first down, the treatment of pH5.0is the highest. Although the incidence and disease index are zero when pH8.0, this condition can interfere with the root and upside of the plant. The incidence is low and the plant can healthily grow when pH7.0. So, the suitable low pH can improve the disease by acting on the pathogen life cycle like resting spore germination, root hair and cortex infection, neutral or alkaline conditions may interfere with this process to reduce disease occurs.3. Effects of pH and Ca+concentrations on Plasmodiophora brassicae infection and disease occurs. Suitable high concentration of Ca2+can inhibit the spore germination, delay the pathogen life cycle, reduce the degree of the disease occurs, incidence and disease index are after rising first down, highsets at2.5mM Ca2+concentration, relative high at7.5mM, the completion of the pathogen life cycle depends on a small amount of Ca2+to a certain extent under acidic and neutral condition, that means it can reduce the disease occurs by interfering with rest spore germination and life cycle. Suitable high concentration of Ca2+can further reduce the happenings of the disease, the falling range is the biggest, and the plant can grow healthily. Resting spore germinaton and root hair infection rate is low under alkaline condition, the life cycle is significantly delayed, no disease occurs. High concentration of Ca+can reduce the disease occurs, pH plays a leading role, Ca2+effection is obvious when acidity, relative obvious when neutral, not obvious when alkalinity. The role of the two factors has certain independence, also has certain restriction and promotion.4. The physiological and biochemical mechanism of high Ca2+concentration to improve the host resistance. Plasmodiophora brassicae can enhance the function (adsorption and secondary infecetion) of promoting the dry weight accumulation at suitable high Ca2+concentration (5mM) or weaken the function of inhibiting the dry weight accumulation; The pathogen can stimulate the increase of root activity in adsorption and secondary infection phase, Ca2+can weaken the pathogen role of inhibiting root activity in root hair infection, root activity variation is basically identical as the tread of dry weight accumulation, pathogen may act on root activity to influence the dry weight accumulation. In addition, Plasmodiophora brassicae can promote the accumulation of pro line at suitable high Ca2+concentration (7.5mM), weaken root membrane lipid peroxidation (7.5mM,15mM), then enhance the host resistance. As a consequence, Ca2+play a role of enhancing the host resistance by influencing root activity, proline accumulation and membrane lipid peroxidation.