The Occurrence And Epidemic Condition Of Rape Clubroot Disease Caused By Plasmodiophora Brassicae

Clubroot caused by Plasmodiophora brassicae Wor., is one of the most serious plant diseases all over the world. P. brassicae is mainly infected with cruciferous plants, harming plant roots, stimulating root cells to form tumors, then suffocating the function of absorbing water and nutrients. When the disease is severe, roots rot and even the whole plant dead. If the field is infected by P. brassicae, the soil will be carried P. Brassicae for a long time and be no longer suitable to cultivate cruciferous crops. In recent years, the area of the cruciferous clubroot disease has been broadened; the degree of causing diseases has been increased as well as the prevention of disease be difficult year by year in our country. It had been seriously threated to rapeseed production in Anhui Province. To understand the occurrence characteristics of rape clubroot, further clarifying the occurrence conditions of rape clubroot disease, effective control the hazards of clubroot. By the method of mixing resting spores of the pathogen with soil, some factors like soil pH, soil moisture, club rot treatment, inoculums concentration, calcium application, nitrogen fertilizer application, photoperiod and temperature were studied in indoor pot experiment,respectively. The main results were as follows:1. Impact of soil pH and soil moisture on the disease incidenceResults indicated that rape plants were able to contract the disease under soil pH from 4 to 7. The disease incidence and disease index were the highest when pH was 5, were significant difference with that of others. Under pH was 8 or 9, the plants were healthy. The results explained that alkaline environment can inhibit the occurrence of clubroot disease. The plants might not cause diseases when soil moisture content was about 20%, the disease incidence and disease index gradually increased when the soil moisture increased from 30% to 50%, the disease was serious when soil moisture content was about 60%. When the soil moisture increased to 70% or 80%, the disease incidence and disease index were slightly reduced. The soil pH, soil moisture were significant correlation with the occurrence of clubroot.2. Impact of club rot treatment and inoculums concentration on the disease incidenceThe disease incidence and disease index with club rot treatment were higher than that of no rotted treatment, it explained that club rot treatment can promote the germination of resting spores, was in favor of enlarging the the disease incidence and disease index. Under the inoculums concentration from 104 to 107 resting spores/mL, the higher the inoculums concentration, the higher the disease incidence and disease index. The host might not diseased when the inoculums concentration was less than 104 resting spores/mL. The inoculums concentration of resting spores was significant correlation with the occurrence of clubroot.3. Impact of calcium application and nitrogen fertilizer application on the disease incidenceWith different concentrations of CaCl2 solution watering plants, the disease incidence and disease index were significantly lower than that of the plants watered with tap water. With the increase of calcium ion concentration, the disease incidence and disease index were reduced. It explained that increasing the calcium content of the soil can effectively suppress clubroot. Comparing with non-nitrogen, increase of nitrogen fertilizer application promoted the occurrence of clubroot. At the level of nitrogen from 11 to 21g/m2, the more nitrogen, the more serious the disease incidence and disease index. When the nitrogen application was higher than 21 g/m2, the incidence of clubroot was lower, but still significantly higher than that of the non-nitrogen group.4. Impact of photoperiod and temperature on the root hairs infectionThe root hairs infection affected by photoperiod and temperature. Photoperiod within 6-21 h/d, the root hairs infection rate as the illumination time extended showed a tendency of middle high two head low. The lowest infection rate of root hairs when photoperiod was 6h/d, the root hairs infection was the most serious when 21 h/d. At the temperature of 10-25℃, the higher the temperature, the more serious the root hairs infection. It explained that low temperature can suppress P. Brassicae infection on the plant root hairs. The photoperiod and temperature were significant correlation with the root hairs infection.