Detection Of Soil-Born Plasmodiophora Brassicae By FQ-PCR And The Relationship Between Clubroot And Soil Characteristics And Integrated Control Technique

Clubroot, caused by Plasmodiophora brassicae Woron, is a destructive soil-borne disease on cruciferae and it is very diffcult to control due to resting spores of P. brassicae with long survival time in soil. Now the clubroot has become one of the worldwide diseases on cruciferous crops, and it also leaded seriously impact on cruciferous vegetable production in Hunan. Therefore, detection of soil-born P. brassicae by FQ-PCR, the relationship between clubroot and soil characteristics and integrated control technique were studied. The main results are as follows:1. A real-time fluorescent quantitative PCR for detecting resting spores of P. brassicae in soil sensitively and accurately was established, used PCR to amplify P. brassicae DNA with PbF/PbR primers, and restructed plasmid to construct standard curve.109 soil samples collected from Xiangshui township in Xiangtan county, Lukou town of Changsha county and Taohuajiang town of Taojiang county had been detected by FQ-PCR technique. The results showed that the resting spores in samples were between 104 to 106 resting spores/g soil, in which the crop had clubroot occurrence in field, while didn’t appear the disease symptom in which the resting spores in the field were 102 resting spores/g soil. The soil-test results were consistent with the disease symptoms in collected field. Therefore, when the resting spores in soil were more than 104 resting spores/g soil, the clubroot mostly to occurrent, must to take some appropriate measures to reduce the harm to crops.2.7 physical and chemical characteristics of 30 soil samples were detected, like resting spores of P. brassicae, pH, cation exchange capacity, total nitrogen content, total phosphor content, exchangeable Ca content and effective silicon content. Also used the samples re-planting susceptible varieties to obtain the corresponding disease indexes. The relationship between those characteristics and the occurence of cluboot was explored. The preliminary findings showed that the resting spores of P. brassicae were positively correlated with the occurrence of clubroot, the disease index of samples at the same content level changed within a certain range. The acid condition was fit for clubroot disease to break out. Soil cation exchange capacity and effective silicon content were negatively correlated with the occurrence of the clubroot, while total nitrogen content was positively correlated with it, and total phosphor content and exchangeable Ca content were not significantly correlated with the occurrence of the clubroot. Meanwhile, the pH value of soil and effective silicon content had positive correlation, they might affect the occurrence of clubroot cooperatively.3. Integrated control tecnology on clubroot was detected and applicated, include fungicides control, resistant varieties, bio-control agents and lime by field trial. In fungicides control aspects, the performances of 8 fungicides against the clubroot of Brassica campestris L.var. purpurea Bailey were evaluated. At seeding stage, the control efficacy of 4 fungicides against clubroot were above 90%, while there were 5 fungicides’ control efficacy against clubroot above 90% at adult stage, and other fungicides’ control efficacy all above 80%, they can be used to control clubroot in fieid. But 22% Azoxystrobin tebuconazole SC has phytotoxicity to crops, it can’t be used in field. In resistant varieties aspects,20 cruciferous varieties were evaluated resistant ability against clubroot. The result showed that Zigan No.2, Xiabaoganlan, Shengyouza and Xiangyouza were immune to clubroot at both seeding stage and adult stage, while other varieties also have high resistant to clubroot. And the control efficiency of lime,4% Green trichoderma viride Hartz trichoderma viride WP and Bacillus were studied, the result shows that no matter seeding stage and adult stage, the control efficiency of 4%Green trichoderma viride Hartz trichoderma viride WP were above 90%, it can be made into bio-control agents to prevent clubroot. In one word, the control efficacy against the clubroot of Brassica campestris L.var. purpurea of 81% Metalaxyl Chlorothalonil WP,75% Iprodione Carbendazim Mancozeb WP,69% Dimethomorph Mancozeb WP,75% Chlorothalonil WP and 4% Green trichoderma viride Hartz trichoderma viride WP were high and stable, they can be used to control clubroot in fieid. Zigan No.2, Xiabaoganlan, Shengyouza and Xiangyouza were immune to clubroot, they can be planted in infected area.