| Clubroot, caused by Plasmodiophora brassicae is a devastating soilborne disease, occurring in most of the major Chinese cabbage growing regions of China. Heavy infection by this pathogen always leads to severe economic losses of Chinese cabbage. Since effectively-resistant cultivars are still unavailable in the fields, the control of clubroot disease has now become heavily dependent on fungicides to combat.The screening model of fungicides aiming at controlling the clubroot of Chinese cabbage, the action mode of fluazinam on P. brassicae and the technology of designated-pot prevention and the methods of controlling the pathogen were studied in this paper. An integral management strategy that can be used to control the disease effectively in designated pots was put forwards simultaneously. The main research results were as follows:1. A micro-selection model of in vivo fungicides was established, which had been used to screen out 5 chemical agents inhibiting P. brassicae effectively. Inoculum was prepared as suspension of resting spores of P. brassicae origining from clubroot galls of Chinese cabbagge.Then the inoculum was added to the substrates which were composed of peat and vermiculite at the ratio of 1:10. The fugicide was mixed into the substrate 24 hours later. The seeds of Chinese cabbage were sowed into the substrates containing fugicide and the pathogens, and then kept in the solar greenhouse and shedding light on the plants at 18:00-22:00 everyday. The occurrence and severity of the disease were investigated 40 days later. Relying on the model, several fugicides that can control the pathogen P. brassicae effectively were screened out, such as pyraclostrobin, indole sulfur bacteria amine, fluazinam, chlorothalonil.2. The novel technology of detecting whether the resting spores of the Fluorescence double staining and flow cytometry was established. When treated with Hoechst 33258 at the concentration of 10μg/ml for 15 min and PI at the concentration of 5μg/ml for 5 min, the living and dead spores of P. brassicae showed blue and red fluoresence, respectively. Relying on the technology of FCM, we can quantify the numbers of living and dead spores quickly and accurately. Based on the detection technology of fluorescence double dye, it was concluded that fluoride at the concentration of 1 a.i. mg/1 had no lethal effect on spores of P. brassicae.3. The main mode of action of fluazinam inhibiting resting spore germination and vitality was preliminarily elucidated, thereby proceeding to curb the infection towards root hair, cortex and the formation of swollen roots. The inhibition ratio of fluazinam on the germination of resting spores was 94.73% at the concentration of 1 a.i. mg/1. The inhibition ratios of the vigor of resting spores were 88.56%,92.71% respectively. Forine mainly prevented P. brassicae from invading the Chinese cabbage and released therapeutic effect on the disease occuring on the seventh day.4. The progress of P. brassicae invading the root of Chinese cabbage was elucidated so as to provide theoretical basis for the control of the disease. It was more suitable to use Trypan-blue staining method to study the invading progress of P. brassicae rather than Aniline blue staining method. It was found that the pathogen can infect the root hair severely and invade the cortex slightly inoculated 4 and 7 days later. At this time, fluazinam can control the pathogen efficiently. At the 14th day of inoculation, the cortex had been infected severely and the number of secondary zoospores rised, swollen root began to form. At this time, fluazinam can’t control the pathogen.5. Pyraclostrobin was first found to that could prevent and control the pathogen P. brassicae effectively and cure the diseased plants with root hair invasion at the early stage. It was suggested that the control efficiency of pyraclostrobin (applied with water drenching and mixed into the soil respectively) were 87.50%,95.83% respectively.6. The technology of detecting the spores of P. brassicae quantitively was established, which was based on the theory of FTIR spectra. By analysing the spectra of P. brassicae, for the club roots and healthy roots of Chinese cabbage, three specific light bands of 1105,1145, 1228 cm-1 were chosen. Relying on the peak area values of the three bands, The FTIR quantitative detection model of P. brassicae was built, namely y= 34.17+12.24x1-9.81x2-6.05x3 (correlation coefficient r= 0.98, p< 0.05). The model could measure the spores quantitively and provided some reference for the detection of clubroot of Chinese cabbage theoretically.7. One percent fluazinam granules and 10% fluazinam powder were developed to prevent the clubroot of Chinese cabbage. The fluazinam granules application was quite simpe and easy in the fields. In the field experiments, fluazinam showed 41.43%control efficiency at the dosage of 6 a.i. g/667m2 in Changyang county of Hubei province in 2012. The fluazinam powder was mixed with the substrates, and then transplanted the seedlings into the prepared substrates. In the field demonstration experiments, conducted in Changyang county of Hubei province, Qingdao of Shandong, Xinye of Henan, fluazinam applied at the dosage of 10 a.i. g/667m2 showed 83.63%,71.43% and 68.56% control efficiency respectively, in 2012.8. The technology of site-specific controlling clubroot of Chinese cabbage was set up. The 12 field experiments, conducted in 3 years, proved that the fixed-point control technology could prevent the disease effectively. The progress of the technology was described as below:mix the substrates with 10% fluazinam powder, the prepared substrate wrapped in the paper-tubes or non-woven bags, sow the seeds into the paper-tubes (5 cm×7 cm) or non-woven bags (7 cm ×11 cm), transplant the seedlings into the fields 20 days later.The experiments, conducted in the greenhouse, showed that the transplant method which the seedlings were planted in the non-woven bags, could inhibit the clubroot at most and bring no harm to the seedlings. Fluazinam could exist stably in the soil, only 71.91% decomposed 102 days later. According to the experiments conducted in three places, namely Tonghai of Yunan, Xinye of Henan and Lasa of Tibet, the control efficiency of the fixed-point control technology that seedlings were nurseried in the paper-tubes and fluazinam was applied at 3 a.i. mg/1 ranged from 63.75%-70.56%in 2012-2013. In the Cabbage field trials conducted in Qingdao of Shandong, Dandong of Liaoning and Fuzhou of Fujian, the control efficiency ranged from 53.06%-75.92%. And the experiments conducted in Chengdu of Sichuan, Dandong of Liaoning and Qingdao of Shandong showed that the control efficiency of the fixed-point control technology that Chinese cabbage seedlings were nurseried in the non-woven bag and fiuazinam was applied at 10 a.i. mg/1 ranged from 81.56%-89.30% in 2014, while in the Cabbage field trials conducted in Xinye of Henan, Taibai of Shanxi and Wulong of Chongqing, the control efficiency ranged from 80.67%-87.37%.The micro-selection model of in vivo fungicides was set up to combat the severe crubroots of cruciferae crops in China. Relying on this selction model,5 fugicides that could control P. brassicae effectively were selected out. In order to detect the spores of P. brassicae live or dead, fluorescence double staining and FCM detecting technology were established. Based on the researches towards the progress of infection of P. brassicae, fixed-point control technology that conbined the paper-tubers or non-woven bags with substrates containing fugicides was established. The technology of fugicide-contained substrates combined with tube-papers or non-woven bags had made it possible that fugicide applied one time could protect crops throughout the whole growing season, with the problems of fugicide losses and environmental pollution and so on solved simultaneously. This is quite meaningful to control clubroot of cruciferae that becomes more and more severe in our country. |
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