The Infection Process Of Plasmodiophora Brassicae Wor.to Chinese Cabbage And Effect Of Boron And Silicon On This Infection

Clubroot disease is an important soil borne disease. Many scholars have got some important achievements on the life cycle of Plasmodiophora brassicae. However, there are still many problems unsolved. In the fields, stable and effective prevention methods are still lacking. This subject adopts the method of sand-nutrient solution to cultivate the Chinese cabbage and observe the infection process of Plasmodiophora brassicae by artificial inoculation. At the same time, we investigate the effect of silicon and boron on infection and pathogenesis through setting different concentrations. The research can provide theory basis to us to control Plasmodiophora brassicae by using silicon and boron. The main results are as follows:1. We adopted the method of sand-nutrient solution to cultivate the host plant and observed the development process of Plasmodiophora brassicae. The primary zoospores invade the root hair to form plasmodia or invade cortex directly after inoculated 24 hours. The plasmodia is cleavage into zoosporangia after inoculated 7 days. And then, secondary zoospores are formed in zoosporangium and released, we observed empty zoosporangia in root hair. Furthermore, we found a single sporangium-like structure after inoculated 36 hours. We observed the surface morphology by scanning electron microscopy and observed the infection process by optical microscope and paraffin section. The structure can intrude into root hair and cortex as a whole directly. we speculate that it may be another infection way of Plasmodiophora brassicae.2. We investigate the impact of boron on the occur of clubroot disease through setting different concentrations. Boron treatment have no effect on spore germination, however it can inhibite the occur of clubroot disease and reduce the incidence and disease index, indicating that the effect of boron is intracellular. In the sand culture, boron treatment can inhibite the occur of clubroot disease when the concentration is 0.2mmol/L, In the soil culture, it can reduce the incidence when the concentration is 0.4mmol/L and reduce the disease index when the concentration is 1.6mmol/L. However as the concentration of boron increasing, the host plant will show some toxicity symptom and reduce the seeding rate. In conclusion, boron treatment can inhibite the development of clubroot disease, and the best concentration is 0.4mmol/L in sand culture and 0.8mmol/L in soil culture. The difference can be explained by the soil buffer action. In addition, boron treatment can reduce the activity of POD and SOD and enhance the content of malondiadehyde in host plant, it shows that boron treatment can induce defense response mechansim and cause allergic reaction so that improve the resistance to clubroot disease.3. We investigate the impact of silicon on the occur of clubroot disease through setting different concentrations. Silicon treatment can inhibite spore germination and the infection rate of root hair. Silicon treatment can also inhibite the development of the pathogen in root hair. The incidence and disease index is highly reduced when the concentration of silicon is 1.2mmol/L. Furthermore, silicon treatment can delay the gather of dormant spore and the reasons need to be further studied.