Symptoms mainly affect the roots of rape, root or lateral root enlargement into a spindle-shaped or finger-shaped to irregular tumors, after the epidermis becomes dark and rough, poor growth in the ground, causing the leaves yellow wilting.
The pathogen Plasmodiophora brassicae Woron is called Plasmodiophora brassicae Woron. The resting sporangia are formed in host cells, spherical or ovate, thin walls, colorless, unit cells, size 4.6-6.01.6-4.6 (μm), and produce zoospores by germination. The zoospore-shaped pear or spherical, 2.5-3.5μm in diameter, with two flagellums of varying lengths in the front, which can swim in water and become deformed after resting, invade the host cells from the root hairs of rapeseed and go through a series of evolutions. And expansion, from the root cortex to the formation layer, stimulate the host parenchyma cells to divide, expand, cause the root system to form tumors, and finally the bacteria form a large number of dormant sporangia in the host cells. After the tumor rots, the large vesicles of dormant spores enter the soil in winter. .
Transmission routes and pathogenic conditions The pathogens live in the soil with their dormant cysts or adhere to the seeds and survive in the soil for 10-15 years. The sporangia are transmitted by rain, irrigation water, pests, and agricultural operations. The spores invade the host by germination. After about 10 days, the roots produce tumors. The bacteria can be developed at 9-30°C, and the optimum temperature is 23°C. Suitable relative humidity 50%-98%. Soil moisture below 45% died of germs. Suitable for pH6.2, less than the incidence of pH7.2 or less. General low-lying and water changes into dry fields or after CaO deficiency.
Prevention and control methods (1) Apply rotation for more than 3 years to avoid rapeseed growing on low-lying plots of water or rice, wheat, or rapeseed fields or on acidic soils. (2) Seedlings transplanted in rapeseed are planted with disease-free soil or formalin or pentachloronitrobenzene is used to sterilize the seedbed. The method refers to damping-off. (3) To improve the soil and apply slaked lime 100-150kg per 667m2 in acid soil, and add organic fertilizer. (4) Strengthen the cultivation and management, remove the stagnant water in the field, remove the diseased plants and burn them out of the field, and remove the lime around the diseased points to prevent the spread of germs. (5) If necessary, use 40% pentachloronitrobenzene powder 500 times suspension to root, 0.4-0.5L per plant, or 667m2 use 40% pentachloronitrobenzene 2-3kg and 40-50kg fine soil. The ditch was applied to the planting point before planting rape.
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