| With the enlargement of cultivated area of vegetables, the trend of the cruciferous clubroot disease had been aggravating in Sichuan in recent years, which became one of the most serious problems to the production of vegetables in Sichuan. Clubroot pathogen in pakchoi root from Chengdu was used as materials in the experimentation. The resting spores of Plasmodiophora brassicae in pakchoi were distilled to study the modality and biological characteristics. The occurrence regulation of P. brassicae in pakchoi was investigated in fields, and the disease developing condition and chemical bactericidal effect were studied preliminarily in room.1 The pakchoi was inclined to be affated vegetable, which can be invaded by P. brassicae during all growth periods, especially in seedling stage. The disease damage mianly the roots, and tumours with different shape and different size would outgrowed in roots of pakchoi which invaded. The tumours in taproot are usual bigger and fewer than which in fibre. To sum up, the symptom of clubroot disease in pakchoi was considered as the typical symptom of cruciferae.2 Observing under the scanning electron microscope showed different hosts clubroot resting spores were morphological similarity and size discrepancy. The resting spores in pakchoi were nearly spherical, not slippery and mamillated on the wall of spores. Their diameters were from 1.8 to 4.2μm, and the mean of diameters was 2.8μm.3 The optimal temperature and pH for germination of resting spores of P. brassicae in pakchoi was 24℃and 6.3, respectively. The lethal temperature was 48℃. Treatment of rotted clubs was helpful to enhance the germinated rate. The visible light inhibited the germination of the resting spores. The highest germinated rate for the resting spores was 71.07% in the root exudates. The results was similar to the reports of P.brassicae in cabbage and rape.4 P. brassicae could intrude pakchoi, which cause disase in perennial. The condign time was 5～9th month, and the fastigium time was ranged from May to middle of June and from end of July to the beginning of September. Because of affect of high temperature to growth of pakchoi, diseases was decreased from end of June to the middle of July; the disease entered the slow development period from the middle of September to the beginning of November; the disease was the resting time between the middle of November to February, and restarted in March of next year. The earliest clubroot of Pakchoi was discovered in the 16th day after sowing in summer, 5 days earlier than autumn. It indicated the possibility of pathogen perniciousness depending on the temperature. The disease index of seedling in sterile soil transplanting plant was significant less than contemporaneity planted in the field.5 Compared with four inoculation techniques: dipping the root of seedlings with spore suspension, mixture of resting sopres and soil, clubroot tissue and infusion spore suspension in the rhizosphere surface, which indicate that the infusion spore suspension in the rhizosphere surface was the best inoculation approach in the room condition. The disease index reached the highest 48.23 and disease percentage reached 75.92%. The different soil types was indicated that the degree of clubroot was: paddy soil>purple soil>fluvo aquic soil, and three different soil types were extremely significant difference, The disease index reached 68.28, and the disease percentage was 88.89%, which reached highest in the paddy soil. The disease index and disease percentage was lightly increased when purple soil was added with nutrition soil or sand. Inoculation irrigated with different pH nutrient solution (pH 4～9) showed the most serious illness in pH 5, when the disease index reached the 58.73 and the disease percentage reached 81.48%.6 The spore suspension of P. brassicae in rape, cabbage and pakchoi was injected to pakchoi. The results showed no significant difference of the disease index and the disease percentage, which illustrated the similar pathogeny in pakhchoi. The spore suspension of Plasmodiophora brassicae in pakchoi was injected to three different host of rape, cabbage and pakchoi. The P. brassicae infected pakchoi was the strongest pathogenicity.7 Bactericidal effects of static cracking and perlka chemical were obvious, which average bacteriostatios ratio were 29.73% and 30.44%, respectively. They showed no significant difference for bactericidal effects, but significantly higher than cyzofamid,fluazinam and bacillus subtilis Bs2004. |
