Pathogenic Effect And Control Research Of Plasmodiophora Brassicae In Rape

The bioassay, component, pathogenicity of toxic extraction and characteristic of growh and defensive enzyme activities in rape were studied preliminarily in this paper. Though field plot efficacy trial and field demonstration experiment, control effects of five biological pesticides against rape clubroot disease and the best reagent treatment method of cyazofamid was studied. The results were as follows:(1)The bioactivity determination and component analysis of crude toxin produced by Plasmodiophora brassicae was studied. The result showed that the crude toxin could inhibit radicle growth and cause wilt symptoms on the seeding, and the toxic effect on the seedings was enhanced with the increase of the toxin concentration and the treatment time. The content of the protein and glucose of toxin was measured by coomassie brilliant blue G-250 method and anthrone colorimetry. The analysis indicated that the protein content was 329.536μg?m L-1,the glucose content was 422.762μg?m L-1。(2)Pathogenic identification of Plasmodiophora brassicae crude toxin showed that the electrical conductivity and MDA content of rape leaves displayed ascending trend, among them, the MDA content of 80% and 100% crude toxin reached their peak value at 72 h, with their contents were 2.34 and 2.66 times of control. In addition, chlorophyll a, b content and root activity in leaves exhibited a significant decrease, especially chlorophyll a reduced greatly.(3)The determination of defense enzyme activities and growh indexes of rape showed that the activities of POD, SOD and PPO in the treated rape leaves were all increased at different degrees and the enzyme activities firstly enhanced, then decreased after treated by high concentration toxin.The activity of POD reached its highest value at 48 h and was 4.2 times of the control. Activities of SOD and PPO reached their maximal level at 72 h, with their activities were 1.83 and 7.00 times of control. Activities of CAT and PAL decreased at the beginning then increased, activity of both enzymes reached their peak at 72 h, with their activities were 3.52 and 6.75 times of control. The seedling height, root length, dry weights of upperground parts and roots of rape all appeared the gradually decreasing trend with rising of crude toxin concentration.(4)The results of screening for efficient biological pesticides in fields showed that,the control efficacy of these biological pesticides had better effect than the control, with rate ranged from 16.2% to 66.2%. The order of the effect at seedling stage was cyazofamid > trichoderma harzianum > trichoderma viride >shenqinmycin > pseudomonas fluorescens > bacillus subtilis. The order of the effect at bolting stage was shenqinmycin > cyazofamid > trichoderma harzianum > pseudomonas fluorescens > trichoderma viride > bacillus subtilis. The order of the yield-increasing effect was cyazofamid > shenqinmycin > trichoderma harzianum > pseudomonas fluorescens > trichoderma viride > bacillus subtilis.(5)The efficacy experiment on field showed that root soaking, root pouring, seed dressing of cyazofamid got a certain effect on rape clubroot disease prevention. The effect at seedling stage was seed dressing > root pouring > root soaking. The effect at bolting stage was root soaking > seed dressing > root pouring. The converted unit yield was root soaking > root pouring > seed dressing.