Studies On The Pathogens Causing Rheum Palmatum L. Root Rot

In this article, with Chinese traditional medical herb Rheum palmatum L.in Lixian county of Gansu Province.as material, Isolation and identification of the pathogens causing Rheum palmatum L. root rot, Studies on biological characteristics of the pathogen of the Rheum palmatum L. Root rot and Fungicide screen assays in lab were studied. The main results are as follows:1. The chief pathogens causing Rheum palmatum L. root rot were Thichothecium roseum (Bull.) Link., F. oxysporum schlecht., Rhizotonia solani kUhu.. The incidence of the root rot after inoculation pathogens by gore radicles were significantly higher than that by non-gore radicles. All above reveals that the wound is helpful for the root rot pathogens to infect in the plants. It suggests that the transplant and cultivation should be careful to keep the plant integrality preventing the wound.2. As T.roseum (Bull.) Link, the best carbon resources was Maltose; The best nitrogen resources was carbamide and potassium nitrate; Ultraviolet irradiation 2 houre under dark condition could promote mycelia growth, but it could restrain sporulation, light could promote mycelia for sporulation; the optimal pH was 6;The optimal temperature was 25-30℃. As F.oxysporum schlecht., sucrose was the best medium for pathogen growth, but glucose was the best medium for sporulation; sodium nitrate was the best medium for pathogen growth, but ammonium nilrate was the best medium for sporulation; Whole darkness promote mycelia growth, but ultraviolet irradiation 2 houre under dark condition could promote sporulation; The optimal pH was 6 for pathogen growth,and the optimal pH was 8 for sporulation; The optimal temperature was 25-30℃.As R.solani kUhu. the best carbon resources was Tragantine;The best nitrogen resources was ammonium nitrate; The alternation of darkness and light could restrain mycelia growth, The optimal pH was 5;The optimal temperature was 20-25℃.3. The linear result based on Logistic equation fitting mycelium growth with treatment temperatures shouwed that the pathogens causing R. palmatum L. root rot by High temperature processed 15 min,Cultivated in the condition of 25℃,No light. As T.roseum (Bull.) Link., The Growth inhibition starting temperatures were 47,60,68,67 and 68℃, LT50 were 69,79,80,83 and 83℃,Maximum inhibition rate of mycelium growth were 0.0178,0.0162,0.0149,0.0149 and 0.0120 cm/℃; As F. oxysporum schlecht., The Growth inhibition starting temperatures were 43,51,59,61 and 77℃, LT50 were 61,73,82,86 and 92℃, Maximum inhibition rate of mycelium growth were 0.0178,0.0162,0.0149,0.0149 and 0.0120 cm/℃. As R. solani kUhu.,Was sensitivity to temperatures, The Lethal temperature and time were 50℃and 15 min.4. Of 12 kinds of fungicides, there were 4 fungicides such as Zhigao, carbendazim, qiangsheng and Mancozeb had inhibition effect on the pathogens causing R. palmatum L.root rot. Their EC50 were 17.74,7.29,236.84 and 853.99 mg/L respectively to T. roseum (Bull.) Link. Their EC50 to F. oxysporum schlecht. were 56.92,1.34E-12,400.53 and 2155.04 mg/L respectively. Zhigao and carbendazim had the best and better control effects on R. solani kUhu, while the effect of Mancozeb followed.