| Shandong Province, which has bigger plant area of peanut, is the biggest produce and export base of peanut in China. In recent years, peanut collar rot was more and more serious in the main producing areas of peanut, caused considerable economic losses in Shandong Province. According to the survey, we found that peanut seedings and older plants including pods are subject to attack. The rate of diseased plant was 5% to 10% in the field on average,in the serious diseased field,which was more than 50%.So the disease has been one of the serious diseases in peanut culture in Shandong Province, seriously influenced the output and quality. In order to find out pathogens and control the diseases,the following aspects were studied in this thesis:1. During 2007 to 2008, seedings and mature plants of diseased peanut were collected from thirteen counties in Shandong Province. The result of isolation showed that the disease was mainly caused by Diplodia sp.. Six isolates from different location were selected from isolates for pathogenicity tests.The symptom developed on the inoculated plants was consistent with that in field.And the same pathogen was consistently re-isolated from infected plants. According to its characteristics of morphology and sequence analysis of the internal transcribed spacer region of the ribosomal DNA (ITS), the pathogen causing peanut collar rot in Shandong province was identified as Diplodia gossypina (synonyms Lasiodiplodia theobromae and Botryodiplodia theobromae).2. The study of pathogen's biological characterizeation showed that the optimum medium is PDA, the optimum pH was 4.0-8.0,the optimum temperature was 28-30℃for mycelial growth, the pathogen can grow and turn pink at 35℃on PDA.Different lighting time had no significant effect on mycelial growth, but The pathogen produced pycnidium more quickly under the condition of continuous fluorescent light.The lethal temperature of the mycelium was 52℃for 10 min.3. Five inoculation techniques of peanut on D. gossypina were tested in greenhouse.The results showed that the toothpick technique were the most effective methods to inoculate peanut in greenhouse for resistance evaluation. The resistance test on fourteen peanut cultivars performed by the toothpick technique in greenhouse for its reliable and easy. It showed that almostly all peanut cultivars were susceptible to peanut collar rot. However, only one cultivar exhibited weakly moderate resistance among the cultivars.4. Nine fungicide agents and six herbicides were tested to determine the toxicity effects on D. gossypina in the laboratory. The results showed that common fungicides remarkably inhibited the mycelial growth of D. gossypina. The studies of six herbicides on D. gossypina in vitro showed that toxicity of six herbicides to D. gossypina was different. Toxicity of haloxyfop-R-methyl is best and the worst is fluazifop-p-butyl,with EC50 are 33.2529μg·ml-1 and 971.5540μg·ml-1 respectively.5. Investigation and study on peanut collar rot in Shandong Province carrying out, the result showed that the disease has a high incidence in the main producing areas of peanut in seedling, mainly harms the basal stems and its branches, which has a closely relation with soil, climate and way of cultivation. There are usually two peak disease period and the first one usually appears in mid-June in the province's main producing areas. After mid and late August, with the plant senescing, disease index increases slowly and enters the second peak of disease. The field test showed that the control1 effects of tebuconazole + carbendazim , myclobutanil + carbendazim , thiophamate-merhyl and ovraclostrobin-metiram were 92.36%,76.74%,79.8% and 78.35% respectively.
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