| Garlic tip blight is considered as a disease on Garlic, the disease become serious on greenhouse in recent years. This study is carried on the pathogen biological characteristics, toxin activity. The aim of experimentation was to research the optimum conditions of the growth of pathogen mecylium, the conidia production and toxin production by the Stemphylium. Then we could use phytotoxin to select cell variant mutant lines of resistant Garlic tip blight which had steady transmissibility.1. Collection and pathogenic identification of the pathogenThe morphologic and pathogenic identification of the pathogen shows that this pathogen on the diseased leaves, collected from Zhouzhi town and Yangling city of Shannxi province, is belong to Stemphylium Wallroth, and the disease symptom and pathogen characteristics are described.2. Study on the biological characteristics of Stemphylium Wallroth.The conditions of the growth of pathogen mecylium and the conidia production including medium, culture temperature, lightening, pH value were systematically studied to measure a size of pathogen spot.The results show, in pH 7 PDA, PCA, CSA and PSA medium,the growth of pathogen mecylium is diferent on four kinds of media. PSA is the most suitable media, the PDA takes the second place. In the test of culture temperature, pH 7 PSA medium of Stemphylium are cultivated at 15,18, 20, 22, 24, 26, 28 ,30, 35 and 40℃separately, the temperature for mecylium growth is from18℃to 35℃and 28℃is the optimum.The temperature for conidia production is from18℃to 35℃and 28℃is the optimum.The range of the conidia production temperature is from 18℃to 35℃with optimum 26℃. In the test of lightening, pH 7 PSA medium of Stemphylium are cultivated under 24 D, 24 L, and 12 L/12 D separately, the light has little effect on the mecylium growth. The light condition is relatively suitable to the conidia production. In the test of pH value, pH 4, 5, 6, 7, 8, 9,10,11 and 12 PSA medium of Stemphylium are cultivated separately ,the pathogen can grow under pH from 5 to 12 with optimum pH 8. The range of the conidia production pH is from 7 to 9 with optimum 8. 3. Study on the toxin and toxicity of Stemphylium Wallroth.The conditions of toxin production by the Stemphylium, including medium, culture temperature, lightening, vibration, pH value and culture duration were systematically studied by Welsh onion seed germination test of the toxin toxicity. The results showed that in pH 7 PS, I-Fries, I-Richard and Czapek-Dox liquid medium, the crude toxin produced from Czapek-Dox liquid medium has strongest inhibition for Welsh onion seed germination in all medium and on the 20th day of culture, The welsh onion seed germination percentage is only 10.5%. In the test of culture temperature, pH 7 Czapek-Dox liquid medium of Stemphylium are cultivated at 18, 20, 22, 24, 26, 28 and 30℃separately, the ability of crude toxin produced at 24℃is strongest and on the 20th day of culture, The welsh onion seed germination percentage is only 10.0%. In the test of lightening and vibration, pH 7 Czapek-Dox liquid medium of Stemphylium are cultivated under 24D-S, 24L-S, 24D-V, 24L-V, 12L/12D-V and 12L/12D-S separately, the crude toxin produced under 24D-V has strongest inhibition for Welsh onion seed germination and on the 20th day of culture, The welsh onion seed germination percentage is only 10.5%.In the test of pH value, pH 4, 5, 6, 7, 8, 9 and 10 Czapek-Dox liquid medium of Stemphylium are cultivated under 24D-V during 20 day separately, the crude toxin produced in pH 6 and 7 have strongest inhibition for Welsh onion seed germination and on the 20th day of culture, The welsh onion seed germination percentage are 13.0% and 10.5%. The results also showed that the optimum conditions were Czapek-Dox liquid medium in pH 6～7, culture temperature 24℃, with successive dark and vibration during culture. The production of crude toxin reached the highest level on the 20th day of culture.
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