| Mongolian snakegourd (Trichosanthes kirilowii) is an important traditional Chinese medicine. Trichosanthin (TCS) can be extracted from the root of Mongolian snakegourd, which can inhibit the propagation of HIV. Along with the enlargement of culture area of Mongolian snakegourd, its anthracnose caused by Colletotrichum sp. has been a serious problem and it can bring numerous yield losses. However, so far its pathogen is unknown for us. In the dissertation, eight isolates of Colletotrichum were obtained from diseased fruit and foliage of Mongolian snakegourd, single-spore-cultured, grown on potato dextrose agar (PDA) from Qian'shan county, Anhui province, China P.R. Then, Polyacrylamicide gel electrophoretic analysis of isozymes of 8 isolates of Colletotrichum from Trichosanthes Kirilowii and 4 isolates of four other apple,watermelon,corn and dogwood were studied as an accessorial method for the taxonomy of anthracnose pathogens. The effects of diverse environmental factors and nutriments on the growth of Mongolian snakegourd anthracnose pathogens, the variety and activity of extracellular enzyme secreted by Mongolian snakegourd anthracnose pathogens were studied. Also the effects of the fungicides and biocontrol stain B-24 to control this disease were studied. The experimental results were summarized as follows:1. The Identification of Mongolian snakegourd Anthracnose Pathogen According to the experimental results of cultural and morphological characteristics, pathogencity and host range test, meanwhile, consulted the classification criteria of Colletotrichum edited by Sutton (1980), the pathogen of Mongolian snakegourd anthracnose was identified as Colletotrichum orbiculare (Berk. &Mont.) Arx primarily. The cultural characteristics were some differences among eight isolates from diverse locations on PDA medium.The results of pathogenicity test to Mongolian snakegourd showed some difference among eight isolates. Isolate S5 had the strongest pathogenicity to Mongolian snakegourd, while isolate S9 showed the weakest pathogenictiy among eight isolates. The pathogenicity of other six isolates showed no apparent differences by means of Duncan's test. Mongolian snakegourd didn't be infected by unwounded inoculation.The host range of C.orbiculare was investigated by inoculating several dozens of plants with the methods of conidial suspension wounded and unwounded inoculation. The results indicated that Mongolian snakegourd anthracnose pathogen could infect 13 kinds of plants from 10 families by means of wounded inoculation. These plants included Camptotheca acuminata, Magnolia grandiflora, Humulus scandens, Citrullus lanatus, Platanus hispanica, Broussonetia popyrifera, Euonymus japonica, Ipomoea batatas, Cucurbita pepo, Luffa cylindrical, Malus pumila, Cucumis sativa, Lycopericon esculentum,etc.2. Study on the physiological and ecological characteristics2.1 The Overwinter Survival Ability of Mongolian snakegourd Anthracnose PathogenMongolian snakegourd anthracnose pathogen could overwinter safely at the range from 0℃ to 15℃. Due to the low temperature, C. orbiculare could not be isolated from diseased organism. When the water content in soil was at the range from 0% to 25%, C.orbiculare could overwinter safely indoor, too. C.orbiculare was isolated from the outer and inner of the overwinter seeds. So, the diseased fruits, diseased leaves and diseased seeds were proved to be the major initial effective sources of anthracnose. C.orbiculare on Mongolian snakegourd was not strict with the overwinter conditions.2.2 The Effect of Diverse Environmental Factors on the Growth of Colletotrichum orbiculareThe results showed as follows: the growth optimum temperature ranged from 21℃ to 30℃.The mycelia grew best at 28℃. Low temperature such as 0℃,inhibited hyphal growth and conidia germination only, but was not the deadly line. C.orbiculare could not survive at high temperature such as 40℃. Conidia couldn't germinate under 10℃ or above 40℃. The percentage of conidia germination of diverse isol... |
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