| Silene conoidea L. is a common annual weed worldwide. It can be found mainly in the field of wheat and causes crop substantial yield reduction mainly through competition. Phytophthora.spp is considered to have potential for the biological control of weeds. An indigenous strain of Phytophthora.nicotianae (WP-1) was isolated from Silene conoidea in Tai'an, Shandong, P.R.China, in2003. The objection of this study were, 1) to evaluate safety of the pathogen as a mycoherbicide; 2) to assess the effect of inoculum's concentration, host-plant growth stage, dew period, oil emulsions and chemical herbicide on the pathogenicity of Phytophthora.nicotianae (WP-1) against Silene conoidea; 3) to determine biological characteristic.1 The result of candidate's host range tested with 37 plant species showed that the pathogen was safety except for several plant species of Caryophyllance, Achyranthes and Cruciferae. Susceptive plants were killed by a postemergence damping-off. When formulated as liquid mycelial and given a 24h dew period, more than 50% mortality of Conical Silene, Flixweed Tansymustard and Redroot Amaranth was achieved with postemergence treatments.2 The pathogenicity of Phytophthora.nicotianae (WP-1) increased with increasing inoculum concentration and dew period. At the second to fourth leaf stage, S. conoidea.was most sensitive to the pathogen, in older plants (older than four-leaf stage) infection and mortality are lower. For the disease development the optimal temperature was 15-25℃.When formulated as granules in a fungus-infested barley preparation and given a 24h dew period, an inoculum concentration of 3.0g/m2 caused 79.37 % mortality of the second leaf stage plants. The higher levels of plant mortality were obtained with a high inoculum concentration (at least 3.0g/m2) in a rapeseed oilemulsion at the second to fourth leaf stage plants and given a long dew duration (at least 24 h).The virulence of different formulations and application methods was investigated. Liquid zoospore applications are more effective; Preemergence applications that are applied to the soil surface after planting proved to be most effective.3 Sequential applications of sublethal rates of Tribenuron-methyl and the plant pathogen Phytophthora.nicotianae were assessed for integrated control of Silene conoidea.. Phytophthora.nicotianae (WP-1) was prepared as a granular treatment of fungal-colonized barley grits. Sequential applications of sublethal rates of Tribenuron-methyl and the plant pathogen Phytophthora.nicotianae caused greater damage than either treatment alone. This synergistic interaction may reduce the rate of either component required for adequate levels of control, possibly decreasing the cost or volume of use of herbicides in traditional weed control strategies.4 For mycelium growth, the optimal temperatures range from 20℃ to 28 ℃; The optimal initial pH of culture media range from 4 to 9; the optimal culture condition was TA media in solid, CFB media in liquid, independent on the tissue juice of Silene conoidea L, with 24 hours light every day; Mycelium could grow in either dark or light, pH 4 ~9 ; Shaking culture 15 days. The result of bioassay showed that the crude of filtrate from the strain is toxic to Silene conoidea L. Although the filtrate doesn't inhibit the germination of seeds of Silene conoidea L., it could significantly restrain the growth of the root. For producing phytotoxin of this fungus, it was found that the optimal cultural conditions were temperature 25℃,pH about 4-5, dark and static, in Plich'S media for 15 days.
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