Abstract: Observations were made on the regular patterns of toxin production of Alternasia solani (tomato early blight disease) on PD media.Results have shown that the pathogenicity of toxin increased quickly as culture proceeds. The pathogenicity reached the maximum value after 40 days of culture, and then got lower and lower as the culture went on. The regular pattern of the changes on the PD medium was a quadratic curve which may be shown in the following equation : y= -9.06245+2.9656x-0.0306x2. The test also indicated that transparency of the filtrate declined as the time of culture went on, and got the lowest at the 35th day, and then the transparency increased a little with time extension. This pattern of changes may be expressed by the following quadratic curve: y = 89.508- 3.743x + 0.048lx2. The soluble substances in the filtrate decreased with the increase of culture time. In general, the decrease was faster during the first 30 days, after that the decline speed turned to slow. The regular pattern remained tobe a quadratic curve (y = 3.397- 0.0827x + 0.00046x2). The soluble substances disappeared until the 60th day. The pH of the filtrate increased with the culture time. And it increased faster in the first 40 days, then pH increase got to slow. The pattern of speed increase could be expressed by the equation. y= 5.44 + 0.0392x-0.0002x2. The results have shown that one liquid medium is similar to the other. Therefore, it is considered that the optimum period of toxin production for A, solani is around 40 days as long as PD is used in a still condition at 25℃.Then toxin production decreases as nutrients are depleted. And it is also considered that the transparency rate of the filtrate may be regarded as a reflection of the toxin lovel. The content of toxin is the highest when transparency is the lowest.

Key words: Alternaria solani, Prepation of toxin