Plant pathogenic fungi produce mycotoxins which may lead host plants to produce disease symptoms and may have a significant positive role in the course of disease development.The putative Phytophthora infestans toxins were prepared by culturing in liquid medium(60 g rye and 10% tomato juice L-1) for 1 mon at 17℃,filtering through four layers of cheesecloth and being precipitated by ammonium sulfate.The resulted putative toxin solutions were used to study the effects on 3 potato varieties(both leaf and tuber tissues).The results show that potato leaves and tubers exhibit symptoms similar to the late blight resulted from P.infestans infection.Potato varieties reacting differentially to both the toxin dilutions and toxins produced by different P.infestans isolates suggested the presence of toxin-mediated specificities between potato and P.infestans.Potato leaf and tuber tissues have different and contrary reactions to the toxin.Toxin-mediated specificities are likely present between potato and P.infestans. Plant pathogenic fungi produce mycotoxins which may lead host plants to produce disease symptoms and may have a significant positive role in the course of disease development. The putative Phytophthora infestans toxins were prepared by culturing in liquid medium (60 g rye and 10% tomato juice L -1) for 1 mon at 17 ° C, filtering through four layers of cheesecloth and being precipitated by ammonium sulfate. The resulting putative toxin solutions were used to study the effects on 3 potato varieties (both leaf and tuber tissues). The results show that potato leaves and tubers exhibit factors similar to the late blight resulted from P. infestans infection. Photolith to both the toxin dilutions and toxins produced by different P. infestans isolates suggested the presence of toxin-mediated specificities between potato and P. infestans . Potato leaf and tuber tissues have different and contrary reactions to the toxin. Toxin-mediated specificities are likely present between pot ato and P.infestans.