Superoxidation of membrane lipid in corn leaf cells has been studied by researching the relationship between membrane permeability,the content of MDA,and the activity of POD and SOD under HT\|toxin stress.The experimental results showed that the content of MDA ascended,the POD activity was stimulated and SOD activity was inhibited in compatible combination,but POD activity was inhibited in incompatible combination.HT\|toxin strongly destroyed the permeability of cell membrane of corn,and there were positive correlation between toxin effect and toxin concentration and time exposure to toxin.It was conclusion that there may be toxin\|binding site in both resistant and susceptible cell membrane,and the difference in sensitivity of resistant and susceptible cells to toxin may result from their active oxygen metabolism.

Effect of 8 fungal fermented filtrates on mycelial growth, encystment and germination of zoospores, appressorium formation, and penetration hyphae formation of Phytophthora infestans was investigated. Of which, the fermented filtrates from Rhizoctonia solani and Colletotrichum gloeosporioides showed the strongest inhibition against P. infestans. The results indicated that they are potential for controlling the diseases caused by P. infestans.

Ht-toxin was extracted by singular or mixed organic solvents after solid and liquid culturing Helminthosporium turcicum in vitro, and pathogenic activity and toxicity of these extracts were assayed using root growth inhibition, isolated root cap cell death and isolated leaf soaking bioassays. Several best singular and mixed organic solvents have been screened for extracting Ht-toxin in vitro and this may lay foundation for its purification and structure analysis.