Studies On Isolation And Purification Of Mycotoxin Produced By Exserohilum Turcicum Race 2

Northern Leaf Blight of corn is one of major diseases in corn planting area. Its pathogen, Exserohilwn turcium, could produce a kind of host-selective toxin, which cause typical symptom on the leaves. The questions as follows had been made clear through the study on extracting, purifying and fraction analysis to the toxins produced by Exserohilum turcium race 2. (1) Exserohilum turcium could produce toxins after being cultured in the modified Fries nutrient solution, and the toxicity to corn of the filtrate after being cultured for 2ldays did not decrease after being freeze-dried and dropped the precipitate when methanol added. (2) The culture filtrate was extracted with ethyl acetate, chloroform and ethyl ether by step or respectively, then high performance liquid chromatography (HPLC) analysis was done to all the extracts. The results showed that the number of the peaks of each extract was similar, and it was speculated that the HI-toxin could be dissolved in the three organic solvents above. Using the two bioassays of isolated root cap cells and prodding the leaves in vitro, the experimental results showed that ethyl acetate was the best organic solvent to extract the HI-toxin. (3)The ethyl acetate extract (crude toxin) was scanned with the UV spectrophotometer and four absorption peaks (respectively at 206,21 5,227,257nm) were found. After compared with other peaks, the peak at 257nm had a wide absorption scope and the noise signal was slight. (4)HPLC analysis was done to the ethyl acetate extract by eluting with different ratio of methanol and acetonitrile. It was found that the composition and the ratio had a largely affect on the isolation effects of the HT-toxin. Under the best eluting condition, the HT-toxins could be isolated as 8 main fractions. (5)AlI the fractions isolated were prepared with the Ci preparative column and it was found that fraction 7 and 10 had obvious toxicity to corn through the bioassay. (6)The retain time of standard fraction I (5-hydroxymethyl-2-furancarboxaldehyde) was the shortest by HPLC under the same isolation condition when it was compared with the figure of the other fractions obtained in this thesis. The hypothesis was proposed that the molecule weights of the other fractions obtained in this research were larger than toxin I (7)All the fractions were scanned by Infrared spectrum and their absorption spectrum were compared. The results showed that the two toxic fraction (7 and 10) had the analogous spectrum, the shape of their peaks were coincident, only the wave numbers had slightly difference. The Infrared spectrum of the other non-toxic fractions has some difference with the toxic ones, but fraction 4 and 6 also belonged to the same kind.