Preliminary Study On The Pathogenic Substance Produced By Pestalotiopsis Photiniae

Currently, strawberry root rot is one of the most serious and devastating diseases in strawberry gardens. Most of the strawberry gardens have been destroyed in the whole world. The areas of strawberry plants have been expanding rapidly in China since the 1980s. But, each year the production of strawberry have suffered enormously economic losses from the disease. In this study, it set predominant fungus of strawberry root rot——Pestalotiopsis photiniae (Thuem) Y. X. Chen for the object. The biochemical characteristics of pathogenic substances, especially for production conditions, capacity, and fundamental characteristics of toxins generated by P. photiniae, as well as the isolation and purification of toxins, were preliminary investigated for the first time. These researches may provide a theoretical basis for further understanding on the pathogenic mechanism of the toxin and on the pathogenic composition of the toxin. And then, the use of toxins for resistance screening of strawberry varieties and the biological control of strawberry root rot are expected to obtain.The kinds of pathogenic substances produced by P. photiniae causing strawberry root rot were confirmed initially. The proteins and toxins obtained form culture filtrate were measured with the method of needle puncturing leaves. The results showed that the toxins (0.355mg/mL) had evident pathogenic activity, but the proteins had not.The influence exerted by culture conditions on production of P. photiniae was detected with the method of leaf disks. The test result showed that the most suitable conditions for the toxin production were adjust pH value of culture medium at 6.2, culture temperature at 25℃, darkness and stillness culture for 5-7d. The most suitable conditions for the toxin production and their growth conditions are not totally consistent.The fundamental characteristics of crude toxins were investigated in this test. The results showed that pathogenic toxins was a low molecular weight substance (less than 10 kD). Its thermal stability was well. The pathogenic activity was significantly different from pH, and that was the hightest at pH 2.5. The higtest absorption peaks was 200 nm under UV light. The pathogenic substances produced by P. photiniae were preliminary isolated. The pathogenic activities of crude toxins extracted by three kinds of different polar organic solvents (petroleum ether, ethyl acetate and chloroform) were significantly different. The effect of extraction by ethyl acetate was the best. The recovery of crude toxins could be as high as 97.8 percent. So the preliminary isolation of the toxin by the middle-polar solvent ethyl acetate is effective.By the method of column chromatography and TLC, the crude toxins were further purified. Eight different groups of solvent elution system were determined according to polarity from weak to strong in silica gel column chromatography, and the component only from one system (petroleum ether: ethyl acetate=1:1) had the pathogenic activity. Then, nine components were obtained by TLC (developing agent system was ether: ethyl acetate= 1:5), in which both V (Rf=0.59) and VI (Rf=0.55) had pathogenic activity.