Identification And Study On Biological Characteristics Of The Pathogen Of Fusarium Causing Tobacco Root-rot In Shandong Province

According to the harmful biological investigation of national tobacco from2010to2012, the rootrot of tobacco has become the one of the most serious diseases in the tobacco-planting areas. Thetobacco-planting areas in Shandong Province as research target, the thesis discussed the distribution ofthis disease, the identification of this pathogen and biological characteristics. All work hopes to providetheoretical basis for prevention and treatment of the disease. The main results read as follows:（1）Acquisition of typical root rot of tobacco samples from seven of the tobacco-planting areasin Shandong Province, a total of38strains of the pure culture were isolated. After validation of Koch’spostulation, we identified12strains of pathogenic fungus.（2）The result of morphological and molecular biological techniques of identification is that the12strains belong to three kinds, Fusarium solani, Fusarium oxysporum, and Fusariumchlamydosporium. Among them, F. solani can be isolated with highest frequency, accounting for58.3percent, while the second one is F.oxysporum, accounting for33.3percent. Both of them are mainpathogens.（3）F.oxysporum and F. solani have the same optimal growth conditions. In the condition of30℃, pH6~8, on the oatmeal agar, they would grow best. While the best conditons for Fusariumchlamydosporium are at20℃, pH8, on the Richard medium. The three kinds of Fusarium demand fornitrogen equal. In the medium with potassium nitrate as nitrogen source, pathogens grow significantlywith the most amount of spore production. On the contrary, the Fusarium grow slowly with no sporeproduction. F.oxysporum and F. solani grow significantly with vast sporulation quantity in the mediumwith sucrose as carbon source, while F. chlamydosporium grow in the medium with fructose as carbonsource.（4）The toxins of F.oxysporum and F. solani in liquid culture were extracted by ethyl acetate.The activity of toxins was identified by inhibition of seed radicle.The toxin of F.oxysporum and F.solani were both determined as the non-host-specific toxin (NHST). The toxin could be harmful toseeding root of tobacco. The symptoms of the toxin inducing lesion on tobacco root were similiar to thesymptoms caused by Fusarium inoculation. After the radicle of tobacco immersed in50%toxin, theenzyme activity of PPO, POD were measured. Within a certain period of time, the both enzyme activityextended gradually increased over time, but went down at last. After the radicle of tobacco immersed in50%toxin, measure permeability of cytomembrane of the root and lamina. Within a certain period oftime, the both extended gradually increased over time, but stabilized at last.