Study On The Antagonistic Mechanism Of Chaetomium Globosum To Plasmodiaphora Brassicae

Clubroot of canola, caused by the obligate parasite protist pathogen Plasmodiophora brassicae, is a serious soilborne disease worldwide. The disease occurs through the growing period of canola, which make root rot and even the whole plants die resulting significant economic losses, currently, there is no effective agricultural control and chemical control could be used to control this pathogen. The project intended to study the antagonistic mechanism of C. globosum against clubroot. The paper studied the dynamic colonizing, induced defense enzymes, control efficiency, isolation and identification of the active substance and the infection process. The main results are as follows:1、The colonizing dynamics of C. globosum on canola roots. After irrigating spore suspension of C. globosum, the number of C. globosum in canola roots was determined at different time. Its quantity in canola roots presented "first increased and then decline "trend. On the nineteen day, the quantity of C.globosum in the roots reached its peak9.9x102cfu/g.The results showed that C. globosum can colony in the canola roots with strong competitiveness, which palyed an important role in the biocontrol of clubroot.2、By measuring defense enzymes changes in canola leaves.The result showed that: The spore suspension of C. globosum were inoculated by irrigation root method. The activities of PAL, POD, PPO were higher than inoculated with the sterile water control. The activities of PAL and POD reached its peak at the five day after inoculation, with the peak values of2.2-fold (PAL) and1.4-fold (POD) higher than in the control plants, respectively. Activity of PPO was fluctuating, but its activity is still higher than the control. It suggested that induced systemic resistance was an antagonistic mechanisms of the C. globosum against canola clubroot.3、In greenhouse, the biocontrol experiment of C. globosum against P. brassicae showed that:The spore suspension of C. globosum was inoculated by irrigation root method, the disease incidence and disease index were significantly lower than inoculated with the sterile water control. The disease incidence decreased from76.64%to20%, the disease index decreased from48.6to11.11. Its control efficiency was76.88.4、Isolation and identification of antifungal compounds from C. globosum. The broth of C. globosum were studied by polarity gradient extraction, thin layer chromatography(TLC) and HPLC. The purified and isolated active substance can suppress the resting spores’ germination of P. brassicae The active substances had better thermal stablility, so it can not be protein macromolecules. The active substances including two compounds were identified as C16sphingosine and phytosphingosine via LC-MS. The MIC value for the two compounds against the germination of P. brassicae resting spores was less than0.1μg/ml.5、The process infection of P. brassicae in canola roots showed that:6days after inoculation, root hairs infection were first found; nine days after inoculation, differentiated zoosporangia were first found in the infected root hair cells; the cells of root cortex infection were first observed after fifteen days. Root hair infection appeared microscopic symptoms and root cortex infection appeared galled symptoms.These results indicated that C.globosum could induce defensive activity of calola and the sphingosine of C. globosum could inhibit the germination of P. brassicae resting spores. We initially confirmed that the antagonistic mechanism of C. globosum to P. brassicae were induced systemic resistance (ISR) and secondary metabolites.