| In recent years, clubroot of cruciferous plants caused by the soil-borne obligate parasite Plasmodiophora brassicae spread rapidly in many provinces. The disease is difficult to control because most commercial cultivars are highly susceptible. In this study, the host range of P. brassicae was investigated and resistance levels of the cruciferous plants were evaluated. The contents of glucosinolates in seeds of the different varieties of oilseed rape were measured aiming at investigating the role of endogenous glucosinolates in development of clubroot disease. The results were listed below:1. The host range of P. brassicae was studied by natural infection in open field and artificial inoculation in laboratory. Results indicated that no clubbed violet (Matthiola incand) was found both in the field experiemnt and in the laboratory experiment Therefore, violet is probably immune to P. brassicae or may be a non-host plant of P. brassicae. Similarly, wallflower (Cheiranthus cheiri), herbsophia (Descurainia sophia), Cress (Lepidium virginicum) were found to be the non-host plants of P. brassicae. For the investigated cruciferous weeds, pickpurse(Capsella bursapastoris) was found to be infected by P. brassicae in Sichuan, but not in Hubei, Guizhou and Yunnan. However, clubbed pickpurse plants were observed in the artificial infection experiment and P. brassicae was positively detected in the diseased roots by PCR.2. In the susceptible plant species in Brassicaceae, differences in resistance levels among cultivars and varieties were observed. About300varieties were planted in Changyang County and Zhijiang County, aiming at investigating the difference of resistance in2009and2010. There were100cultivars of Brassica napus,100varieties of B. campestris,100varieties of B. juncea,13other oilseed rape varieties and31varieties belonging to other cruciferous species. Results indicated that the disease incidence in B. napus, B. campestris and B. juncea ranged from10%to60%. The disease incidence in other rapeseed types ranged from8%to30%. M. incana, C. cheiri, D. sophia and L. virginicum showed no disease signs. The disease incidence in Orychophragmus violaceus was28%. 3. The content of glucosinolates in seed of cruciferous was tested using the HPLC method. The content of indole glucosinolates in the non-host or resistant varieties (0-5μmol/g meal) was significantly lower than that in the susceptible varieties (3-10μmol/g meal). According to the components and the contents of glucosinolates, the resistant cultivars (no disease signs) and susceptible cultivars were divided into two types, respectively. In resistant varieties, gluconapin is the main glucosinolate (GSL) in L. maritime. Sinigrin was the main GSL compound in M. incana and Iberis amrara. In the susceptible cultivars in Raphanus plants, Chinese cabbages and Capsella bursapastoris, Sinapis alba, Eruca sativa, and Brassica alboglabra, the main glucosinolates such as, the main GSL compound was sinigrin4. The effects of pure GSLs on germination of resting spores of P. brassicae were studied. Results showed that glucobrassicin, progoitrin,4-methoxyglucobrassicin and glucotropaeolin could promote germination of resting spores of P. brassicae at the early stage. Germination of resting spores was promoted by Pi-progoitrin and the promoting effect was enhanced with time. Germination of spores in the presence4-hydroxyglucobrassicin was not significant differen from with the control treatment at the early stage. However, germination was enhanced obviously from the fifth day. In a word, we concluded that all the GSLs tested in this study could promote the germination of resting spores of P. beassicae. Therefore the GSLs may play an important role in infection of P. brassicae. |
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