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Several methods were evaluated in an attempt to develop a greenhouse screening procedure that would predict field resistance of brassica breeding lines to clubroot disease caused by Plasmodiophora brassicae. Several Brassica oleracea cultivars and breeding lines bred for resistance to Plasmodiophora brassicae and a susceptible Chinese cabbage cultivar were exposed to high levels of inoculum of both pathotypes PB 6, PB 7 at 12,15,20, 25 and 30°C. No infection occurred on any host at 12°C. Chinese cabbage was heavily diseased from 15 - 30°C. Bagder Shipper cabbage, a cauliflower deriving resistance from this variety, and Oregon CR-1 broccoli were resistant to pathotype PB 6 at 15 and 20°C and partially resistant at 25 and 30°C. They were resistant to pathotype PB 7 and 15°C and almost totally susceptible at 20, 25° and 30°C. Oregon cabbage line OR 123 was resistant to pathotype PB 6 at 15°C at almost completely susceptible at 20, 25 and 30°C. It was resistant to pathotype PB 7 at all temperatures. Temperature sensitivity of resistance can partially explain why breeding lines are resistant in field trials and susceptible in greenhouse tests.
Clubroot presents a serious threat to cultures of oilseed rape, especially if the share of this plant species in sowing structure is high. This is related to a long-lasting survival of pathogens resting spores in soil. The casual disease agent is Plasmodiophora brassicae Woronin - an obligatory, internal pathogen of Brassicae family which causes the formation of tumors on roots and hypocotyls. Plants with disease symptoms have a confined ability of nutrients' and water uptake and this may cause considerable losses in quantity and quality of potential yield. Monitoring performed in cultivation areas and the information obtained from farmers allowed to confirm a threat of disease occurrence in several voivodeships. At the same time there is a serious danger of the infection spread to other regions of oilseed rape crops. Confining plant infection by clubroot pathogen may be obtained mainly by applying a correct crop rotation, and also by providing resistant varieties for cultivation. In the performed greenhouse experiment, reaction to the infection caused by P. brassicae of chosen winter oilseed rape cultivars was studied. The degree of plant infection was assessed at the growth phase of green bud. It was stated that cv. Mendel revealed significantly the lowest degree of infection, as compared to the other studied cultivars. The other tested varieties were infested in a differentiated degree, however these differences were mostly not confirmed statistically. The infection level was mainly dependent on places of soil derivation.
Several factors, including growth medium, inoculum density, and inoculum storage affected the reaction of resistant and susceptible Brassicas to Plasmodiophora brassicae in the greenhouse. A high level of disease was achieved using Peat-litte mix R and a commercial greenhouse mix. There was little difference in disease incidence when spore suspensions were pipeted into planting holes or when seedlings were dipped into spore suspensions. Seedlings transplanted from sand or Petri dishes gave higher levels of disease than direct seeding. Two-year frozen storage of clubs reduced the inoculum potential to a level unable to define resistance. Inoculum levels of 10³⁻⁷ spores per ml from fresh clubs, or 10⁵⁻⁷ spores per ml from clubs frozen for 2 or 4 years, produced 90% club incidence of susceptible cauliflower and Chinese cabbage. A concentration of only 10⁶⁻⁸ spores per ml from fresh clubs was required for maximum disease expression in a cauliflower line partially resistant to clubroot.
On soils heavy contaminated with Plasmodiophora brassicae growing any susceptible crop of brassicae is impossible even using fumigation method involving the use of calcium cyanamide or dazomet. The satisfactory results suggested that resistant crucifers might effectively reduce numbers of resting spores of P. brassicae in soils. The total lack of disease symptoms was achieved when used disinfection with calcium cyanamide (Perlka 1,000 kg/ha) and sowing resistant winter oilseed cultivar Mendel F1 and Alister F1.
Clubroot disease is one of the most serious diseases of oilseed rape and other Brassicaceae species. The disease causual agent is an obligatory parasite – Plasmodiophora brassicae. Typical symptoms of the infection are specific round tumors on roots. Several pathotypes of P. brassicae are known. It is possible to identify the pathotypes using a root hair test or by PCR. The aim of the study was to check the possibility of using PCR to identify oilseed rape infection by P. brassicae and its P1 pathotype. Plant samples with clubroot sympthoms were colleted from Poland in 2008–2009. PCR primers specific to P. brassicae and pathotype P1 were used. Infection of 44 tested plants by P. brassicae and the presence of P1 pathotype in six samples was confirmed PCR reaction. The occurance of clubroot disease was also recorded on Shepherd’s Purse, which may be considered as a potential inoculum source of this pathogen.
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