Evaluation And Control Mechanism For Suppression Of Biological Soil Disinfection To Club Root Of Chinese Cabbage

Clubroot is a serious soilborne disease of cruciferous crops caused by Plasmodiophora brassicae Woronin worldwide and a difficult problem because its pathogen's resting spores can live in soil for at least 10 years. To control club root of Chinese cabbage and reduce environment pollution by chemicals application, the mechanisms of disease control and yield increase were studied by biological soil disinfection with fresh Brassica oleracea var. caulorapa de Candolle, Artemisia apiacea and Eupatorium adenophorum in the laboratory, the greenhouse and the field.In PSA medium, Brassica plants had better biofumigation effect on fungi than non-Brassica plants with dosage effect, among which B. oleracea var. caulorapa showed best suppression. Ten gram of B. oleracea var. caulorapa ground powder perФ9 cm plate by adding the powder in the cover and updown culture suppressed 26.2%-100%of mycelial growth for 30 fungi belonging to 11 species. Ceratocystis fimbriata, Phytophthora parasitica and Sclerotinia sclerotiorum were most sensitive to the plant and Pythium aphanidermatum was most unsensitive. E. adenophorum and A. apiacea suppressed 20 and 17 isolates, respectively.B. oleracea var. caulorapa, E. adenophorum and A. apiacea had different volatile compounds and few common ones based on high performance liquid chromatography (HPLC) and gas chromatograph-mass spectrometer (GC-MS) analyses. A. apiacea and E. adenophorum had more volatile compounds than oleracea var. caulorapa. Only were volatile Allyl-ITCs found in B. oleracea var. caulorapa, A. apiacea and E. adenophorum contained mainly aromatic compounds.E. adenophorum and A. Apiacea yielded and reduced club root more than B. oleracea var. caulorapa in the greenhouse experiments in two years. Biological soil disinfection combined with plastic nutrient sac seedling when transplanted in 25 days could control club root and increase yield effectively.Bacillus subtilis XF1 and Pseudomonas sp. XF2 from rhizospheric soil of Chinese cabbage could control club root in the greenhouse very efficiently. No symptom appeared in 60 days and 30 days after XF1 and XF2 application with 109CFU/mL suspension, respectively. Both strains controlled disease with 89.2% and 46.0% and increased Chinease cabbage 219.5% and 139.3%, respectively, in harvest period.Disease index declined gradually in 3 continual field trials by biological soil disinfection. Control effects were 41.9%, 41.8%, 31.1%, 28.6%, 28.5%, 27.6% and 19.8%; yield increased 8.3%, 44.9%, 30.1%, 29.2%, 24.2%, 16.1% and 9.6% averagely, respectively, by liming, A. apiacea plus lime, E. adenophorum, E. adenophorum plus lime, A. apiacea, B. oleracea var. caulorapa plus lime and B. oleracea var.caulorapa. Based on the investigation on nutrient elements in the soil, liming reduced efficient nitrogen, boron, sulphur, copper, zinc and manganese, increased efficient phosphorus, organic matter, pH value and exchangeable calcium, and did not change efficient potassium status. For yield increase, all plant materials were better than liming, but the mix of liming and plants were better than single plant. B. oleracea var. caulorapa was the worst in disease control and yield increase compared with the other treatments even though it showed the best biofumigation effect in PSA medium.The relatedness between control effect and 13 factors were in the oder: Fe> Mn > Ca > B >organic matter > K > Cu > Zn > Ec value> pH > S > P > N in effecience. Efficient Fe reduced by 47.7% and showed most significantly positive correlation with efficient B, Cu, and Mn and significantly with Ca, but nagetive with pH value. The relateness between yield increase and the 13 factors followed the order: K> pH value >organic matter > Ca >B > Fe > Mn > Zn> Cu > N > Ec value > P > S in efficient status for all factors. Efficient K increased yield to 154.6% when it was mixed with lime. It correlated positively to organic matter most significantly, to efficient P and Zn. By plating method and denatured griendent gel electrophorosis (DGGE), culturable microbes in the soils increased 80.9%, 39.5%, -18.4%, 82.6%, 81.6%, 20.8% and 6.8% by the treatments with B. oleracea var. caulorapa, B. oleracea var. caulorapa plus lime, lime, A. apiacea, A. apiacea plus lime, E. adenophorum, and E. adenophorum plus lime in the 3 continual field trials compared with the treatment without any materials (CK), indicating that plants increased microbe amounts and only liming reduced the amounts. Species number of microbes showed some difference among the soils based on the band data of DGGE. Microbial community dynamics in the soils was analyzed in the third season through ECO Biolog microplates. Community level physiological profiling (CLPP) showed that average well colour developments (AWCD) of A. apiacea and A. apiacea plus lime were the highest (0.952), and AWCD of B+L was the lowest (0.662). From the community diversity index, Simpson index of CK was significantly higher than the other treatments; Shannon-Wiener index (H')of the treatments with plant materials were higher than with liming; Shannon-Wiener (J') of treatments with liming were lower than others. According to Factor analysis, the carbon-source utilization of amino acids and carbohydrates was important to access metallization of soil.It was reported that myrosinase affected biofumigation. Therefore, the degenerate primer pairs, MyrBs: 5-ACAGRTTCTCCWTHGCGTGG-3 and MyrBa: 5-ATBTWC- CHYTTGTTAGCGGC-3 were designed to investigate the distributions and sequences of myrosinase gene among 18 plants, 2 fungi (Trichoderma harzianum and Colletotrichum gloeosporioides) and 2 bacteria (Bacillus subtilis and Pseudomonas sp.). The sequences from 11 Cruciferae, 2 Compositae(Lactuca sativa and E.adenophorum) and 1 Solanaceae(Nicotiana tabacum), showed highly homologic to known myrosinase genes, but other 8 lowly based on blastn results at the internet database. The sequences from 11 Cruciferae conserved relatively,The possible mechnisms of biological soil disinfection to control club root of Chinese cabbage are: 1. the plants could release votalie compounds to inactivate microorganisms in soil; 2. the plant residues could inprove growth conditions, increase cabbage resistance, reduce disease severity and increase yield by affecting soil physical and chemical natures and population of soil microorganisms.