| Bacillus subtilis is an important biocontrol bacteria.Its biocontrol mechanism is mainly competition,antagonism,bacteriolysis induced resistance and synergy.It is safe,not easy to produce drug resistance,and has significant control effect on many crop diseases.It has become a hot spot of modern agricultural medicine research.Wheat(Triticum aestivum L.)is one of the main crops in China.Various diseases often occur in agricultural production.Powdery mildew is one of the main diseases.Wheat powdery mildew is a kind of fungal disease caused by wheat specific form of powdery mildew(BGT).It has a large area and a heavy degree,and has a very serious impact on the yield and quality of wheat.In this experiment,wheat was used as plant material and powdery mildew as pathogen to study the biocontrol mechanism of Bacillus subtilis microcapsule on wheat powdery mildew.1.The taxonomic status of TP-08 was identified.The results of morphological observation showed that the colony of the strain was small,micro long or flat,the surface was rough and opaque,micro yellow or white;The results of physiological and biochemical indexes showed that the strain was aerobic,and could produce catalase,α-amylase and neutral protease,and had a strong nucleotide degrading enzyme system,the V.P.test was positive;The results of molecular identification showed that the similarity of the TP-08 and Bacillus subtilis strain was as high as 99%.TP-08 was identified as Bacillus subtilis.2.The effect of Bacillus subtilis on wheat growth and the control effect of powdery mildew were studied.It showed that Bacillus subtilis could improve the germination rate of wheat,promote the growth of root system,stem and leaf.Among all,the effect of 4×10~5CFU/m L was the best:germination rate of seed increased by 1.56 times,and the plant height increased by 38.48%;For the control of powdery mildew,the effect of 4×10~5CFU/m L of Bacillus subtilis microcapsule solution was the best:71.75%for wheat in vitro leaf segment and 77.90%for wheat in pot。3.The effect of Bacillus subtilis on wheat defense related enzymes and the infection process of powdery mildew was determined.The results showed that the relative activities of CAT,POD and SOD were increased to 5.24,8.79 and 7.54 in the 4×10~5CFU/m L group,which were 3.80,4.05 and 2.65 times higher than those in the control group,respectively.During the infection process,the high concentration of Bacillus subtilis showed significant inhibition on powdery mildew:the growth of germ tube slowed down,the germination rate of spore decreased,the rate of tube deformity increased and the development of spores was hindered.The effect of 4×10~5CFU/m L of Bacillus subtilis microcapsule solution was the best:22.23%of spore germination rate,decreased by 3.88 times than control,69.33%of germ tube deformity rate,5.07 times higher than control,and the germ tube length was71.35μm,1.51 times longer than control.After treatment with Bacillus subtilis,the accumulation rate of ROS and the rate of cell death area were higher than those of the control,the highest were 1.78 and 1.37 times than control.4.The effect of Bacillus subtilis on wheat transcriptome was analyzed by RNA-seq.A total of 5924 differential genes were obtained,2435 of which were significantly up-regulated and 3489 significantly down-regulated.After GO database enrichment,it was found that most of them are enriched in the biological processes such as amino acid biosynthesis and metabolism,active oxygen metabolism(BP);Cell components including apoplast,chloroplast,cell wall,cell membrane(CC);Molecular functions mainly concentrate on vitamin binding,oxidoreductase activity(MF).The results of KEGG pathway enrichment analysis showed that the differentially expressed genes were mainly enriched in amino acid biosynthesis and metabolism(including phenylalanine),carbon metabolism,pentose phosphate pathway,glutathione metabolism,phenylpropane biosynthesis,polysaccharide metabolism,photosynthesis,etc.Among them,plant hormone signal transduction gene NPR1 was significantly up-regulated,indicating that Bacillus subtilis was able to induce systemic resistance(SAR)of wheat through SA-dependent pathway to defend powdery mildew. |
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