Study On The Control Of Rotten Skin Disease And Growth-promoting Ability By Bacillus In Han Fu Apple Tree

Bacillus is widely distributed in nature and is one of the commonly used bacteria in biological control.It can control pathogenic bacteria by secreting antagonistic factors,secondary metabolites and inducing plants to acquire resistance.Meanwhile,it can improve soil and promote plant growth.Hanfu apple was studied by Shenyang Agricultural University.The rotten skin disease not only affects the development of fruit,but also endangers the health of the tree.At present,the prevention and control strategy of the rotten skin disease of Hanfu apple tree at the stage of chemical control,and it is urgent to develop a green and efficient biological control method.In this experiment,the biological control of apple tree rot was studied by using Bacillus.A total of 123 strains of Bacillus were isolated from 10 root soil samples of different plants in Xinyuan County,Xinjiang,and 8 species of Bacillus were identified by microscopic observation,molecular identification,physiological and biochemical identification.They are B.sonorensis,B.subtilis,B.amyloliquefaciens and B.licheniformis,B.simplex,B.aryabhattai,B.zanthoxyli,B.subtilis subsp.stercoris.B.licheniformis and B.subtilis were predominant,with 42 and 31 strains,respectively,while Bacillus aryabhattai,Bacillus amyloliquefaciens and Bacillus simplex were less,with 4,3 and 2 strains,respectively.Three primary biocontrol strains were screened out by measuring the physiological,biochemical and bacteriostatic abilities of Bacillus.They were Bacillus subtilis,Bacillus amyloliquefaciens and Bacillus licheniformis,respectively.At the same time,the optimal ratio of raw materials for Bacillus fermentation liquid was studied.Brown sugar:bean cake powder:beef paste:yeast extract=2:1:1:1,and the fermentation concentration was up to 1.01×10¹⁰CFU/m L.Three primary biocontrol bacillus strains were applied to the diseased apple tree branches to explore the control effect of Bacillus on apple tree mollusca.The results showed that the three primary biocontrol strains all had control effects,but the action modes were different.Compared with the control,Bli279 increased POD activity（1329.27U/g?min）after12 days of treatment with different Bacillus.Bam190 can increase PPO activity（133.4U/g?min）and decrease malondialdehyde（MDA）content（17.94μmol/L）.In addition,the expression level of PR1 gene was upregulated by 4.70 and 3.64 times compared with the control after 3 days of mixed treatment and Bli279 treatment,respectively.After Bam190 and Bsu181 were treated for 1 day,the expression of PR4 was up-regulated by 3.21 and 2.48 times compared with the control,respectively.In conclusion,strain Bli279 and strain Bam190 can reduce plant peroxidation and resist the damage of pathogens by increasing the activities of peroxidase（POD）and polyphenol oxidase（PPO）.Strain Bam190 can also reduce the content of malondialdehyde（MDA）in plants,reduce the degree of membrane lipid peroxidation and improve the resistance of plants.The expression levels of PR4,PR1 and PR4 were also increased in Bli279 and Bsu181,respectively.Three-year-old apple trees were irrigated with Bacillus fermentation broth to explore the growth promoting effect of Bacillus on apple trees.The results showed that after the Bacillus fermentation solution was used to irrigate the root of apple,the growth of the tree body was promoted in the aboveground part,the amount of leaf hanging on the side branches was increased,the leaves were full and dark green,and the stomata of the leaves was opened,and the absorption and utilization of water and inorganic salts were enhanced.Finally,the overall tree strength of Hanfu apple was improved.The underground part promoted the growth of lateral roots,improved soil PH,and enriched the number of probiotics in soil.In conclusion,three Bacillus strains with biocontrol function were screened out in this experiment,which can effectively promote the growth of Hanfu apple and have good control effect on apple tree mollusca.