| China’s citrus planting area and production are among the world’s forefront,with an area of more than 40 million mu in 2021,output of 54 million tons,output value of 330billion yuan,becoming China’s export advantageous agricultural products.However,postharvest disease rot of citrus leads to huge economic losses,the rot rate is between 20%and 40%.Currently,the main control measures after harvesting citrus or chemical control is still the main,but the residues of pharmaceuticals,pathogen resistance and other issues make the use of chemical fungicides are restricted even banned.Biological sources of preservative preservation agent development is very active,but only the direct use of antagonistic bacteria,there is not strong prevention,inconvenience,narrow inhibition spectrum,short shelf life and other deficiencies.Therefore,this study attempted to develop a combination of antagonistic bacteria with certain products（such as tea saponin）.The main research results are as follows.（1）More than 10 pathogenic strains such as Penicillium italicum and Penicillium digitatum were isolated from Gannan navel oranges and Nanfeng mandarin fruit after harvest.Using the plate coating dilution method,morphological observation and molecular phylogenetic analysis,a new pathogen of the genus Diaporthe was identified and named as Diaporthe qicheng after the host.（2）The mycelial growth rate method was used to determine the inhibitory activity of Bacillus velezensis UB201712 and tea saponin against P.italicum and P.digitatum.The results showed that the EC50 of Bacillus velezensis UB201712 against P.italicum and P.digitatum were 198 cfu/ml and 858 cfu/ml respectively;the EC50 of tea saponin against P.italicum and P.digitatum were 1.40 mg/ml and 2.40 mg/ml respectively.The two were found to have the strongest inhibitory effect on the two pathogens in different ratios of Bacillus velezensis:tea saponin=9:1（v/v）,and the 9:1 combination was more effective than the single ingredient in the control of citrus green mold.（3）Through the screening and optimization of microbial compounding auxiliaries,the best formulation of Bacillus velezensis UB201712 wettable powder was obtained as follows:the main active ingredients are Bacillus velezensis and tea saponin,carrier diatomaceous earth（85-92%）,wetting agent Tween-80（2.4%）,dispersant sodium lignin sulfonate（3.6%）,stabilizer dipotassium hydrogen phosphate（2%）,protectant SDS（0.5-1.0%）,the powder product quality testing are in line with the national standard requirements.（4）The best formulation of Bacillus velezensis UB201712 aqueous suspension was obtained through the screening and optimization of microbial compounding additives:the main active ingredients were Bacillus subtilis and tea saponin,the dispersant was sodium lignin sulfonate（3.6%）,the wetting agent was Tween-80（2.4%）,the stabilizer was dipotassium hydrogen phosphate（2%）,the antifreeze agent was propanetriol（6%）,the defoamer DT-135（0.1%）is the industrial defoamer,and the rest is water.The quality of the suspension product tests all meet the requirements of national standards.（5）Evaluation of the activity of the coating after inoculation with blue mold and blue mold in Nanfeng mandarin fruit.The results showed that the relative efficacy of wettable powder at a dose of 3.0 g/20 m L was 83.3%and 76.7%against citrus blue mold and green mold,respectively.Relative efficacy of 77.8%against citrus blue mold at a dose of 108cfu/m L of Bacillus velezensis in aqueous suspension;the relative efficacy of the aqueous suspension against citrus green mold was 72.8%at a dose of 109 cfu/m L of Bacillus Bellesiosus. |
