| Volatile substances produced by Bcillus sp.have good antibacterial properties and environmental friendliness.They have been widely used in the prevention and control of postharvest fruit rot and plant diseases,and their application in grain anti-mildew have rarely been reported.In this paper,Bacillus strian producing anti-mildew volatile compounds were screened and identified,then,the components of their volatile substances were analyzed and identified,and compounds with strong anti-mildew effects on paddy rice were screened out.The broad-spectrum antifungal activity and the MIC and MBC for each tested mold of the screened compounds were studied.Finally,the anti-mildew effect of the compounds on paddy rice was explored under different conditions.The main results in the paper are as follows.(1)7 species of Bacillus were isolated from paddy rice and soil.A.niger was used as indicator bacteria and inhibitory rates on A.niger of these Bacillus were determined by flat plate buckle method.Among them,strains PW2 and SW5 had the highest inhibitory rates of 86%and 84%,respectively.Through morphological,playsiological and biochemical identification and 16S rDNA sequence analysis of the two strains,the strain PW2 was finally identified as B.subtilis and SW5 as B.velezensis.(2)The volatile substances produced by strains PW2 and SW5 were analyzed and determined through the SPME-GC/MS method,and 41 and 20 kinds of different components were obtained respectively,including alcohols,ketones,aldehydes,esters,phenols,acids,ethers,alkanes,alkenes,and many other compounds.7 kinds of compounds with high content and preliminary reports of antifungal activity were selected from these compounds for the study of the control effect of paddy rice mildew.It was found that 2-nonanone,2-decanone,phenethyl alcohol,2-undecone,2-tridecone,dodecanol and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate have a certain inhibitory effect on paddy rice mildew,and fumigation of acetophenone and p-cresol caused serious deterioration of paddy rice.While the color of paddy rice treated with isooctyl alcohol and isobutyric acid is normal,without any mildew phenomenon,and the overall prevention and control effect on paddy rice mildew is the best,and the inhibitory rate is significantly higher than that of other compounds(p<0.05),up to 99.92%and 99.85%respectively.(3)The study found that isobutyric acid and isooctyl alcohol have broad-spectrum antifungal effects on seven common harmful molds in paddy rice.The two-cell petri dish method was used to determine the MIC and MBC of isobutyric acid and isooctyl alcohol on 7 kinds of tested molds respectively.Among the 7 kinds of molds,F.graminearum is the most sensitive to isooctyl alcohol,and its MIC and MBC values are 20 μL/dish and 30μL/dish,respectively.Isooctyl alcohol at a concentration of 30 μL/dish can completely inhibit the growth of all tested molds except P.oxalicum;isobutyric acid also has a good anti-killing effect on seven kinds of tested molds,the MIC value of it on F.graminearum and R.pluvialis are both 10 μL/dish,and isobutyric acid at a concentration of not higher than 60 μL/dish can completely kill 6 kinds of tested molds except R.pluvialis.(4)Isobutyric acid and isooctyl alcohol were mixed in volume ratio of 1:1,1:2,2:1,the measurement results showed that the control effect of three mixtures on paddy rice mold counts and fatty acid value is not enhanced compared with that of using isooctyl alcohol or isobutyric acid alone under the same concentration conditions,indicating that there is no synergistic effect between isobutyric acid and isooctyl alcohol.But isooctyl alcohol and 1:2 mixture can control the fatty acid value while being highly effective in preventing mildew of paddy rice,therefore,the effect of fumigation treatment with isooctyl alcohol and 1:2 mixture on paddy rice mold counts and fatty acid value under different conditions was explored.It was found that the control effect of isooctyl alcohol and 1:2 mixture on mold number and fatty acid value of paddy rice with moisture content of 16.2%,20.0%,and 23.5%is very significant;when the fumigation temperature is 10℃,20℃ and 30℃,isooctyl alcohol can control the growth of mold counts and fatty acid value of paddy rice significantly,and 1:2 mixture can also inhibit the growth of paddy rice mold counts significantly at different fumigation temperatures,but it only can significantly control the increase of the fatty acid value of paddy rice when the fumigation temperature is 30℃;when the fumigation time is 3 d,5 d,7 d,isooctanol can significantly control the growth of mold counts and fatty acid value of paddy rice,and 1:2 mixture can inhibit the growth of paddy rice mold counts significantly at different times of fumigation,but it only can control the increase of fatty acid value of paddy rice significantly after fumigating 5 d and 7 d.Isooctyl alcohol and 1:2 mixture can effectively inhibit the increase of AFB1 and OT content in paddy rice.The preliminary quality evaluation of the tested paddy rice showed that the rice fumigated with isooctyl alcohol for 3 days is suitable for storage,while the corresponding control rice is mildly unsuitable.Isooctyl alcohol and isobutyric acid can significantly control the color change of the paddy rice,and they will not affect the odor of the paddy rice after fumigation as the fumigation time increases. |
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