| The tropical fruit post-harvest storage and transportation industry has become an important part of Hainan’s fruit and vegetable industry chain.The unique climatic conditions of Hainan area have bred many typical tropical fruits such as mango,papaya,banana,dragon fruit,lotus mist,litchi,longan,carambola,and so on.They hold the characteristics of variety,unique flavor,high nutrition,which are favored by consumers.However,the perennial high temperature and humidity environment provides favorable conditions for many postharvest pathogens to infect tropical fruits,and postharvest diseases frequently occur.Frequent use of chemical fungicides has made pesticide residues,pathogen resistance and many food safety issues increasingly serious.Chemical control is no longer feasible for a long time.Green and environmentally friendly biological control methods have become a more ideal choice for postharvest preservation and disease control of fruits and vegetables.In our research,a variety of tropical fruits in Hainan were selected as the materials,and 6 postharvest pathogens were isolated from the fruits rotted in natural.Based on the 6 indicator pathogens,a broad-spectrum strain N-1 were isolated from the soil of the lotus mist orchard.The biocontrol effect of N-1 was studied in vitro and in vivo respectively,and the antagonistic mechanism was preliminarily discussed.(1)Isolation,screening and identification of pathogens from postharvest fruits:6pathogenic fungi were isolated and purified from the diseased spots(the junction of disease and healthy)of carambola,longan and banana fruits,which were numbered as L-B1,L-B2,XJ-B1,XJ-B2,A-B2,and A-B3.Based on pathogenicity test of Koch’s law,morphological characteristics and molecular biological sequence analysis,they were identified as Fusarium incarnatum,Lasiodiplodia theobromae,Geotrichum candidum,Fusarium lateritium,Phomopsis sp.and Diaporthe phaseolorum,respectively.(2)Isolation,screening and identification of antagonists:9 antagonistic strains were isolated and screened from the samples of root soil or tropical fruit leaves in the lotus mist orchard.A antagonists biocontrol bacteria strain numbered N-1 stand out of the re-screening test,which was considered as the research object.After morphological,physiological and biochemical characterization,combined with 16S r DNA sequence analysis,N-1 was identified as Bacillus siamensis.Its preliminary biological characteristics showed that the most vigorous growth would be presented after being ultured for 27 h at 30°C and p H 7.0.(3)A comparative study on the broad-spectrum antagonistic ability of strain N-1and 9 antagonists stored in the laboratory:21 strains of tropical fruit postharvest pathogens were used as indicator fungi to determine the broad-spectrum antagonistic ability of 10 strains in vitro,24-well-plate test results showed that 7 broad-spectrum strains of LW,JM-1,TE-7,W-2,D,G,and N-1 were found to have antifungal activities against indicator pathogens.The growth of fungal mycelium inoculated with antagonists was inhibited to varying degrees.According to the classification of inhibition ability,it is found that only Bacillus siamensis(N-1)was capabile of inhibiting all indicator pathogens as"+++",and the pathogens hardly grow in the hole.Strain N-1 showed the best broad-spectrum antagonistic activity against 21 tested pathogens.(4)Studies on the mango and litchi fruits treated with antagonist N-1:The biological control test in vivo indicated that strain N-1 was capable of reducing the postharvest incidence and rot of the two fruits during storage,and inhibit postharvest browning of litchi fruits.The good fruit rate of litchi fruits treated with N-1 has been significantly improved(p<0.05).Compared with the control,strain N-1(10~8 CFU/m L)well maintained the physiological qualities of mango and litchi fruits during storage.strain N-1 delayed the hardness,the contents of TSS,TA and Vc of the two fruits to varying degrees.At the end of storage,the decrease of TSS and TA content in fruits was significantly delayed,especially the litchi fruits soaked with N-1,the Vc content could be maintained above 50 mg/100 g.(5)Preliminary study on the broad-spectrum antagonistic mechanism of biocontrol strain N-1:During the co-cultivation process,the volatile organic compounds(VOCs)produced by N-1 showed a significant inhibitory effect on the tested fungi.The analysis results of gas chromatography-mass spectrometry(GC-MS)combined with solid phase microextraction(SPME)showed that 15 diffusible compounds were secreted,and five of them were found to have properties in both inhibiting growth of hyphae and delaying conidial germination of the pathogens.The relative peak area of 1-Undecene can reach81.08%.Moreover,through Ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry(UPLC-QQQ-MS)analysis,the surfactin lipopeptide was speculated to be produced by antagonist N-1.The extracellular lytic enzymes,includingβ-1,3-glucanase,cellulase and protease released by N-1 were detected.The combination of different action mechanisms led to the broad-spectrum performance of B.siamensis to defend and attack pathogens in vivo and in vitro. |
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