| Fusarium wilt of bitter gourd is a typical vascular disease,one of the serious obstacles that affect the production of bitter gourd,and it is difficult to eradicate.In this study,the biocontrol bacteria with antagonistic activity to Fusarium oxysporum were screened from the rhizosphere bacteria isolated from different habitats.By studying the inhibitory activity against Fusarium oxysporum,the control effect on Fusarium wilt,and the colonization ability,the biocontrol potential of the two strains was explored,providing excellent resources for biological control on Fusarium wilt of bitter gourd.This study selected two biological strains of K18-5 and KH48-5 that could inhibitory activity to Fusarium oxysporum by screening.Both K18-5 and KH48-5 could inhibit spore germination and hyphae growth of Fusarium oxysporum.In pot experiment,the control effect of K18-5 and KH48-5 on Fusarium wilt was 75.27% and 69.11% respectively.K18-5 achieved the best control effect when the application concentration was 108 cfu·m L-1,and the times of treatment was applying the K18-5 for once when transplanting and applying twice after transplanting;KH48-5 achieved the best control effect when the application concentration was 108 cfu·m L-1,and the times of treatment was applying the KH48-5 for once when transplanting and applying once after transplanting.The morphological characteristics,physiological and biochemical characteristics and the homology analysis of the 16 S r DNA sequence of the 2 strains indicated that both the strains were belonging to Paenibacillus polymyxa.Both K18-5 and KH48-5 had good colonization ability in rhizosphere soil;the colonization density was measured by double-layered filter paper method in dish,and the colonization density was 2.45×104 cfu·cm-1 root and 4.60×103 cfu·cm-1 root respectively;in pot experiment,the colonization density of K18-5 and KH48-5 in the root of bitter melon kept stable at above 103 cfu·g-1;in field experiment,the colonization density of both K18-5 and KH48-5 remained stable above 103 cfu·g-1 in root and rhizosphere soil of bitter gourd in the whole growth and development stage.K18-5 and KH48-5 could colonize in the stem of bitter gourd.In addition,in the presence of pathogens,the colonization of biocontrol bacteria enhanced significantly and the colonization amount of non-susceptible plants was significantly higher than that of susceptible plants under the same treatment of biocontrol bacteria and pathogenic bacteria.The results showed that the colonization amount of biocontrol bacteria was one of the main factors for the control effect of biocontrol bacteria.Effects of biocontrol bacteria on roots and micro ecology of rhizosphere soil of bitter gourd In field experiment,K18-5 and KH48-5 could significantly increase the root activity of bitter gourd by 30.99%~102.94% and 23.93%~29.48% in the whole growth and development stages respectively;and could adjust the microecology of the rhizosphere soil of bitter gourd to a certain extant.K18-5 and KH48-5 could significantly increase the number of bacteria in the rhizosphere soil,while decreasing the number of fungi.In addition,K18-5 and KH48-5 increased enzyme activities significantly in rhizosphere soil of bitter gourd,the urease activity was increased by 27.65%~47.61% and 2.11%~8.65%,phosphatase activity was increased by 17.22%~32.10% and 9.35%~34.90%,the invertase activity was increased by 25.72%~71.36% and 16.05%~101.61% respectively.The crude extract of antifungal substances significantly inhibited the hyphae growth of Fusarium oxysporum,and the control effect of pot experiment was 72.73% and 68.18% respectively.In addition,the solubility,acid-base stability and thermal stability of the crude extracts were studied.The results showed that the crude extracts easily dissolved in polar organic solvents,and almost could not dissolve in non polar organic solvents.And the inhibitory activity of the crude extracts that were extracted from K18-5 was relatively stable when p H was 4.0~8.0 and temperature was 0?~120?.Besides,the crude extracts of KH48-5 could maintain the activity at a relatively stable level when the temperature was 20?~80?and p H was 4.0~10.0. |
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