| Selenium Melon is an important economic crop in Ningxia.Because of the climate and environment,the pressed sand planting mode of heat preservation and water conservation is usually adopted.The watermelon planted contains Selenium and other trace elements,so it is called Selenium Melon.The long-term continuous cropping of Selenium Melon led to the change of soil microbial community structure,which led to the decrease of soil fertility and the serious disease of watermelon Fusarium wilt.Biological control is the most promising way to control Fusarium wilt of watermelon.At present,there are few reports on the effects of soil microbial diversity and biological control of Selenium Melon continuous cropping in Ningxia.In this study,the soil microbial community structure of Selenium Melon continuous cropping in Zhongwei City,Ningxia was analyzed,and the strains antagonistic to Fusarium oxysporum f.sp.niveum,the pathogen of watermelon Fusarium wilt,were screened from the continuous cropping soil.The culture conditions of antagonistic bacteria were optimized with biological sulfonate as the main nutrient source,and liquid antagonistic agents were obtained by fermentation and applied to Selenium Melon soil in continuous cropping to study the changes of soil microbial community structure after application.To verily the control effect of the bacterial agent.The main conclusions are as follows:(1)Continuous cropping of Selenium Melon changed soil nutrient content and soil microbial community structure.There were some differences in soil nutrient content among different years of continuous cropping.After continuous cropping,the content of total nitrogen,phosphorus and potassium did not change significantly,but the contents of available potassium,available phosphorus and alkali-hydrolyzable nitrogen decreased,and the soil pH value was higher than that of non-continuous cropping soil.The soil fungal and bacterial diversity and species richness were different in soils with diffeerent continuous cropping years,and the fungal community diversity and species richness increased at first and then decreased with the increase of continuous cropping years,and the fungal diversity and species richness were the highest at 15 years.Bacterial diversity decreased with the increase of continuous cropping time.In the soil microbial community structure,the composition of the dominant phylum is similar,and Fusarium and Bacillus are the dominant genera in continuous cropping soil.The contents of total phosphorus,alkali-hydrolyzable nitrogen and available phosphorus were the main factors affecting soil fungal community,while organic matter and available potassium were the main factors affecting the composition of bacterial community in Selenium Melon continuous cropping soil.The continuous cropping obstacle of Selenium Melon is not caused by the change of soil nutrient content,but by the change of microbial community structure in soil.(2)Fusarium oxysporum f.sp.niveum was used as pathogen indicator,14 strains with good antagonistic activity were screened,and 2 strains XS-4 and XS-20-15,which were not antagonistic to each other and had good antagonistic effect against pathogen indicator were further screened.XS-4 was identified as Bacillus subtilis and XS-20-15 was identified as Bacillus velezensis.(3)The antagonistic bacteria were cultured in the culture medium with biosulfonate as the main nutrient source.After 14 hours of shaking flask culture,the cell concentrations of XS-4 and XS-20-15 reached 1.57 X 108 CFU/mL and 1.61 X 108 CFU/mL,respectively.(4)XS-4 and XS-20-15 were fermented with optimized biosulfonate culture medium,and antagonistic agents were prepared and applied to Selenium Melon continuous cropping soil.The results showed that the soil enzyme activity increased after the application of bacterial agent,and the effect of bacterial agent on the fungal community structure in continuous cropping soil was significant,and the abundance of Fusarium decreased with the increase of bacterial concentration.However,with the extension of time after application,the abundance of Fusarium in the tested soil increased,indicating that the antagonistic effect of bacterial agent on Fusarium was gradually decreased with the extension of application time.Compared with the change of fungal community in soil,the change of soil bacterial community was not significant after the application of bacterial agent.(5)The redundancy analysis between microbial community structure and environmental factors of soil samples from different treatments showed that at the genus level,soil polyphenol oxidase,soil catalase and soil alkaline phosphatase were the main environmental factors significantly affecting fungal community,and there was a significant negative correlation between Fusarium and soil polyphenol oxidase.Soil polyphenol oxidase,soil catalase and soil sucrase were the main environmental factors that significantly affected the bacterial community,and Bacillus had extremely significant positive correlation with soil polyphenol oxidase and significant positive correlation with soil sucrase.The results showed that the application of bacterial agent could not only play a direct antagonistic effect on pathogenic bacteria,but also reduce the abundance of pathogenic fungi in soil and increase the number of beneficial microorganisms. |
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