| In this study, we used plate confrontation and haemocytometer counts to screen an endophytic fungus (Fusarium sp. E5) that inhibited the growth and sporulation of Fusarium oxysporum f. sp. Niveum (FON) in combination with B6 (Ceratobasidum stevensii) screened by predecessors of our group. We also used single-factor and orthogonal experiments to screen micro-fertilizers, including 1 ppm iron,10 ppm manganese,0.1 ppm boron, and 0.01 ppm copper, that inhibited the growth and sporulation of FON. Finally, the fungicide Duofu also inhibited the growth and sporulation of FON according to growth rate and haemocytometer counts. These screenings provided the basis for work on alleviating obstacles to continuous cropping of watermelon by combining biological control, fertilizer, and chemical pesticides.The results of pot experiments showed that watermelon yield increased after the application of the endophytic fungi. The combined effects of both B6 and E5 were better than individual treatments with either; total output increased by 29.0%. The effects were significantly better after micro-fertilizer enrichment, when total output increased by 15.6%. The activities of superoxide dismutase, peroxidase, and catalase were enhanced, while disease incidence and the disease index decreased after the application of endophytic fungi. Again, the combination of B6 and E5 had a more substantial effect; disease incidence decreased by 31.5%. To optimize the microbial flora, the combined treatment with B6 and E5 was better than individual applications of either, while the effects of micro-fertilizers were not obvious. Shortly after the application of fungicide, the quantity of soil microorganisms decreased. Later the amounts of actinomycetes and other bacteria were partially restored, but the quantities of F. oxysporum and other fungi were not. The activities of sucrase, urease, and polyphenol oxidase were enhanced after the application of endophytic fungi, with the combination of B6 and E5 better than either alone. Micro-fertilizers had no obvious effect. The activities of soil enzymes were weakened to some extent. In conclusion, fertilizer combined with endophytic fungi (B6 and E5 together), micro-fertilizer, and fungicide offers an effective method to relieve obstacles to the continuous cropping of watermelon by optimizing the soil microflora, enhancing soil enzymes, decreasing the quantity of pathogens, increasing watermelon biomass and yield, and enhancing plant growth and resistance.The endophytes B6 and E5 can control the growth of FON, so we studied this antagonism using dual culture and antibacterial tests. The results showed that an inhibition zone appeared in dual culture between E5 and FON, but not between B6 and FON. However, we found that B6 could grow along the FON mycelia by forming appressoria-like structures, which inhibited the growth of but did not kill FON.The results of the antibacterial experiment demonstrated that the volatile substances secreted by B6 and E5 were antagonistic to the growth and sporulation of FON. The number of FON mycelium branches were reduced when exposed to the volatile substances of B6. In addition, an inhibition zone appeared in the antibacterial experiment using an ethyl acetate extract of sterile culture medium of E5. Next, we analysed the volatile substances and the ethyl acetate extract of E5 by gas chromatography-mass spectroscopy. The results showed that the volatile substances contained eight main ingredients, including six alkanes and one alcohol (4-methyl-l-pentanol); the ethyl acetate extract contained seven main ingredients, including one alcohol (2-phenylethanol). Finally, we studied the inhibition of FON by the two alcohols. The results showed that 4-methyl-l-pentanol and 2-phenylethanol both inhibited the growth of FON with EC50 of 0.002 and 3.51 μL/mL, respectively.
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