Abstract:[Background] Sclerotinia rot caused by Sclerotinia sclerotiorum is a major disease affecting the yield of sunflower and has occurred frequently in Inner Mongolia and Gansu of China in recent years. [Objective] In order to discover antagonistic strains and effective methods for the biocontrol of sunflower sclerotinia rot. [Methods] The microorganisms in the rhizosphere soil of healthy sunflower plants were isolated by dilution plating method with 4 different media, and then plate confrontation experiments were conducted to select the strains with antagonistic effects on S. sclerotiorum. The selected antagonistic strains were then tested for the control effect with detached leaves. They were identified based on the morphological characteristics, physiological and biochemical properties, and 16S rRNA gene sequence analysis. Finally, we mixed these strains at different ratios into different microbial inoculants for pot experiment to determine the in vivo control effects. [Results] A total of 142 strains of bacteria were isolated from the soils, among which 12 antagonistic strains with an obvious inhibition zone were screened out. Bacillus sp. NM63, JQ134, J7, J33, and Streptomyces sp. Z9 and ZX6 exhibited the inhibition zone diameters greater than 25 mm and significant control effects in detached leaves. Strains NM63, JQ134, J7, Z9, J33, and ZX6 exhibited the control effects of 79.06%, 74.10%, 70.72%, 67.83%, 65.11%, and 57.11% on potted sunflower seedlings, respectively. The microbial inoculants I and II prepared with strains Z9, NM63, JQ134, and J7 mixed at the ratios of 1:1:1:1 and 1:2:2:1 had the control effects of 81.43% and 85.88%, respectively, for potted sunflower. [Conclusion] The antagonistic strains with strong inhibitory effects on S. sclerotiorum were screened out and identified, and the compound microbial inoculant II had good performance in the prevention and treatment of sunflower sclerotinia rot.
