| Maize（Zea mays L.）is an important grain crop in China,however,maize production and quality have been severely influenced by stalk rot,one of the most widespread and destructive soil-borne diseases.At present,planting resistant varieties and applying chemical fungicides could manage maize stalk rot.However,breeding disease-resistant varieties is time-consuming and long-time use of chemical pesticides has caused environmental pollution and ecological imbalance.Therefore,it is particularly important to explore new strategies to control stalk rot that both have excellent control effects and environment safety.As an environmentally friendly,efficient and non-toxic control measure,biological control plays an increasingly important role in controlling plant diseases.Among them,Bacillus has been favored for its unique biological characteristics and remarkable biocontrol potential.In this study,an antagonistic bacterial strain,TA-1,showing significant inhibition against Fusarium graminearum,was isolated from maize rhizosphere soil samples,and the specific species of it was identified based on morphological and biochemical characterization as well as molecular biological identification.The inhibitory activity of TA-1 fermentation broth was determined,and the ultrastructure of the pathogenic mycelia was observed after the action of TA-1.At the same time,the control effect of TA-1 on maize stalk rot and maize growth was evaluated by greenhouse pot experiments and field trials.In addition,the lipopeptide antibiotics produced by TA-1 were analyzed and identified to explore their biocontrol mechanism and aimed to provide a theoretical basis for reducing the use of chemical agents and sustainable development of maize industry.The results of the study were summarized as follows:1.Antagonistic bacteria TA-1 was finally identified as B.methylotrophicus through the colony morphological observation,physiological and biochemical characteristics determination,as well as phylogenetic tree based on 16S rRNA and gyrB gene sequence analyses.2.The results of the dual-culture assay showed that TA-1 had a strong inhibitory effect on F.graminearum with the inhibition zone ranged from 10 to 15 mm.Different concentrations of TA-1 fermentation broth on mycelial growth of F.graminearum was determined and the results showed that with the increase of TA-1 concentration,growth of F.graminearum mycelia was gradually inhibited.When the concentration was 108 CFU mL-1,the mycelial inhibition rate reached a maximum of 86.32%.3.Greenhouse pot experiments showed that TA-1 significantly reduced the incidence and disease index of maize stalk rot.When the fermentation broth concentration increased from 104 CFU mL-1 to 108 CFU mL-1,the incidence of disease was reduced from 55.00%to11.67%,while the incidence in the control group reached 88.3%.Control effect reached86.79%when the fermentation broth concentration was 108 CFU mL-1.4.The results of field trials for two consecutive years showed that different concentrations of TA-1 fermentation broth can significantly reduce the incidence of maize stalk rot,showing a good control effect on the disease.In addition,compared to the control,after treatment with TA-1 fermentation broth,plant height,stem diameter,and yield of maize increased by 19.2%,27.8%,and 26.2%,respectively.It is further confirmed the preventive and promotive effects of the biocontrol strain TA-1.5.TEM observations revealed that strain TA-1 can destroy the cell structure of F.graminearum and caused cell degradation.In addition,it can also lead to degradation and loss of intracellular organelles,resulting in cell necrosis.6.Matrix-assisted laser desorption/ionization-time of flight mass spectrometry（MALDI-TOF MS）was used to identify the antibacterial substances produced by TA-1.The results showed that the lipopeptide compound Surfactin and Iturin were produced after TA-1fermentation,this may be the main biocontrol mechanism in controlling maize stalk rot. |
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