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The phyllosphere supports a tremendous diversity of microbes, which have the potential to influence plant biogeography and ecosystem function. Although biocontrol agents (BCAs) have been used extensively for controlling plant diseases, the ecological effects of BCAs on phyllosphere bacteria and the relationships between phyllosphere community and plant health are poorly understood. In this study, we explored the control efficiency of two BCA communities on bacterial wildfire disease by repeatedly spraying BCAs on tobacco leaves. The results of field tests showed that BCAs used in our study, especially BCA_B, had remarkable control effects against tobacco wildfire disease. The higher control efficiency of BCA_B might be attributed to a highly diverse and complex community in the phyllosphere. By 16S ribosomal RNA gene sequencing, we found that phyllosphere microbial community, including community diversity, taxonomic composition and microbial interactions, changed significantly by application of BCAs. According to the correlation analysis, it showed that wildfire disease infection of plants was negatively related to phyllosphere microbial diversity, indicating a highly diverse community in the phyllosphere might prevent pathogens invasion and colonization. In addition, we inferred that a more complex network in the phyllosphere might be beneficial for decreasing the chances of bacterial wildfire outbreak, and the genera of Pantoea and Sphingomonas might play important roles in wildfire disease suppression. These correlations between phyllosphere community and plant health will improve our understanding on the ecological function of phyllosphere community on plants. [ABSTRACT FROM AUTHOR]

Continuous cropping has become the most common system in intensive, modern agricultural production; however, obstacles often appear in continuous cropping patterns after a few years of use. There have been several studies about the impacts of continuous cropping on soil microbial, but few about differences between soil experiencing continuous cropping obstacles and those where such obstacles had been resisted. Here, after ten or twenty years of continuous tobacco cropping, we collected soil samples investigating discrepancies in soil property and bacterial community between soils experiencing continuous cropping obstacles and soils where the obstacles were resisted providing insight into preventing and controlling continuous cropping obstacles. Results showed that soil organic matter (SOM), available phosphorus (AP), total nitrogen (TN), nitrate-N (NO 3 −-N), and bacterial diversity of samples where continuous cropping obstacles had been resisted were significantly higher than those where continuous cropping obstacles were present. Besides, SOM, AP, TN, and Ammonium-N (NH 4 +-N) considerably affected the bacterial community. Among all variables, NH 4 +-N explained the largest proportion of bacterial community variation. Molecular ecological networks were used to putatively identify keystone taxa, including Acidobacteria Gp1 , Acidobacteria Gp2 , Acidobacteria Gp16, and WPS-1_genera_incertae_sedis. Their relative abundance significantly changed between the two conditions. Overall, our results indicate that decreases in soil nutrient content and bacterial diversity, and significant changes in some keystone taxa abundances may be important factors leading to increased soil-borne diseases and reduced tobacco production potential or quality. Thus, during agricultural production, we could regulate the stability of the soil-crop-microbial ecological system via crop rotation, intercropping, or the use of specialized bio-fertilizers and soil conditioners to mitigate continuous cropping obstacles. • The SOM, AP, TN, NO 3 −-N, and bacterial diversity of RCCO were significantly higher than CCO. • The SOM, AP, TN, and NH 4 +-N had a considerable effect on RCCO and CCO bacterial communities. • Soil NH 4 +-N explained the largest proportion of bacterial community variation. • The relative abundance of keystone taxa significantly changed between the two conditions. [ABSTRACT FROM AUTHOR]