Study on Foliar Microbes of Tobacco Varieties with Different Tolerant Levels to Herbicides

In order to investigate the quantity and herbicide tolerance of cultivatable microbes on leaves of tobacco varieties which have different tolerant levels to corn herbicides (atrazine and mesotrione), 12 tobacco varieties with different tolerant levels to two corn herbicides were cultivated and used as experimental materials. The leaf samples from the main growing stages including seedling stage, fast-growing stage and maturity stage were collected. The second leaf from the top was used for all the treatments. The plate counting method was used to study the number of cultured fungi, bacteria and actinomycetes. The toxic medium method was used to screen resistant bacterial strains to two corn herbicides. The 16S rDNA of obtained resistant bacterial strains in this experiment were sequenced and analyzed. The experimental results showed that the total numbers of cultured microbes including fungi, bacteria and actinomycetes were significantly different among different tolerant levels of tobacco (p<0.05). The microbial community composition on the leaves of tobacco varieties with different tolerant levels indicated that bacteria > actinomycetes > fungi. The numbers of bacteria and actinomycetes in the order from high to low was highly tolerant varieties, moderately tolerant varieties and highly sensitive varieties. The numbers of fungi from high to low: highly sensitive varieties > moderately tolerant varieties > highly tolerant varieties. Five bacterial strains highly resistant to the two corn herbicides were identified from the dominant bacteria strains isolated from highly tolerant varieties. The 16S rDNA sequences of the five highly resistant strains were compared and analyzed. The analysis results showed that the five strains all belong to Bacillus bacteria. There were large numbers of resistant microbes on tobacco varieties highly tolerant to the two corn herbicides. Therefore it is possible that resistant microbes play an important role in tobacco tolerance to herbicides.