Population Dynamics And In Vitro Antagonistic Action Of Endophytic Bacteria In Tobacco Plants

Endophytic bacteria are ubiquitous in most plant species, residing latently or actively colonizing plant tissues locally as well as systemically, and do not visibly harm the plant. In this study, the population dynamics and biodiversity of endophytic bacteria from seeds, roots, stems and leaves of seven tobacco cultivars were examined at different plant developmental stages, and the antagonistic activities of the endophytic bacteria against four tobacco fungal pathogens in vitro were also examined. The results are as follows:1. Total seven genera (Bacillus, Xanthomonas, Envinia, Agrobacterium, Serratia, Flavobacterium, Pseudomonas) were isolated from plants of the seven tobacco cultivars, while Serratia was not detected in plants of the cultivar NC89, but it was detected just from recuperating stage to flourishing stage in all the other cultivars. Among the seven isolated bacteria genera, Bacillus and Agrobacterium were detected in seeds, and also detected at all the developmental stages of all cultivars.2. The dynamics of endophytic bacteria at different growth stages.The populations and flora of endophytic bacteria increased from seed to emergence stage,quickly, but decreased by a wide margin from emergence stage to crossing stage, and the population did not vary significantly until recuperating stage. During recuperating stage, all the seven genera of bacterial were detected, and the populations increased sharply from this stage.3. The dynamics of endophytic bacteria in tobacco roots, stems and leaves:Bacteria population densities were extremely variable in different tissues. The roots had the greatest population of endophytic bacteria , followed by in stems and leaves. In addition, the flora in stems could be also detected in roots, however, some flora in leaves could not be detected in roots and stems.4. The dynamics in different stages: The populations were significant difference in different stages to a certain extent in seven tobacco cultivars, while the flora was not significant difference. Though Serratia was not detected in NC89, the isolation rate of Serratia was also very low in the other cultivars.5. The survey of endophytic bacteria in different soil textures: The population was greater in sandy soils than in soils with low sand components, but the flora was more abundant in soils with low sand components. The population and flora were almost consistent in leaves, but showing significant difference in roots and stems at different growth stages.6. Endophytic bacteria were recovered in tobacco roots at mean population densities ranging from 2.0xl04to 1.0xl08cfu/g-fw. 1.9xl03 to 3.0xl07 cfu/g-fw in stems, and 6.3xlCr to 6.8xl06 cfu/g-fw in leaves, respectively. The average bacterial populations of whole plants ranged from 7.6x103 to 1.2xl07 cfu/g-fw.7. A number of 829 bacterial isolates were obtained from the seven tobacco cultivars. All the isolates were tested by duel culture for their antagonisms against using Botrytis cinerea, Phytophthora parasitica var. nicotianae, Alternaria allernata, and Colletotrichum nicotianae. The results showed that 61 isolates were antagonistic against Botrytis, 38 isolates against Phyophthora, 52 isolates against Alternaria. and 55 isolates against Colletotrichum. Some isolates from the roots, stems and leaves were shown antagonistic against all the four pathogens.