Impacts Of Transgenic Insect-resistance Cotton On Diversity Of Rhizosphere Bacteria

In recent years, along with the spread and increasing growing area of transgenic cotton, its safety is more and more becoming concerns of scientists all around the world. Soil microorganism is an important component of agricultural ecosystem. The ecological safety assessment of soil microorganism that transgenic cotton impacts on soil microorganism populations is a very important item for the safety evaluation. The research of soil rhizosphere microorganism of transgenic cotton is of high significance not only in theory but also in practice. However, the special property of soil microorganism makes the research approach a little difficult to apply. Molecular techniques developed during the past decade are being used in this kind of research gradually. Denaturing gradient gel electrophoresis (DGGE) perhaps is a useful tool in analyzing the microbial diversity in soil. DGGE can reflect the diversity of soil microorganism more accurately comparing with the traditional methods. We used DGGE in combination with traditional plating method to study the populations of the rhizosphere microbes under the influence of Bt transgenic cotton, and hereafter is a brief results.Traditional method results showed that the total number of bacteria populations was positively related to the corresponding date of cotton growth stages, which began to rise at budding, quickly reached its peak at flowering stage, and decreased slightly later in wadding stage. In the same growth stage, transgenic cotton and non-transgenic cotton had large difference. The population of rhizosphere bacteria about the transgenic cotton SGK321 had difference with non-transgenic cotton Shiyuan321's in the whole stages except seedling period. And it reached a significant level. But the population of rhizosphere actinomycetes of transgenic cotton had difference with non-transgenic cotton Shiyuan321's in flowering, and it reached a significant level. For the transgenic cotton GK12, the population of the rhizosphere bacteria had difference with its parent Simian3 in budding and flowering. It reached a significant level. The population of the GK12's rhizosphere actinomycetes had difference with Simian3's in seedling and flowering. For the population of the rhizosphere bacteria, In the whole stages, SGK321 and Shiyuan321 had difference with GK12 and Simian3. For the population of the rhizosphere actinimycets, the change doesn't following any law. From the whole growing stage perspective, the impact that the growth of transgenic cotton caused on rhizosphere bacteria, is the biggest in budding and flowering, which caused on rhizosphere actinomycetes is the biggest in flowering.The diversity of the bacteria rhizosphere microbial was analysised by DGGE. The results showed: four varieties(SGK321 and Shiyuan321,GK12 and Simian3)and four stages, 16 soils samples had a lot of same bands. It means that the basic types of microorganisms that bands stood for may be represent in these samples. Most of detected bands with no illumination change in DGGE were likely to represent the indigenous microbes that were essential for constructing and stabilizing farmland microecological environment. But some bands changed, it performanced that the bands had or not, enhanced or diminished. It means that the bacteria had great changes in the different cotton varieties and different growing periods. Two pairs of transgenic cotton varieties (SGK321 and Shiyuan321, GK12 and Simian3) rhizosphere bacterial diversity were in the highest similarity at seedlings, for 77% and 74%, Budding and flowering periods were in the minimum similarity of 58%～60%, wadding stage similarity was not high, for 58% and 72%. The influence of the transgenic cotton's planting for the bacteria diversity was the smallest at seedling, and the biggest at budding and flowering. This would get the same results with which generated by the early traditional method.