It has been accepted for many years that there is an interaction between plants

and the microbiological life that exists in soil. This interaction is particularly

important in the rhizosphere (Hiltner, 1904), where plant exudates directly feed the

microbial population, which in turn is responsible for nutrient cycling, production of

growth promoters, and occasionally development of pathogenicity. These factors are

important to plant health. However, the difficulties of studying such interactions in

the soil and the inability to grow the majority of soil microorganisms in the

laboratory have resulted in limited research in this area.

With the introduction of genetically modified (GM) crops into agricultural

production systems, public concern resulted in renewed interest and research into

the possible environmental consequences of growing GM Crops(Brookes and

Barfoot, 2005). This included the potential impact of GM crops on soil microbiology.

GM crops have the potential to influence soil microbiology through (i)the exudation

of transgenic proteins from the rootsystem, (ii)the release of transgenic proteins

from broken and dying roots, (iii) the incorporation of above ground plant material

into the soil, and (iv) differences in exudation chemistry (Gupta and Watson, 2004;

Knox et a1. , 2006; Saxena and Stotzky, 2001).

Between 2003 and 2006 we assessed the potential for GM cotton, expressing

either insecticidal Bt-proteins, glyphosate tolerance or both traits, to influence the

soil microbiota. The analysis of the rhizosphere microbiology showed some

differences, but none that were specifically identified as being caused by the

expression of the introduced transgenic material(Knox et a1. , 2004). The results did,

however, imply that cotton variety and family groupings were more likely to be

associated with the observed differences in the rhizosphere microbiota.

In this project we investigated the impact and significance of variety driven

alteration of rhizosphere microbiology for a number of Australian cotton varieties.