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Title: Management of cotton rhizosphere-microbe interactions for sustainable/improved cotton
Authors: Knox, Oliver
Keywords: microbiological life in soil
cotton plants
microbial population
soil health
GM crops
Bt transgenic cotton
rhizosphere microbiota
extension and adoption
microbial communities
functional capabilities relating to N
fertiliser costs
best management practices
plant health
Issue Date: 30-Jun-2009
Publisher: CSIRO Entomology
Series/Report no.: ;CRC136
Abstract: The presence of an active interaction between plants and microbiological life in soil has been accepted for many years. This interaction is particularly important in the rhizosphere, where plant exudates and other rhizodeposits directly feed the microbial population, which in turn is responsible for nutrient cycling, production of growth promoters, disease suppression, agrochemical degradation and occasionally development of pathogenicity. These factors are important to plant health and productivity. However, the difficulties of studying such interactions in the soil and the inability to grow the majority of soil microorganisms in the laboratory (for example, at present <10% of microbial life in soil is cultured in the laboratory) have resulted in limited research in this area. Up to 40% of photosynthetically fixed carbon is released by plant root. With the introduction of genetically modified (GM) crops into agricultural production systems public concern resulted in renewed interest and research into the impacts of new varieties of cotton on plant growth, productivity and environmental health. (Gupta and Watson, 2004; Brookes and Barfoot, 2005). Results from the previous research indicated that although some differences exist between rhizosphere microbial communities of non-GM and GM crops, they were not specifically identified as being caused by the expression of the introduced transgenic material alone. The results did, however, imply that cotton variety groupings were more likely to be associated with differences in the rhizosphere microbiota. In this project, two years of field and laboratory trials were conducted to assess what level of influence cotton varieties have on their associated soil microbiota involved in key functions and if there might be potential to influence these as a management tool. Results demonstrated that there is a very strong relationship between the bacterial communities that develop in the cotton rhizosphere from the start of the season. Although there were seasonal based differences in the populations of rhizosphere microbial communities, a clear varietal separation was observed. Differences in the genetic and catabolic diversity of microorganisms between varieties suggest that rhizosphere microbial communities may be adapted to the quantity and quality of root exudates from cotton plants. The released plant products act as selective carbon and nutrient sources enriching a select group of microbial communities. These diverse microbial communities demonstrated shifts in several functional capabilities, particularly relating to N cycling e.g. N mineralization, free-living nitrogen fixation. This could form the basis for development of lower input and more biologically orientated and efficient cotton farming systems. With the current increases in fuel and fertilizer costs such systems are likely to be beneficial in the near future, but more work would be required to capitalise fully on this potential.
Appears in Collections:2009 Final Reports

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