Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Sugarcane (inter-specific hybrids of Saccharum) is grown largely under long-term monoculture production in Louisiana. This can lead to a complex problem termed "yield decline" that results in poor root health and reduced productive capacity of sugarcane. This problem has been documented to be a limiting factor for sugarcane production in diverse regions, including Louisiana, Hawaii, Jamaica, and Australia. Previous work showed that biological factors affect root health and contribute to yield decline. The objectives of this study were to increase our understanding of microbial communities in sugarcane soils, to determine if there are differences in microbial communities associated with sugarcane roots in soil with and without a sugarcane cropping history, and to provide information on possible changes in the microbial communities resulting from monoculture that may contribute to yield decline.

To achieve these objectives, two approaches were used for comparing culturable organisms in soil microbial communities from soil with and without a sugarcane cropping history, and methods were adapted to reliably obtain DNA from soil microbial communities for molecular comparisons. In one approach, colonies grown on different types of culture media were quantified and characterized. In the other approach, sole carbon source utilization profiles (SCSUP) of soil communities grown in Biolog(tm) GN2 microplates were compared. Comparisons of the numbers and types of microorganisms that grew on various culture media demonstrated that differences exist between microbial communities associated with sugarcane roots in Louisiana soils with and without a recent sugarcane cropping history. The differences in community functional diversity detected by SCSUP supported the differences found in types of microorganisms isolated on selective media. The SCSUP results showed that differences in community functional diversity exist between sites in soils with a long-term sugarcane cropping history in common.

Methods for DNA extraction and polymerase chain reaction (PCR) amplification were optimized for sugarcane soil microbial community samples from Louisiana. This will allow molecular characterization of sugarcane rhizosphere microbial communities in the future.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jeffrey W. Hoy