Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2006
Publication Date: 1/20/2007
Citation: Medrano, E.G., Bell, A.A. 2006. Role of Pantoea agglomerans in opportunistic bacterial seed and boll rot of cotton (Gossypium hirsutum) grown in the field. Journal of Applied Microbiology. 102:134-143. Interpretive Summary: An emerging disease of cotton called “South Carolina seed rot” was first noticed in 1999 when it caused significant yield losses in that state. The malady kills cotton seed and reduces fiber quality. Recently, infections of this type have spread throughout southeastern Cotton Belt States. However, the cause of the disease has not been identified. In the current study, we describe the recovery and identification of a bacterium called Pantoea agglomerans from diseased South Carolina bolls. Strains of P. agglomerans were determined to be capable of inflicting disease symptoms in greenhouse grown cotton that are comparable to natural infections observed in field grown bolls. This work provides important initial information and a focus for research geared towards minimizing or eliminating cotton seed and fiber losses due to infections by this newly identified disease agent.
Technical Abstract: In 1999, significant yield losses in South Carolina cotton resulted from a previously unobserved seed and boll rot that has since been reported in other southeastern states. Immature diseased bolls posseess a non-symptomatic exterior carpel; however, cross-sections reveal necrotic seed and discolored fiber tissue. In the current study, we report the isolation of Pantoea agglomerans from field collected immature, diseased bolls that were capable of causing comparable infefction symptoms in greenhouse grown cotton fruit. Spontaneously generated rifampicin resistant mutants of the suspect pathogens were used in disease tests. Resistance to the antibiotic was both stable and effective in differentiating between an inoculated rifampicin resistant strain, refampicin sensitive contaminants, and/or endophytes. A series of inoculation methods was tested at various boll developmental stages and plant sites. Field observed symptoms were mimicked by inoculating bolls, at two weeks post-anthesis, with a bacterial suspension. The demonstrated pathogenic isolates were categorized as P. agglomerans on the basis of phenotypic testing, fatty acid profiling, and 16s ribosomal DNA sequence analysis.