Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2006
Publication Date: August 20, 2007
Citation: Medrano, E.G., Esquivel, J.F., Bell, A.A. 2007. Transmission of cotton seed and boll rotting bacteria by the southern green stink bug (Nezara viridula L.). Journal of Applied Microbiology. 103:436-444. Interpretive Summary: In recent years, a formerly unobserved seed and boll rot of cotton has caused yield losses ranging from 10 to 15%. Originally reported in South Carolina, the disease has since spread to fields throughout states of the southeastern Cotton Belt. The exterior of diseased bolls appear normal, but cross-sections of the immature, green fruit reveal brown-dense lint and rotted seeds. Previously, we determined that pathogenic bacteria are capable of reproducing these disease symptoms. Our disease model involved an experimental exposure method of injecting the disease-causing bacteria into cotton bolls. In the current report, we demonstrate that a major insect pest of cotton (the southern green stink bug) is capable of transmitting bacterial pathogens during feeding on cotton bolls. This work assists in understanding the dynamics of the disease process in the field and will ultimately assist in developing disease avoidance/treatment strategies.
Technical Abstract: The aim of this study is to determine the ability of the southern green stink bug (Nezara viridula L.) to transmit an opportunistic Pantoea agglomerans strain into unopened, green cotton (Gossypium hirsutum) bolls. Southern green stink bug (SGSB) colonies were reared on fresh green beans in the laboratory. A P. agglomerans variant resistant to rifampicin (strain Sc 1-R) was used as the opportunistic cotton pathogen. Adult insects were individually provided green beans that were sterilized and then soaked in either sterile water or a suspension of strain Sc 1-R. Insects were individually caged with an unopened greenhouse-grown cotton boll. After two days, live SGSB were collected, surfaced sterilized, ground and dilution plated on non-selective media and media amended with rifampicin (Rif). Exterior and interior evidence of feeding on bolls was recorded two weeks after exposure to insects. Seed and lint tissue were harvested, ground, then dilution plated on media with and without Rif. Bacteria were recovered on non-selective media from all insects, and from seed and lint with signs of insect feeding at concentrations ranging from 102 to 109 CFU g-1 tissue. The Sc 1-R strain was isolated only from insects exposed to the marked strain and from seed and lint of respective bolls showing signs of insect feeding. Evidence of insect feeding on the exterior wall of the carpel was not always apparent (47%), whereas feeding was always observed (100%) on the interior wall in association with bacterial infections of seed and lint. Southern green stink bugs readily ingested the opportunistic P. agglomerans strain Sc 1-R and transmitted the pathogen into unopened cotton bolls. Infections by the transmitted Sc 1-R strain caused rotting of the entire locule which often masked internal carpel wounds incurred by insect feeding. Bacteria were recovered from obvious penetration points by insects not exposed to the pathogen, but locule damage was limited to the area immediately surrounding the feeding site (ca 3 mm).