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Title: Fusarium verticillioides dissemination among corn ears of field-grown plants

Author
item Yates, Ida
item SPARKS, DARRELL - HORTICULTURE/UGA,ATHENS

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2007
Publication Date: 3/1/2008
Citation: Yates, I.E., Sparks, D. 2008. Fusarium verticillioides dissemination among corn ears of field-grown plants. Crop Protection. 27(3-5):606-613.

Interpretive Summary: A fungus, Fusarium verticillioides, grows in the corn plant. The fungus may cause diseases to the corn plant and synthesis of toxins known as mycotoxins in corn kernels. Diseases may reduce crop production and mycotoxins may cause harmful diseases in humans and animals eating contaminated corn and/or corn products. Interactions between the corn plant and F. verticillioides must be understood to develop strategies for prevention of corn plant disease and elimination of mycotoxins from our food chain. The purpose of this research was to analyze the field distribution of F. verticillioides from corn ears inoculated with F. verticillioides PATg. This particular fungus has been modified in the laboratory to carry two foreign genes, which may be used to positively identify the fungus growing in the corn plant. Corn ears were inoculated through either the shuck or the silk channel at two stages of development, green silks and brown silks. Inoculated ears were harvested at kernel maturity. In addition, non-inoculated ears were collected from plants adjacent to those with inoculated ears. Kernels were harvested from the middle portion of the ear and analyzed for the presence of F. verticillioides PATg by screening for the two foreign genes. One of the genes analyzed caused the fungus to be resistant to the antibiotic, hygromycin. Kernels are incubated on media containing hygromycin and screened for F. verticillioides colonization based on the appearance of fungal growth. The other gene caused the fungus to synthesize an enzyme which can be detected by stains. The majority of kernels from F. verticillioides-inoculated ears were positive for F. verticillioides colonization based on the appearance of fungal growth on the hygromycin assay. In contrast, ' 3% of the kernels from non-inoculated and water-inoculated ears were positive. The fungal growth from 66% of the kernels from F. verticillioides PATg-inoculated ears stained positive for the enzyme. Fungal growth from all kernels of non-inoculated ears was negative for the enzyme and only 7% of that isolated from kernels of water-inoculated ears. In summary, distribution of F. verticillioides PATg was minimal from plant to plant under field conditions existing in Georgia during the growing seasons of 2001, 2002, and 2003. Based on enzyme activity, the only evidence for F. verticillioides distribution was from a few ears inoculated with water through the silk during the green silk stage of development. Perhaps, mechanical injury during inoculation provided an entry site for the spores of F. verticillioides PATg dispersed by factors, such as rain or wind.

Technical Abstract: Consequences of the fungus, Fusarium verticillioides (Sacc.) Nirenberg (synonym F. moniliforme Sheldon) (teleomorph, Gibberella moniliformis), colonizing kernels of maize, Zea mays L., may be plant disease and/or mycotoxin production. Plant disease may reduce crop production and mycotoxins may cause harmful, and often fatal, effects on humans and animals. Understanding the dynamics between the maize plant and F. verticillioides is essential for developing strategies to prevent diseases of corn plants and eliminate mycotoxins from our food chain. The purpose of the current research was to analyze the field dissemination of F. verticillioides from corn ears inoculated with F. verticillioides PATg, a transformant with a selection gene, hph, for hygromycin resistance (hyg-r) and a reporter gene, gusA, coding for ß-glucuronidase (GUS). Corn ears were inoculated through either the shuck or the silk channel at two stages of development, green silks and brown silks. The average expression of hyg-r was 66% and GUS was 96% for mycelia emerging from kernels of ears inoculated with F. verticillioides. Mycelia resistant to hygromycin appeared in cultures of kernels from non-inoculated and water-inoculated ears, but only at less than 3%. However, none of the mycelia stained positive for GUS in kernels originating from non-inoculated ears and only 7% of those isolated from kernels of water-inoculated ears. Thus, dissemination of F. verticillioides PATg was minimal from plant to plant under field conditions existing in Georgia during the growing seasons of 2001, 2002, and 2003. The minimal dissemination occurred was restricted to a few ears inoculated with water through the silk during the green silk stage of development. Perhaps, the mechanical injury during inoculation provided an entry site for the spores of F. verticillioides PATg dispersed by abiotic factors, such as rain or wind.