Ear migration in attached and detached sweet corn ears.

Authors: Yates, Ida; SPARKS, DARRELL - HORT./UGEORGIA, ATHENS

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2006
Publication Date: 12/1/2006
Citation: Yates, I.E., Sparks, D., Glenn, A.E. 2006. Ear migration in attached and detached sweet corn ears. Journal of the American Society for Horticultural Science. 163:157-161.

Interpretive Summary: The fungus F. verticillioides colonizes corn kernels causing mycotoxin production with harmful, and often fatal, effects to human and animal health, as well as plant disease. The fungus grows within the corn plant without producing toxins or causing disease until external factors, such as pests or other plant stress conditions intervene. Understanding the interaction of the corn plant with the fungus is essential to developing strategies to prevent the diseases and to eliminate mycotoxins from our food chain. The purpose of the current research was to analyze the distribution of F. verticillioides in corn kernels following an external application of a genetically transformed fungus or water compared to the collective F. verticillioides population of the fungus during a three-year field study. The fungus was applied through the shuck and silk at two stages of development, green silks versus brown silks. The F. verticillioides used for inoculation carried foreign genes detectable by growth and enzymatic staining. The collective population of F. verticillioides was determined by incubating kernels on a medium specific for the fungal species. The results demonstrated that 75% of the kernels were colonized by of F. verticillioides by analyzing the collective F. verticillioides population regardless of position at the top, mid, or base of the ear in ears that were either non-inoculated or inoculated with water. Only by analyzing for the genetically transformed fungus F. verticillioides was the impact of inoculation site apparent. Kernel inoculations through the silk resulted in a higher percentage of the transformed fungus at the top than those inoculated through the shuck. Likewise, a higher percentage of F. verticillioides was present in kernels at the mid section for ears inoculated through the shuck at the mid length of the ear. In conclusion, wounding caused by inoculation of water did not increase the collective F. verticillioides population. However, differences were identified in the site of inoculation following analyses for the transformed fungus. Thus, analysis of the collective F. verticillioides population may not provide accurate estimation of elements regulating F. verticillioides distribution and colonization.

Technical Abstract: Kernels of corn, Zea mays L., are colonized by Fusarium verticillioides and may result in mycotoxin production with harmful, and often fatal, effects to human and animal health, as well as plant disease. The fungus grows as an endophyte within the corn plant without producing toxins or causing disease until external factors, such as pests or other plant stress conditions intervene. Determining growth and development factors of the corn plant regulating this metamorphic relationship is essential to developing strategies that prevent diseases and eliminate mycotoxins from our food chain. The purpose of the current research was to analyze the distribution of F. verticillioides in corn kernels from ears inoculated with F. verticillioides RRC PATg, a transformant with a selection gene, hph, for hygromycin resistance (hygr) and a reporter gene, gusA, coding for ß-glucuronidase (GUS) or water compared to the collective F. verticillioides population of the fungus under field conditions. The fungus was applied through the shuck and silk at two stages of development, green silks versus brown silks. The collective population of F. verticillioides was determined by incubating kernels on a medium specific for the fungal species. The results demonstrated differences among treatments were apparent only by analyzing for the genetically transformed fungus, not the collective F. verticillioides population. Percentage colonization in kernels analyzed decreased from the top to the bottom of the ear following inoculation through the silks, regardless of developmental stage. However, for ears inoculated though the shuck at the mid point of the ear, the kernels from the mid section had the highest colonization. Kernels from the top and bottom were equally colonized. In conclusion, the collective F. verticillioides population is of such magnitude that differences in treatments was masked and became apparent only following analyses for the genetically transformed isolate.