1. Evaluation of Maize Inbred Lines for Resistance to Aspergillus and Fusarium Ear Rot and Mycotoxin Accumulation USDA-ARS Corn Plant Host Resistance Research Unit, Mississippi State, MS W. Brien Henry, W. Paul Williams, Gary L. Windham, and Leigh K. Hawkins. USDA - ARS Corn Research Objectives: The objectives of this study were: (1) to determine if a select group of inbred lines were resistant to aflatoxin and fumonisin accumulation in grain and (2) to determine the relationship of ear rot with aflatoxin and fumonisin contamination. Materials and Methods: Experiments were conducted in 2007 and 2008 on 20 corn inbreds of varying aflatoxin susceptibility. Ears were inoculated with toxigenic fungal strains of A. flavus (NRRL 3357) and a wild- type strain of F. verticillioides isolated from corn kernels grown at Mississippi State, MS. Ears were hand harvested, rated for rot, shelled, ground and mycotoxin levels were determined with the VICAM AflaTest®. 1. 2. 3. Conclusions: 1. There was a significant relationship between aflatoxin and fumonisin accumulation (r = 0.61; p = 0.004). 2. Several lines were highly resist to both aflatoxin and fumonisin accumulation Mp317, Mp313E, and Mp717. 3. Low rot does not necessarily mean low toxin (Ga209 aflatoxin) and high rot does Rot Data : Ear rot measured in cm 2 was significantly correlated to toxin production for both fumonisin (p = 0.0002; r = 0.74) and aflatoxin (p = 0.004; r = 0.61). Ear rot measured with the (1-9) visual rating scale provided slightly higher toxin correlations of (p = 0.0001; r = 0.76) and (p < 0.0001; r = 0.83) for fumonisin and aflatoxin, respectively. Aflatoxin & Fumonisin: Mp317 Mp313E Mp717 } Several lines were identified as low rot and low toxin producers for both aflatoxin and fumonisin Mp494 High rot but relatively low toxin production? Published: Agron. J. 101:1219–1226 (2009). Abstract: Mycotoxin contamination in corn grain is a worldwide threat to both human food safety and animal feed ingredients. A select group of inbred corn lines was evaluated in field trials for mycotoxin accumulation in grain and ear rot caused by Aspergillus flavus and Fusarium verticillioides. Our goal was to identify lines resistant to both fungi. In separate tests, 20 inbred lines were inoculated with either A. flavus or F. verticillioides. After harvest, ears were rated for rot and levels of aflatoxin or fumonisin contamination were quantified. Aflatoxin resistant inbred line Mp717 had the lowest levels of fumonisin contamination. Inbred line Mp317 has previously demonstrated F. verticillioides kernel infection had low levels of aflatoxin contamination. F. verticillioides and A. flavus ear rot measured in (cm 2 ) was significantly correlated to toxin production for both fumonisin (p = 0.0002; r = 0.74) and aflatoxin (p = 0.004; r = 0.61), respectively, indicating that inbreds exhibiting aflatoxin resistance may also be good sources of fusarium resistance. Our method of quantifying ear rot may also be used to rapidly screen lines for A. flavus resistance and subsequent aflatoxin accumulation in preliminary evaluations. Acknowledgments The authors thank research technicians Alan Hames, Paul Buckley, Mike Alpe, Gerald Matthews Jr., Gregg Flint, Jack Haynes, and LaDonna Owens for assistance with plot establishment, harvesting, toxin analysis and data collection. We also thank Dr. Dennis Rowe of Mississippi State University for his statistical assistance. Means in a column followed by the same letter do not differ at P<0.05 (Fisher’s Protected LSD). †Means for aflatoxin or fumonisin concentration were transformed [ln (y+1)] prior to statistical analysis, and tests of significance were performed on transformed means before converting back to the original scale. ‡Area of ear rot was measured on 10 ears after harvest using clear plastic grid marked in 1–cm 2 increments. §Percentage of ear rot was rated on 10 ears using a scale of 1 (no rot) to 9 (fully rotten ear). Table 1. Means for aflatoxin and fumonisin accumulation, ear rot, and ear ratings for 20 maize inbred lines inoculated with Aspergillus flavus or Fusarium verticillioides at Mississippi State in 2007 and 2008. Figure 2. A. flavus and F. verticillioides inoculation Figure 3. Ear rot with respect to year, inbred, and fungus. Figure 4. Determining ear rot with a plastic grid Figure 1. Aspergillus and fusarium ear rot of 20 inbred lines measured both in square centimeters and with a 1 to 9 rating scale with respect to toxin production in 2007 and 2008. 4. not necessarily mean high toxin (Mp494 aflatoxin). 4. Ear rot could be used for a first cut to reduce the total number of lines that are subsequently screened with additional techniques, saving time and money and allowing more lines to be screened for resistance to mycotoxin accumulation in grain.