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Infectivity titration dose response curves within Aspergillus flavus: A Case for Infection Specificity

Rebecca Sweany: Louisiana State University AgCenter

<div><em>Aspergillus flavus</em> contaminates corn and other oil-seed crops with carcinogenic aflatoxin. Soil <em>A. flavus</em> populations differ from crop populations. Among Louisiana soil and corn <em>A. flavus</em> populations, only six of 16 vegetative compatibility groups (VCG) infected corn. Infection ability of two soil VCGs and two frequent corn VCGs was assessed with a 2-year field infectivity titration experiment. Silks were dipped into doses of 1x10<sup>5</sup>, 10<sup>7 </sup>and<sup> </sup>10<sup>9</sup> conidia/ml for each VCG. To determine infection differences between VCGs, generalized linear models with logit link for binomial distribution predicted infectivity dose response curves (infected kernels/ear vs. dose). Dose response curves were not sigmoidal as expected, but u-shaped (parabolic). Dose response curves differed between soil and corn VCGs. Soil VCGs resembled inverted u-curves but the curve estimates were not statistically significant, indicating relatively low infection. Corn VCGs had statistically significant u-shaped curves, indicating greater infection than soil VCGs especially at 10<sup>9</sup>. When silks were inoculated with 10<sup>9 </sup>conidia, soil VCGs infected 6±s.e.3% and 8.2±2% of kernels and corn VCGs infected 17±3% and 12±3%. If dose was treated as a class variable, the most frequently isolated corn VCG infected more frequently than the other corn VCG in only one year. Though considered an opportunistic pathogen, certain strains are more frequently isolated from corn due to increased virulence on corn.</div>