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Influences of temperature and host on atoxigenic Aspergillus flavus isolates
P. FALKENBERG (1), P. J. Cotty (1). (1) United States Department of Agriculture - ARS, Tucson, AZ, U.S.A.

The extent to which crops become contaminated with aflatoxins depends on the composition of <i>Aspergillus</i> populations. In the current study, influences of temperature on production of conidia by <i>A. flavus</i> on Czapek agar, maize, soybean, and peanuts were quantified. Three isolates of <i>A. flavus</i>, one aflatoxin producer and two atoxigenic isolates, were examined.  Media composition influenced the temperature of maximum sporulation.  However, during individual growth both atoxigenics produced more conidia at 35 C than at 25 C on all three crops.  More aflatoxins were produced on maize at 35 C than 25 C.  The atoxigenic isolates reduced contamination at both temperatures but the greatest reductions occurred at 25 C.  Results suggest increased production of conidia during host invasion is not associated with increased reductions in contamination during co-infection of hosts.  However, conidia production is likely a key characteristic dictating successful displacement of aflatoxin producers during production of commercial crops. Hosts differentially influenced growth and sporulation of isolates, suggesting isolates have some level of host specialization. Host adaptation may be an important factor influencing compositions of <i>A. flavus</i> populations in agroecosystems and therefore should be taken into consideration when designing biocontrol products.

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