INFLUENCE OF FIELD APPLICATION OF AN ATOXIGENIC STRAIN OF ASPERGILLUS-FLAVUS ON THE POPULATIONS OF ASPERGILLUS-FLAVUS INFECTING COTTON BOLLS AND ON THE AFLATOXIN CONTENT OF COTTONSEED

An atoxigenic strain of Aspergillus flavus was applied to soils plante d with cotton in Yuma, Arizona, to assess the ability of the atoxigeni c strain to competitively exclude aflatoxin-producing strains during c otton bell infection and thereby prevent anatoxin contamination of cot tonseed. In both 1989 and 1990, the atoxigenic strain displaced other infecting strains during cotton boil development. Displacement was ass ociated with significant reductions in the quantity of aflatoxins cont aminating the crop at maturity. Although frequency of infected locules differed between years (1% versus 25%), in both years displacement oc curred without increases in the amount of infection as measured by the quantity of locules with bright-green-yellow-fluorescence (BGYF). In the law infection year(1990), locules exhibiting BGYF were analyzed in dividually for both incidence of the applied strain and anatoxin conte nt. In the high infection year (1989), infected seed from each replica te plot (32 total) were pooled and analyzed for both anatoxin and inci dence of the released strain. Results of the latter analyses indicate an inverse relationship (r = 0.71, P < 0.001) between anatoxin content and the percent seed infected by the applied strain. In 1990, quantit ies of A. flavus on mature crop surfaces did not differ between treate d and untreated plots. When reisolated from the infected crop the appl ied atoxigenic strain retained the atoxigenic phenotype. Most infectin g strains belonging to other vegetative compatibility groups did produ ce detectable quantities of anatoxin BI in liquid fermentation. The ap plied atoxigenic strain spread from treated plots to untreated control s at different rates in the two years and accounted for 7 and 25% of A . flavus strains isolated from infected locules in untreated control p lots in 1990 and 1989, respectively. The results suggest that the anat oxin-producing potential of A. flavus populations associated with crop production can be reduced in order to reduce anatoxin contamination.