Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2004
Publication Date: 9/1/2004
Citation: Bock, C.H., Mackey, B.E., Cotty, P.J. 2004. Population dynamics of Aspergillus flavus in the air of an intensively cultivated region of South-West Arizona. Plant Pathology. 53:422-433.
Interpretive Summary: The fungus named Aspergillus flavus produces a poison called aflatoxin when it infects cottonseed. Aflatoxin prevents the cottonseed from being used as feed. We have shown that Aspergillus flavus strains which do not produce aflatoxins can effectively prevent contamination by strains which do produce aflatoxins. These strains, called atoxigenic strains, are applied to agricultural fields in order to reduce crop vulnerability to contamination. In the current study, the quantity of Aspergillus flavus in the air was monitored with a special sampler in both a field treated with an atoxigenic strain and a field not treated. The results suggest optimal strategies for utilizing atoxigenic strains of A. flavus to limit aflatoxin contamination. They also show that atoxigenic strain applications can reduce the incidence of aflatoxin producers without increasing the overall quantity of Aspergillus flavus in the air. This suggests atoxigenic strain napplications may improve the safety of the environment as a whole by reducing the incidence of aflatoxin producers, and thus aflatoxins, without increasing the quantity of fungi.
Technical Abstract: Airborne Aspergillus flavus was monitored continuously with two Burkard cyclone samplers from May 1997 to March 1999 at two sites in Arizona surrounded by commercial agriculture. One sampler was initially at the center of 65 ha of cotton treated June 2, 1997 with an atoxigenic vegetative compatibility group (VCG) of A. flavus and the second sampler was about 1 km from the treated field. Propagules in the size range of conidia were collected by the cyclones at levels comparable to those collected by impaction onto 0.8 um pore membranes. Quantities of both total fungi and A. flavus did not differ (P=0.05) between the two sites. Total fungal propagules ranged from 17 to 667 m-3 and from 9 to 1,277 m-3, at the non-treated and treated sites respectively. Counts of A. flavus ranged from <1 to 406 m-3 and <1 to 416 m-3 and A. flavus comprised 1 to 46% and <1 to 51% of the total cultured fungi at the two sites, respectively. Peaks in both total fungal propagules and A. flavus propagules coincided with area-wide boll maturation and cotton harvest. The S strain was most frequent between May and August. The applied VCG was a greater proportion of A. flavus at the treated site than at the non-treated site (P=0.01). Large quantities of A. flavus occurred in the soil (up to 34,474 propagules g-1) of cotton fields and on cotton plant parts and debris (up to 272,461 propagules g-1) adjacent to the cyclone samplers. These data suggest that A. flavus is a major constituent of the air associated with cotton fields in southwest Arizona at certain times of the year. Although application of atoxigenic A. flavus altered the proportion of strains and VCGs in the aerial mycoflora, it did not alter the total quantity of A. flavus.