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Title: Influence of plant host species on intraspecific competition during infection by Aspergillus flavus

item MEHL, HILLARY - University Of Arizona
item COTTY, PETER - US Department Of Agriculture (USDA)

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2012
Publication Date: 2/9/2013
Citation: Mehl, H.L., Cotty, P.J. 2013. Influence of plant host species on intraspecific competition during infection by Aspergillus flavus. Plant Pathology. 2013:1365-3059.

Interpretive Summary: Aflatoxins are carcinogenic toxins produced by fungi in Aspergillus section Flavi that frequently contaminate food and feed crops. The structure of fungal communities influences the incidence and severity of aflatoxin contamination, and an effective management strategy for limiting aflatoxin contamination of crops is to modify the fungal community through competitive exclusion of aflatoxin-producers with atoxigenic biocontrol strains of A. flavus. However, the extent to which the specific crop being infected influences competition between A. flavus individuals has not been studied in detail. In the current study, the ability of paired A. flavus isolates to compete during infection of host tissues and sporulation on host surfaces was compared on sorghum, maize, cottonseed, and soybean. We demonstrated that plant host identity influences outcomes of A. flavus competition. However, outcomes of competition during host tissue invasion did not reflect outcomes of competition during reproduction on all of the hosts. The extent to which diverse A. flavus individuals reproduce on substrates within an agroecosystem determines fungal population structure over time. Thus, results suggest crop hosts have differential influences on A. flavus population structure and the epidemiology of aflatoxin contamination. Furthermore, selection of optimal strains for biocontrol should take into account host-specific influences on the competitive ability of atoxigenic isolates.

Technical Abstract: Communities of Aspergillus flavus are composed of diverse genotypes that collectively influence incidence and severity of crop aflatoxin contamination. Isolates vary in competitive ability on maize, but empirical data on the extent to which host-specific influences determine outcomes of competition are lacking. Seed from maize, cotton, sorghum, and soybean were inoculated individually or in pairs with isolates previously identified as varying in competitive ability on maize kernels. In a separate experiment, the same isolate comparisons were performed on excised cotton locules and Czapek’s agar. Seven days after inoculation, conidia were separated from mycelia imbedded in the substrates, and DNA was isolated separately from each. To quantify outcomes of competition on each of the substrates, isolate-specific single nucleotide polymorphisms were measured using quantitative pyrosequencing. Sporulation varied by host, but within a host treatment, individual isolates did not vary in production of conidia, suggesting isolates do not differ in innate ability to grow on each of the hosts. However, hosts differentially influenced outcomes of competition both during invasion of host tissues and during sporulation on host surfaces, and proportions of isolates from host-infecting mycelia did not predict proportions from conidia. The two most closely related hosts, sorghum and maize, similarly influenced outcomes of A. flavus competition. Competitive interactions in the absence of a host (i.e. Czapek’s agar) did not reflect competition on a host substrate (cotton locules). The current study suggests differential outcomes of competition on various hosts can modify the structure of A. flavus communities and influence the epidemiology of aflatoxin contamination. Crop host influences on A. flavus genotypes and populations should be considered when designing and implementing aflatoxin management strategies.