|GARBER, N - University Of Arizona|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2013
Publication Date: 5/1/2014
Citation: Garber, N.P., Cotty, P.J. 2014. Aspergillus parasiticus communities associated with sugarcane in the Rio Grande Valley of Texas: implications of global transport and host association within Aspergillus section flavi. Phytopathology. 104:462-471.
Interpretive Summary: Aflatoxin contamination of corn and cottonseed is a serious problem in the Rio Grande Valley of Texas (RGV). Diverse communities of aflatoxigenic fungi have been associated with contamination events in this region. Crop rotation apparently influences both the fungi present and the average aflatoxin producing potential of the resident fungal communities. Aflatoxin producing fungi cultured from soils previously cropped to sugarcane are morphologically distinct from section Flavi isolates dominant in RGV soils with no history of sugarcane. The sugarcane associated isolates resemble Aspergillus parasiticus in colony and spore morphology and in production of both aflatoxins B1 and G1. Similar isolates have previously been reported from sugarcane fields in Japan. Incidence of unusual isolates increased over the first four years of sugarcane production and rapidly declined after rotation out of cane. DNA sequence and vegetative compatibility tests were used to characterize relationships among sugarcane-derived isolates from Japan and RGV and A. parasiticus. The results suggest that aflatoxin-producing isolates have been transported around the world in association with sugarcane billets and maintained in different geographic areas under sugarcane cultivation.
Technical Abstract: In the Rio Grande Valley of Texas (RGV) values of maize and cottonseed crops are significantly reduced by aflatoxin contamination. Aflatoxin contamination of susceptible crops is the product of communities of aflatoxin producers and the average aflatoxin-producing potentials of these communities influence aflatoxin contamination risk. Cropping pattern influences community composition and thereby the epidemiology of aflatoxin contamination. In 2004, Aspergillus parasiticus was isolated from two fields previously cropped to sugarcane but not from 23 fields without recent history of sugarcane cultivation. In 2004 and 2005, A. parasiticus composed 18 to 36% of Aspergillus section Flavi resident in agricultural soils within sugarcane producing counties. A. parasiticus was not detected in counties that do not produce sugarcane. Aspergillus section Flavi soil communities within sugarcane producing counties differed significantly dependent on sugarcane cropping history. Fields cropped to sugarcane within the previous five years had greater quantities of A. parasiticus (mean = 16 CFU/g) than fields not cropped to sugarcane (mean = 0.1 CFU/g). The percentage of Aspergillus section Flavi composed of A. parasiticus increased to 65% under continuous sugarcane cultivation, and remained high the first season of rotation out of sugarcane. Section Flavi communities in fields rotated to non-sugarcane crops for three to five years were composed of <5% A. parasiticus, and fields with no sugarcane history averaged only 0.2% A. parasiticus. The section Flavi community infecting RGV sugarcane stems ranged from 95% A. parasiticus in billets prepared for commercial planting, to 52% A. parasiticus in hand-collected sugarcane stems. Vegetative compatibility assays and multilocus phylogenies verified that aflatoxin contamination of raw sugar was previously attributed to similar A. parasiticus in Japan. Association of closely related A. parasiticus genotypes with sugarcane produced in Japan and RGV, frequent infection of billets by these genotypes, and the ephemeral nature of A. parasiticus in RGV soils suggests global transport with sugarcane planting material.