Aflatoxin-Producing Fungi Associated With Sugarcane: Host Relations, Persistence in the Environment, and Relationships within Aspergillus Section Flavi

Abstract

Aflatoxin is a carcinogenic mycotoxin. Aflatoxin contamination of susceptible crops is the product of communities of Aspergillus section Flavi and average aflatoxin-producing potential of these communities influence aflatoxin contamination risk. In 2004 and 2005, Sugarcane producing counties in the Rio Grande Valley of Texas (RGV) had unique aflatoxin-producing communities containing Aspergillus parasiticus. Sugarcane fields or those rotated for less than two years had Aspergillus section Flavi communities dominated by A. parasiticus. A. parasiticus was rarely detected in long-term rotation fields and not detected in counties without sugarcane crops. Aflatoxin-producing fungi infecting RGV sugarcane stems ranged from 52 - 95% A. parasiticus in hand-collected samples and billets for commercial planting, respectively. Identical A. parasiticus fungi found in Japan caused aflatoxin contamination of raw sugar there. Population genetics and phylogenetics were used to characterize a global sampling of 112 A. parasiticus and identify geographic distributions and crop associations within the species. One population shows clear association with sugarcane and is distributed to Asia, Africa and North America, implicating human involvement in its distribution. A. parasiticus populations from maize and peanut have broad geographic distribution but crop specific lineages and/or populations were not detected. One A. parasiticus population isolated from maize has a distribution limited to Mexico. A phylogeny generated from a partial nitrate reductase gene resolves a lineage that correlates with the sugarcane population and suggests crop association and geographic distribution may drive divergence within A. parasiticus. Crop associations shape fungal communities and must be considered for aflatoxin management. Native food enthusiasts in Arizona conduct public millings of wild- and landscape-collected mesquite pods (Prosopis spp.) to produce mesquite flour, which is often consumed in the same localities where it is produced without conventional food safety inspection. Aflatoxin was found in imported, domestic, and non-commercial mesquite flour batches, with 10% above the FDA action level for human food (>20 ppb), and 95% could not be exported to Europe (>2 ppb). Aflatoxin content in Tucson was largely explained (63%) by harvest date with those harvested later yielding more aflatoxin. Lateral flow aflatoxin assay of mesquite flour proved viable for lab and public testing.