Aflatoxin in Arizona cottonseed: Field inoculation of bolls byAspergillus flavus spores in wind-driven soil

Conditions typical of an Arizona monsoon were mimicked in the field to inoculate cotton plants withAspergillus flavus. Spores, mixed with autoclaved local soil, were blown onto cotton plants having bolls at all stages of maturity, using a modified commercial leaf blower. Half the plants were sprayed with water following inoculation. After one month, plants were pulled and the position of bolls mapped. All bolls were examined for bright-green-yellow fluorescence (BGYF) of lint, and ginned seeds from each boll were assayed for aflatoxin. Control non-wetted, non-inoculated bolls had no BGYF lint and no aflatoxin-containing seed. In contrast, 15% of the bolls from wetted, inoculated plants exhibited BGYF; 18% of these BGYF bolls had toxin. Only 3% of the non-wetted bolls had BGYF lint and none contained toxin. Lower bolls (fully fluffed at inoculation) were not infected, nor were upper bolls (flower stage at inoculation). Infection occurred only in bolls that had opened during the 30 days following inoculation. While the position of BGYF bolls on naturally contaminated plants was the same as for the inoculated, the ratio of toxic bolls to BGYF bolls was different. All BGYF bolls from plants naturally contaminated withA. flavus contained aflatoxin.