Fungal colonization and mycotoxin contamination of developing rice grain

Abstract

Fungal colonization and mycotoxin contamination of developing rice grains of two cultivars (IR-20 and Gowrisanna) were studied during the 1990 and 1991 crop seasons. Field and storage fungi invaded florets while they were still concealed within the boot leaf. Field fungi were most numerous from GS 65 to 77 and then decreased towards GS 91 (fully ripe). Storage fungi also decreased towards harvest. Aflatoxin B₁ was detected at early growth stages but then decreased with decreasing water content. T-2 toxin increased steadily during grain development, and at harvest there was up to 210 ng toxin g⁻¹ grain. Ochratoxin A was not detected until harvest. The incidence of toxigenic A. flavus isolates in fields of the two cultivars differed slightly, but their growth and toxin-producing ability differed greatly between seasons. A. flavus isolates collected during the 1991 crop season produced 26 000 ng aflatoxin B₁ ml⁻¹ medium, much more than was produced by isolates collected during the 1990 crop season.