FUNGAL COLONIZATION AND MYCOTOXIN CONTAMINATION OF DEVELOPING RICE GRAIN

Fungal colonization and mycotoxin contamination of developing rice gra ins of two cultivars (IR-20 and Gowrisanna) were studied during the 19 90 and 1991 crop seasons. Field and storage fungi invaded florets whil e they were still concealed within the boot leaf. Field fungi were mos t numerous from GS 65 to 77 and then decreased towards GS 91 (fully ri pe). Storage fungi also decreased towards harvest. Aflatoxin B1 was de tected at early growth stages but then decreased with decreasing water content. T-2 toxin increased steadily during grain development, and a t 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 an d toxin-producing ability differed greatly between seasons. A. flavus isolates collected during the 1991 crop season produced 26000 ng aflat oxin B1 ml-1 medium, much more than was produced by isolates collected during the 1990 crop season.