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Natural Occurrence of Fumonisins in Rice with Fusarium Sheath Rot Disease

Twenty samples of rough rice (Oryza sativa) (unpolished kernels) collected during the 1995 harvest season from Arkansas (seven samples) and Texas (13 samples) were obtained from rice fields known to include plants with symptoms of Fusarium sheath rot putatively caused by Fusarium proliferatum. Samples were analyzed for fumonisin B₁ (FB₁) at three laboratories using three different extracting solvents by high-performance liquid chromatography (HPLC) or enzyme-linked immunosorbent assay (ELISA) methods. Forty percent of the samples were positive for FB₁ at levels ≤4.3 μg/g by HPLC. The same samples contained FB₁ at ≤3.6 μg/g when measured by an ELISA method. Most samples that were positive for FB1 were positive for fumonisin B₂ (FB₂) and fumonisin B₃ (FB₃) by HPLC at levels ≤1.2 μg/g. Very good agreement was obtained among the two laboratories using HPLC methods and the third using ELISA. Shelling of the unpolished rice results in hull and brown rice fractions. In a sample that contained 4.3 μg/g in whole kernels, the fumonisin level was very high in hulls (≤16.8 μg/g) and low in brown rice (≤0.9 μg/g). Milling of brown rice results in bran and white rice fractions. Fumonisins were found in bran at a level of ≤3.7 μg/g but were below the level of detection by HPLC in white rice. The presence of fumonisins (FB₁, FB₂, and FB₃) was confirmed by fast atom bombardment/mass spectrometry. This is the first report of fumonisins in naturally contaminated rice in the United States.