Nature of "pecky rice" on parboiled rice in Rio Grande do Sul, Brazil

Abstract

This research was conducted under laboratory conditions at the Faculdade de Agronomia da UFRGS, in Porto Alegre, RS, Brazil, from 1985 to 1987, with the main purpose of elucidating the nature of "pecky rice" on parboiled rice. Clean rice grains, cultivar BR-IRGA 409, were sterilized with methyl bromide, and the samples were inoculated with one of the following fungi: Aspergillus flavus, Curvularia lunata, Fusarium moniliforme and Helminthosporium oryzae. Inoculated samples and the control were submitted (or not) to a simulated parboiling process. The largest number of discolored rice grains was shown by the samples inoculated with Curvularia lunata, and such discoloration was much more pronounced on the endosperm and on the embryo than on the glumes. In Helminthosporium oryzae - inoculated samples, the largest numbers of discolored grains were found on those of intact grains and on the parboiled dehulled grains, what may be an indication that the parboiling process increases the discoloration. The total number of discolored grains decreased in the following order: samples with C. lunata, with H. oryzae, with F. monilliforme, with A. flavus, and non-inoculated samples.