Resistance to sulfonylurea herbicides, including bensulfuron-methyl, pyrazosulfuron-ethyl, imazosulfuron and ethoxysulfuron, was discovered in naturally occurring populations of Lindernia micrantha D. Don in rice ®elds that had been treated with sulfonylurea-based herbicides for 3±7 consecutive years. The resistant biotype was approximately 80»300 times more resistant than the susceptible one to the above four sulfonylurea herbicides. This is the second con®rmed occurrence of herbicide resistance resulting from the use of sulfonylurea herbicides in Japan. Several herbicides with dierent modes of action, including pretilachlor, cafenstrole, bifenox, naproanilide, thiobencarb + simetryn + MCPB, MCPA-thioethyl + simetryn and cyhalofop-butyl + bentazone, eectively controlled the resistant biotype in pot trials.

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An isosurface c an be eciently generated by visiting adjacent intersected c ells in order, as if the isosurface were p r opagating itself. We previously proposed an extrema graph method, which generates a graph connecting extremum points. The isosurface p r opagation starts from some of the intersected c ells that are found both by visiting the cells through which arcs of the graph pass and by visiting the cells on the boundary of a volume.In this paper, we propose an ecient method o f searching for cells intersected by an isosurface. This method generates a volumetric skeleton consisting of cells, like an extrema graph, by applying a thinning algorithm used in the image recognition area. Since i t preserves the topological features of the volume and the connectivity of the extremum points, it necessarily intersects every isosurface. The method is more ecient than the extrema graph method, since i t d o es not require that cells on the boundary be visited.