Sensitivity of Fusarium moniliforme Isolates to Pefurazoate

Abstract

From the infected rice seeds with “Bakanae” disease collected in various districts in Japan, 518 isolates of Fusarium moniliforme were isolated and examined for their sensitivity to pefurazoate, an inhibitor of an ergosterol biosynthesis. The minimum inhibitory concentration (MIC) values of the compound were in a range from 0.78ppm to 12.5ppm, and the less sensitive isolates, which were reported for triflumizole known as an ergosterol biosynthesis inhibitor (EBI), to pefurazoate were not observed. However, both the fungicides had a similar trend in the sensitivity pattern of F. moniliforme, so that the isolates less sensitive to triflumizole were also low sensitive to pefurazoate (MIC: 6.25ppm to 12.5ppm). On the base of the different sensitivity to those EBIs and benomyl, the isolates could be classified into four types; isolates sensitive to both of the EBIs and benomyl (I), isolates sensitive to EBIs and resistant against benomyl (II), isolates moderately sensitive to the EBIs and sensitive to benomyl (III) and isolates moderately sensitive to the EBIs and resistant against benomyl (IV). The ratios of the isolates I, II, III and IV were 8.5%, 83.0%, 8.1% and 0.4%, respectively. The ability of these isolates to produce gibberellins and fusaric acid was estimated. The isolates I, II and IV produced gibberellins, but the isolate III did not produce them. Fusaric acid was produced by all the types of isolates, and there was no clear difference in the sensitivity to the fungicides. Rice seeds artificially inoculated with the isolate IV were disinfected with pefurazoate which showed similarly high effect as in the seeds inoculated with the isolate I, indicating that the difference in sensitivity in vitro was irrelevant to the actual effect of seed treatment.