Abstract
Some characteristics of Gibberella fujikuroi (Fusarium moniliforme) isolates less-sensitive to triflumizole which inhibit an ergosterol biosynthesis were studied with special reference to the pathogenicity and the production of gibberellins. Out of 500 isolates from naturally infected rice seeds and seedlings, the MIC values of 433 isolates (86.6%) were 10ppm and below, whereas 30 isolates (6.0%) were 1, 000ppm or more but the EC50 values were less than 1.3ppm and there was a little difference between the least sensitive and the most sensitive ones, thus being classified less-sensitive. Fungal properties of less-sensitive isolates were similar to those of sensitive ones. Inoculating rice seeds and flowers with the conidial suspension of sensitive isolates caused high incidences of “Bakanae” disease, which with less-sensitive ones rarely occurred. Rice seedling test showed that gibberellin-like substances produced by sensitive isolates in Richard's medium were greater than those by less-sensitive ones, estimation by HPLC also indicating that sensitive isolates produced over three times more GA3 than less-sensitive ones. There was, however, no clear difference in fusaric acid production between sensitive and less-sensitive isolates. The lower production of gibberellins by less-sensitive isolates coincided with being less in the pathogenicity.
