1999 Volume 65 Issue 2 Pages 153-162
Alcaligenes faecalis No.4 (No.4), which showed a significant suppressive effect on the growth of 13 kinds of plant pathogens in vitro, produced hydroxylamine, nitrite and nitrate in liquid cultivation. This indicates that No.4 is a heterotrophic nitrifier. As hydroxylamine solution formed a clear growth inhibitory zone on a plate inoculated with Rhizoctonia solani K-1 in vitro, the aforementioned suppressive effect was considered to be due to the hydroxylamine produced by No.4 during heterotrophic nitrification. When culture broth, cell suspension and supernatant of No.4 were applied to sterilized soil containing R. solani, the damping-off of tomato seedlings caused by R. solani was suppressed significantly. However, in non-sterilized soil, damping-off was suppressed only by the culture broth and the cell suspension treatments, presumably because hydroxylamine in the supernatant was decomposed in soil. Transposon mutagenesis was applied to No.4 to produce a non-hydroxylamine-producing mutant, No.4-1, which showed no suppressive effect on the growth of R. solani either in vitro or in vivo. These data indicate that the hydroxylamine produced by No.4 is involved in the suppression of damping-off caused by R. solani.
