LACK OF A ROLE FOR FLUORESCENT SIDEROPHORE PRODUCTION IN THE BIOLOGICAL-CONTROL OF PYTHIUM DAMPING-OFF OF CUCUMBER BY A STRAIN OF PSEUDOMONAS-PUTIDA

Hyphal growth but not sporangial germination of Pythium ultimum was inhibited by the synthetic iron chelating compound ethylenediamine (di-o-hydroxyphenylacetic acid) (EDDHA) on water agar and by strain N1R of Pseudomonas putida on King's medium B. Eight prototrophic derivatives of N1R (deficient in fluorescent siderophore [pyoverdine] biosynthesis [Pvd-]) were obtained by Tn5 mutagenesis. Pvd- derivatives did not inhibit hyphal growth of P. ultimum on King's medium B, but protected cucumber seedlings from Pythium damping-off in three different agriculture soils at levels statistically indistinguishable from the parental strain, N1R. Therefore, pyoverdine production by strain N1R was not critical to biocontrol of Pythium damping-off of cucumber under the conditions of this study.