Effects of the biocontrol agent Pseudomonas fJuofescens Q2·87 that is
known to produce the antibiotic 2.4-diacetylphloroglucinol (2.4-DAPG) on
phytopathogenic Pythium spp, In relation to electron microscopic analysis of t~e
hyphal cen walls were Investigated, The outcome of the antagonistic Interactlcos
between this strain and Pythium spp .. by means of light and scanning electron
microscope, when co-cultivated on potato dextrose agar was described. Lig~t
micrographs are presented that displayed hyphal distortion. swollen shapes and
unusual apical branching. In addition, scanning electron micrographs are also
presented that dIsplayed degradation of the cell wall layers and revealed the cellulosic
wall microfibrillar skeleton. A similar cell wall degradation was observed when POt
medium was emended with the synthetic antibiotic 2,4·DAPGflhus. It might b~
concluded that the natural antibiotic 2,4-DAPG i!t primarily respo~ib\e for antagonistic
process of the Oomycete P. ultimum induced by P. fJuorescens 02·87. Our results
based on ultrastructural observations provide evidence that the modes of this strair1
action in Inhibition. preventing colonization by Pythium are mainly associated with
major cell wall degradation, and eventually death of Pythium cells, as a result of
extensive celf wall breakdown.