Interaction of Fluorescent Pseudomonads with Pythium ultimum and Rhizoctonia solani in Cucumber Roots

The effects of the fluorescent pseudomonad isolate CW2 on hyphae of Pythium ultimum (Trow) and Rhizoctonia solani (Kühn) and root colonization were studied in gnotobiotic systems under scanning electron microscopy (SEM). Results of SEM revealed that the frequency of bacterial colonization was higher in cucumber roots infested with the fungi than in healthy roots. Isolate CW2 caused irregular and abnormal fungal growth. Swellings and shrinkages of P. ultimum and R. Solani hyphae were obvious when cucumber roots were drenched with CW2. SEM studies were also conducted to evaluate the effect of CW2 on hyphae of both fungi on PDA medium. The hyphae of P. ultimum and R. solani showed distinct morphological alterations and degradation compared to untreated healthy control hyphae of Pythium or Rhizoctonia which were slender and uniform in shape. The results provide direct evidence of bacterial attachment and colonization to fungal hyphae of both tested spp. and show that fungal growth to be significantly reduced in the presence of isolate CW2