Antagonistic activity of rizosphere bacteria against soil inhabiting fungal pathogens of small grain cereal crops

Ivo Yanashkov, Tzenko Vatchev

Abstract: Root and lower stem disease complex causing seedling blight before or after emergence of the seedlings, root and lower stem rot in older plants is among the most economically important diseases affecting small grain cereal crops. The causal agents include various soil inhabiting, pathogenic fungi and fungal-like oomycetes. Along with detrimental pathogens, various plant-beneficial symbiotic microorganisms are found in rhizosphere of cereal plants including bacteria of genus Pseudomonas, Rhizobium, Bacillus etc. Through their extracellular metabolic activity these can antagonize wide range of soil inhabiting plant pathogens and thus have potential to be effective biological control agents. In the present study in vitro laboratory experiments were conducted to evaluate potential antagonistic activity of single rhizosphere isolates belonging to five bacterial species, namely Pseudomonas marginalis, Rhizobium radiobacter, Bacillus casei, B. subtilis and B. pumilus, against seven major cereal-crops soilborne pathogens. The isolates of B. subtilis and P. marginalis showed broad antagonistic activity inhibiting mycelial growth of six different plant pathogens, as follows: Fusarium culmorum – by 22.6% and 16.7%, Fusarium graminearum – by 33.3% and 24.3%, Fusarium oxysporum – by 30.7% and 29.0%, Fusarium sporotrichiella – by 34.8% and 36.8%, and Fusarium equiseti – by 35.4% and 32.7%, respectively. The isolates of B. subtilis and P. marginalis showed antagonistic activity to Drechslera sorokiniana and Pythium ultimum, respectively, reducing mycelial growth of both pathogens by 41.6%. The B. pumilus isolate antagonized the same pathogen species as B. subtilis but generally to a lower extent. B. casei demonstrates antagonistic activity against four fungal pathogens including F. culmorum, F. graminearum, F. oxysporum and F. equiseti, revealing 11.8%, 22.8%, 29.5% and 9.6% inhibition of mycelial growth, respecyively, but shows some stimulating effect (6.9%) to F. sporotrichiella. Among the tested candidate bioagents R. radiobacter exhibited no or weak antagonistic activity against the pathogens.

Keywords: antagonistic activity; bioagents; rhizobacteria; small grain cereal crops; soilborne fungal pathogens

Date published: 2018-05-23