Screening of soil bacteria with antagonistic activity against Pythium ultimum, a major plant pathogen oomycete

BELTRAMINO MURIEL; GRBICH MARIANA; LANDONI SOFÍA; VULETIC EZEQUIEL; LUJAN ADELA; ALBARRACIN ORIO A

Los Cocos

Congreso; XVIII Congreso Argentino de Microbiolgía General; 2022

Sociedad Argentina de Microbiología General

Oomycetes, from the kingdom Stramenopila, include numerous destructive pathogens in genera such as Pythium and Phytophthora. The genus Pythium consists of approximately 120 species that can be found in diverse niches from terrestrial ecosystems to salt water estuaries. Many species are plant pathogens while others are strict soil saprophytes. P. ultimum is the causal agent of the damping-off, one of the main diseases of agriculture crops of economic importance such as cotton. The control of the disease is carried out mainly through the application of chemical products both to the seeds and to the crop, or through the use of resistant cultivars. However, the growing concern for environmental care translates into the use of more sustainable agricultural alternatives such as biological control practices. Plant growth promoting bacteria have been studied both for their ability to directly promote the crop and to inhibit the development of a wide variety of pathogens. The objective of this work was to isolate P. ultimum controlling bacteria from different soil samples. We collected soil samples from different locations of Córdoba, with and without cotton cultivation. Soil bacteria were recovered by shaking the samples in sterilized saline solution for 20 min and plating soil suspensions serially diluted on different agar media and incubated at 28ºC for 2 days. The activity of all the isolates against P. ultimum was screened by co-cultures on Potato Dextrose Agar (PDA) plates. Antagonism was evaluated by measuring the radial growth of the pathogen after 2-4 days of incubation at 28ºC. An average of 2.5 x108 CFU/g of soil was obtained for each sample and from total recovered bacteria 150 isolates were selected to evaluate their activity against the oomycete. No controlling ability was observed for strains belonging to genus Bacillus, whereas a small group of Pseudomonas or Pseudomonas-like isolates were able to inhibit P. ultimum. The great majority of the antagonistic isolates found belonged to the phylum Actinobacteria. These strains, which vary in general macroscopic aspect, strongly inhibit the growth of P. ultimum (47.8 to 92.0%). Moreover, actinobacterial isolates were able to provoke macroscopic alterations in the mycelium of the oomycete, which showed less density of its aerial structure. These are promising results that reveal the usefulness of actinobacterial strains as biocontrol agents of one of the most problematic soil plant pathogen and can therefore be an alternative to chemicals used in agriculture. The next steps in this line of research will focus on the characterization of these isolates and their bioactive metabolites.