Bioprospecting Fluorescent Pseudomonas from the Brazilian Amazon for the Biocontrol of Signal Grass Foliar Blight

Abstract

Biological control is considered the only viable integrated disease management practice for controlling the widely distributed and destructive foliar blight and sudden death disease caused by the fungus Rhizoctonia solani AG-1 IA on signal grass (Urochloa brizantha) pastures. Since major signal grass varieties are highly susceptible and fungicide sprays are not labeled for grass pasture cropping systems, biological control is sought as an alternative for managing this fungal disease. In this study, 24 fluorescent Pseudomonas isolates obtained from naturally suppressive soils from the Amazon biome were bio-prospected for their role as biocontrol agents against R. solani AG-1 IA. Based on in vitro antagonism, three isolates (Amana, Poti, and Yara) were selected for further in vivo assays. Multilocus phylogenetic analysis indicated that Amana and Yara were grouped into the Pseudomonas putida group while Poti was grouped into the Pseudomonas asplenii group, and could well constitute a new Pseudomonas species. For in vivo biocontrol assays, the biocontrol agents were applied either via seed-treatment or via foliar spray. All three isolates produced siderophores and solubilized phosphate, while Amana and Poti showed protease and chitinase in vitro activity. Foliar application of P. putida Amana from Amazonian suppressive soils resulted in a significant reduction of the foliar blight disease severity on signal grass. We discuss further steps for the development and labeling of Pseudomonas-based biofungicides for managing the foliar blight disease on signal grass pastures in Brazil.

BIOLOGICAL CONTROL OF Corynespora cassicola AND Drechslera tritici-repentis

“…The control of phytopathogenic fungi using bacteria of the genus Pseudomonas (Rodriguez and Pfender, 1997, Yang et al, 2014, Vicentini et al, 2022, Pantoea (Dutkiewicz et al, 2016), and Bacillus (Ferraz et al, 2008, Bach et al, 2016 has been reported in the scientific literature. According to Asaturova et al (2022), when using B. velezensis against D. tritici-repentis, a reduction in the mycelial growth of pathogens of up to 94.3% was observed at 15 days in in vitro tests.…”

“…promoting growth, assisting in obtaining nutrients, and promoting the induction of resistance to diseases and pests by activating metabolic pathways of plant physiology (Dutkiewicz et al, 2016). These characteristics are also present by some species of the genus Bacillus (Bach et al, 2016) and Pseudomonas (Vicentini et al, 2022).…”

“…According to Vicentini et al (2022), the direct inhibitory effect is given by the release of antifungal substances, such as protease, chitinase, and phosphatase that will act on the mycelia, causing the inhibition of their growth and/or development, in addition to causing injuries to the already formed cells. Another bacterial strategy to impair the mycelial growth of the pathogen is the production of a biofilm.…”

“…The formulation of commercial biofungicides has gained a substantial market (Meyer et al, 2016, Meyer et al, 2019, Agrofit, 2022. Its use in vivo can bring, in addition to controlling severity and incidence, other benefits for plant growth and yield (Bach et al, 2016, Dutkiewicz et al, 2016, Larran et al, 2016, Asaturova et al, 2022, Vicentini et al, 2022. Future studies are needed with these bacteria in formulations for in vivo tests to compare their social, environmental, economic, and agronomic impact, having as reference the chemical control of these pathogens.…”

“…Using microorganisms considered biocontrollers may be an option in the range of possibilities for disease management. Traditionally, the genera Pseudomonas, Bacillus, and Pantoea have been considered effective in managing some phytopathogenic fungi in various regions of the world (Ludwig and Moura, 2007;Correa et al, 2010;Dutkiewicz et al, 2016;Vicentini et al, 2022). Several species of these genera have demonstrated the ability to produce antibiotics, mechanisms of competition for resources with the pathogen, or induction of plant resistance (Dutkiewicz et al, 2016;Dimkić et al, 2022).…”