Biocontrol of Soil-Borne Pathogens of Solanum lycopersicum L. and Daucuscarota L. by Plant Growth-Promoting Actinomycetes: In Vitro and In Planta Antagonistic Activity.

Claudia Ercole,Mahmoud Kitouni,Marika Pellegrini,Maddalena Del Gallo,Rihab Djebaili,Beatrice Farda

doi:10.3390/pathogens10101305

Claudia Ercole, Mahmoud Kitouni + Show 4 more

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https://doi.org/10.3390/pathogens10101305

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Abstract

Biotic stress caused by pathogenic microorganisms leads to damage in crops. Tomato and carrot are among the most important vegetables cultivated worldwide. These plants are attacked by several pathogens, affecting their growth and productivity. Fourteen plant growth-promoting actinomycetes (PGPA) were screened for their in vitro biocontrol activity against Solanum lycopersicum and Daucus carota microbial phytopathogens. Their antifungal activity was evaluated against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Rhizoctonia solani (RHS). Antibacterial activity was evaluated against Pseudomonas syringae, Pseudomonas corrugata, Pseudomonas syringae pv. actinidiae, and Pectobacterium carotovorum subsp. carotovorum. Strains that showed good in vitro results were further investigated in vitro (cell-free supernatants activity, scanning electron microscope observations of fungal inhibition). The consortium of the most active PGPA was then utilized as biocontrol agents in planta experiments on S. lycopersicum and D. carota. The Streptomyces albidoflavus H12 and Nocardiopsis aegyptica H14 strains showed the best in vitro biocontrol activities. The diffusible and volatile compounds and cell-free supernatants of these strains showed both antifungal (in vitro inhibition up to 85%, hyphal desegregation and fungicidal properties) and antibacterial activity (in vitro inhibition >25 mm and bactericidal properties). Their consortium was also able to counteract the infection symptoms of microbial phytopathogens during in planta experiments, improving plant status. The results obtained highlight the efficacy of the selected actinomycetes strains as biocontrol agents of S. lycopersicum and D. carota.

Highlights

Tomato (Solanum lycopersicum L.) and carrot (Daucus carota L.) are among the most important vegetables of the Solanaceae and Apiaceae families [1,2]
The in vitro biocontrol activity against pathogenic bacteria was evaluated by dual culture, investigating the activity of diffusible compounds
The in vitro assays and in planta experiments highlighted the suitability of the consortium formed by Streptomyces albidoflavus H12 and Nocardiopsis aegyptica H14 as a biocontrol agent

Summary

Introduction

Tomato (Solanum lycopersicum L.) and carrot (Daucus carota L.) are among the most important vegetables of the Solanaceae and Apiaceae families [1,2] These plants are attacked by several soil-borne pathogens that induce severe diseases, which affect plant productivity. Through beneficial microorganism enlistment via root exudates, counteract the attacks of soil-borne pathogens [9,10] Among these microorganisms, known as plant growth-promoting bacteria (PGPB), actinomycetes are an important source of bioactive and antimicrobial metabolites and control a wide range of phytopathogens [11]. We screened the biocontrol capabilities of fourteen Streptomyces spp. and Nocardiopsis spp. actinomycetes that have already been demonstrated to be used as biostimulants [15] and salt stress-tolerance agents [16] Given these capabilities, we hypothesized that these strains could be valid biocontrol agents against fungal and bacterial pathogens. We evaluated the efficacy of in planta biocontrol in tomato and carrot plants in greenhouse experiments

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