Biocontrol Activity of Actinomycetes Strains against Fungal and Bacterial Pathogens of Solanum lycopersicum L. and Daucus carota L.: In Vitro and In Planta Antagonistic Activity

Abstract

Plants are affected by various biotic and abiotic stresses due to climate change. Tomato and carrots are important crops that are attacked by various pathogens. Fourteen plant-growth-promoting bacteria (PGPB) belonging to the genera Streptomyces sp. and Nocardiopsis sp. were selected for the biocontrol of several common fungal and bacterial pathogens. Antifungal activity was assessed against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Rhizoctonia solani (RHS). Antibacterial activity was evaluated against Pseudomonas syringae (PS), Pseudomonas corrugata (PC), Pseudomonas syringae pv. actinidiae (PSA), and Pectobacterium carotovorum subsp. Carotovorum (PCC). In vitro antifungal and antibacterial antagonistic activities were evaluated by the dual culture method. Fungal–bacterial interaction areas were analyzed by scanning electron microscopy (SEM). Cell-free culture filtrates (CFs) from strains showing good biocontrol potential were produced and investigated for their in vitro antifungal and antibacterial activity. The two most effective strains were also combined in consortium and utilized for In Planta pre-emergence biocontrol assays on both S. lycopersicum and D. carota. For each pathogenic strain, four experimental conditions were compared: CNT (no PGPB/no infection), PGPB (with PGPB/no infection), PGPB+INF (with PGPB/with infection), and INF (no PGPB/with infection). Streptomyces albidoflavus strain H12 and Nocardiopsis aegyptica strain H14 showed good in vitro antifungal (inhibition of >50%) and antibacterial (inhibition halo of >10 mm) activity. The SEM micrographs showed deterioration of fungal filaments and modification of hyphal structures. The CFs of both strains were also able to inhibit FORL and RHS in in vitro growth (minimum inhibitory concentration of 0.2–0.8%). In planta biocontrol assessments showed that the consortium was effective in reducing the infection effects of both fungal and bacterial pathogens. Dual consortium allowed regular plant development compared to the control. These results confirm the usefulness of actinomycetes strains as a biocontrol agent and can therefore be an alternative to chemicals used in agriculture.

Evaluating the Antagonistic Potential of Actinomycete Strains Isolated From Sudan’s Soils Against Phytophthora infestans

“…Nevertheless, different clades within the Streptomyces genus could be identified, which grouped strains that also shared some phenotypic features such as melanoid pigment production or induction of specific phenotypes in mycelial growth of P. infestans (Figures 1, 3). In view of their prolific synthesis of specialized metabolites, Actinomycetes have been repeatedly described to inhibit the growth and development of various plant pathogenic organisms (Abdallah et al, 2013;Chen et al, 2016;Djebaili et al, 2021). Among the many pathogens threatening plant growth and health, the oomycete P. infestans is one of the most important ones (Kamoun et al, 2015).…”

“…In view of their prolific synthesis of specialized metabolites, Actinomycetes have been repeatedly described to inhibit the growth and development of various plant pathogenic organisms ( Abdallah et al, 2013 ; Chen et al, 2016 ; Djebaili et al, 2021 ). Among the many pathogens threatening plant growth and health, the oomycete P. infestans is one of the most important ones ( Kamoun et al, 2015 ).…”

“…Although few examples of plant pathogenic Actinomycetes exist, such as Streptomyces scabies causing common scab of potato ( Keinath and Loria, 1989 ), many more Actinomycetes have been reported to inhibit the development of a broad range of phytopathogenic fungi ( Berg et al, 2001 ). Among these, different species of Streptomyces and Nocardiopsis showed activity in vitro and in planta against fungal and bacterial pathogens of tomato and carrot ( Djebaili et al, 2021 ), while Streptomyces coelicolor was reported to be very potent at controlling onion bacterial rot and at reducing the disease incidence throughout onions’ storage time ( Abdallah et al, 2013 ). Furthermore, Chen et al (2016) showed that both cells and culture filtrate of Streptomyces plicatus inhibited mycelial growth and zoospore germination of the pepper pathogen Phytophthora capsici .…”

The Potential Use of Actinomycetes as Microbial Inoculants and Biopesticides in Agriculture

“…S. albidoflavus H12 and Nocardiopsis aegyptica H14 inhibit the growth of several bacterial phytopathogens, such as Pseudomonas syringae, P. corrugata, and Pectobacterium carotovorum subsp. carotovorum (203). S. ramulosus, S. axinellae, and S. drozdowiczii produce a crude extract active against Ralstonia solanacearum, the causal agent of bacterial wilt (204).…”

Marine Actinomycetes, New Sources of Biotechnological Products

“…The bioactive compounds produced by these actinomycete species are used by the plants for protection, and the bacteria that produce these protective bioactive compounds are known as plant growth promoting bacteria (PGPB). Many of these PGPB are Streptomyces species that possess both antifungal and antibacterial properties [ 234 ]. Though much of the current research on plant–PGPB symbioses in actinomycetes has focused on terrestrial environments, marine actinomycetes may also display similar growth-promoting properties.…”