Plant growth-promoting bacteria (PGPB) afford plants several advantages (i.e., improvement of nutrient acquisition, growth, and development; induction of abiotic and biotic stress tolerance). Numerous PGPB strains have been isolated and studied over the years. However, only a few of them are available on the market, mainly due to the failed bacterial survival within the formulations and after application inside agroecosystems. PGPB strains with these challenging limitations can be used for the formulation of cell-free supernatants (CFSs), broth cultures processed through several mechanical and physical processes for cell removal. In the scientific literature there are diverse reviews and updates on PGPB in agriculture. However, no review deals with CFSs and the CFS metabolites obtainable by PGPB. The main objective of this review is to provide useful information for future research on CFSs as biostimulant and biocontrol agents in sustainable agriculture. Studies on CFS agricultural applications, both for biostimulant and biocontrol applications, have been reviewed, presenting limitations and advantages. Among the 109 articles selected and examined, the Bacillus genus seems to be the most promising due to the numerous articles that support its biostimulant and biocontrol potentialities. The present review underlines that research about this topic needs to be encouraged; evidence so far obtained has demonstrated that PGPB could be a valid source of secondary metabolites useful in sustainable agriculture.

Twenty species of the Laboulbeniales parasitic on beetles (Coleoptera) are reported for the first time from Ecuador.

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.

No abstract

Intensive agricultural practices have led to intense soil degradation and soil fertility losses. Many soil-borne diseases affect these intensive agricultural soils, worsening the physical-chemical and fertility imbalances. Among the numerous pathogens, the genus Fusarium includes members that destroy many crops, including Crocus sativus L., which also impairs the composition and functions of the microbial communities. This work aimed to investigate, for the first time, the bacterial communities of the rhizosphere of saffron in the presence and absence of fusariosis. The rhizosphere of the saffron fields in the territory of L’Aquila (Italy) with and without fusariosis was sampled and subjected to a microbiological analysis. Culture-dependent methods characterized the fusariosis. The dehydrogenase activity assay was estimated. The metabarcoding of the 16S rRNA gene, a metagenome functioning prediction, and a network analysis were also carried out. The results showed that fusariosis, when it is linked to intensive agricultural practices, causes alterations in the microbial communities of the rhizosphere. The culture-dependent and independent approaches have shown changes in the bacterial community in the presence of fusariosis, with functional and enzymatic imbalances. The samples showed a prevalence of uncultured and unknown taxa. Most of the known Amplicon Sequence Variants (ASVs) were associated with the Pseudomonadoa (syn. Proteobacteria) lineage. The composition and richness of this phylum were significantly altered by the presence of Fusarium. Moreover, pathogenesis appeared to improve the ASVs interconnections. The metagenome functions were also modified in the presence of fusariosis.