Research in plant pathology has increasingly focused on developing environmentally friendly, effective strategies for controlling plant diseases. Cyanobacteria, including Desmonostoc muscorum, Anabaena oryzae, and Arthrospiraplatensis, were applied to Capsicum annuum L. to induce immunity against Fusarium wilt. Soil irrigation and foliar shoots (FS) application were used in this investigation. The disease symptoms, disease index, osmotic contents, total phenol, Malondialdehyde (MDA), hydrogen peroxide (H₂O₂), antioxidant enzymes (activity and isozymes), endogenous hormone content, and response to stimulation of defense resistance in infected plants were assessed. Results demonstrated that using all cyanobacterial aqueous extracts significantly reduced the risk of infection with Fusarium oxysporum. One of the most effective ways to combat the disease was through foliar spraying with Arthrospira platensis, Desmonostoc muscorum, and Anabaena oryzae (which provided 95, 90, and 69% protection percent, respectively). All metabolic resistance indices increased significantly following the application of the cyanobacterial aqueous extracts. Growth, metabolic characteristics, and phenols increased due to the application of cyanobacteria. Polyphenol oxidase (PPO) and peroxidase (POD) expressions improved in response to cyanobacteria application. Furthermore, treatment by cyanobacteria enhanced salicylic acid (SA) and Indole-3-Acetic Acid (IAA) in the infected plants while decreasing Abscisic acid (ABA). The infected pepper plant recovered from Fusarium wilt because cyanobacterial extract contained many biologically active compounds. The application of cyanobacteria through foliar spraying seems to be an effective approach to relieve the toxic influences of F. oxysporum on infected pepper plants as green and alternative therapeutic nutrients of chemical fungicides.

In this study, the decolorization efficiency of seven microalgae isolates; Nostoc muscorum, Nostoc humifusum, Spirulina platensis, Anabaena oryzae, Wollea saccata, Oscillatoria sp. and Chlorella vulgaris was investigated for dye decolorization. The highest decolorization percentages of Brazilwood, Orange G, and Naphthol Green B dyes (99.5%, 99.5%, and 98.5%, respectively) were achieved by Chlorella vulgaris. However, the maximum efficiency for dye decolorization percentages of CV and malachite green dyes were exhibited by A. oryzae (97.4%) and W. saccata (93.3%). Ligninolytic enzymes activity assay was carried out for laccase and lignin peroxidase enzymes, which revealed a high efficiency of the C. vulgaris, A. oryzae and W. saccata to lignin containing compound degradation. The highest laccase production recorded by C. vulgaris with Brazilwood, Orange G, and Naphthol Green B dyes (665.0, 678.6, and 659.5 U/ml, respectively). Similarly, C. vulgaris gave a high lignin peroxidase enzyme production with the above three dyes respectively (306.00, 298.34, and 311.45 U/ml). In addition, A. oryzae and W. saccata showed the highest production of the laccase enzyme (634.6 and 577.45 U/ml, respectively) with CV and malachite green dyes. The degradation products have been characterized after decolorization and verified using FTIR analysis. The high decolorization percentages achieved by C. vulgaris, A. oryzae and W. saccata make them potential candidates for bioremediation and pre-processing to remove dyes from textile effluents.

Microalgae and cyanobacteria are rich sources of numerous phytochemical compounds with intrinsic antifungal potential. This research aimed to screen the phytochemical compounds and contents, as well as the antioxidant profiles, in eight cyanobacterial and two microalgal strains isolated from soil and brackish water habitats in Egypt. Our study also evaluated their antifungal activities against three phytopathogenic fungi—namely, Pythium ultimum, Fusarium solani, and Botryodiplodia theobromae, which are known to cause severe plant loss. The biochemical compounds were obtained from the cyanobacterial and algal methanolic extracts, and were identified through comparative phytochemical analyses related to the inhibition of the fungal pathogens. Comparative qualitative analyses of alkaloids, steroids, glycosides, and saponins were also carried out. The quantitative phytochemical screening of the cyanobacterial and algal strains investigated revealed the presence of xylanase, glucanase, and chitinase enzymes, along with some bioactive compounds, such as phenolics, flavonoids, proteins, neutral sugars, and carotenoids, which were species-dependent and detected in variable amounts in the extracts. The unicellular green microalgal strain Dunaliella sp. HSSASE13 displayed the highest level of antioxidant activity. However, the highest antifungal activities were shown by the heterocystous cyanobacterial strain Anabaena sp. HSSASE11 (83.94%), followed by Dunaliella sp. HSSASE13 (81.94%) and the non-heterocystous cyanobacterial strain Oscillatoria nigro-viridis HSSASE 15 (63.42%), against the three fungal pathogens B. theobromae, F. solani, and P. ultimum, respectively. Our results indicate that the highest significant and positive correlations of flavonoids (r = 0.854), phenolics (r = 0.785), DPPH scavenging activity (r = 0.876), total proteins (r = 0.808), xylanase activity (r = 0.876), glucanase activity (r = 0.746), and total neutral sugars (r = 0.764), in terms of their antifungal activities, were recorded against F. solani. Conclusively, the cyanobacterial and algal strains tested in the present study can be useful agents for the management and biocontrol of plant-infecting fungal pathogens.

Salinity adversely affects the plant’s morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.