Cereal production plays a major role in both animal and human diets throughout the world. However, cereal crops are vulnerable to attacks by fungal pathogens on the foliage, disrupting their biological cycle and photosynthesis, which can reduce yields by 15–20% or even 60%. Consumers are concerned about the excessive use of synthetic pesticides given their harmful effects on human health and the environment. As a result, the search for alternative solutions to protect crops has attracted the interest of scientists around the world. Among these solutions, biological control using beneficial microorganisms has taken on considerable importance, and several biological control agents (BCAs) have been studied, including species belonging to the genera Bacillus, Pseudomonas, Streptomyces, Trichoderma, Cladosporium, and Epicoccum, most of which include plants of growth-promoting rhizobacteria (PGPRs). Bacillus has proved to be a broad-spectrum agent against these leaf cereal diseases. Interaction between plant and beneficial agents occurs as direct mycoparasitism or hyperparasitism by a mixed pathway via the secretion of lytic enzymes, growth enzymes, and antibiotics, or by an indirect interaction involving competition for nutrients or space and the induction of host resistance (systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathway). We mainly demonstrate the role of BCAs in the defense against fungal diseases of cereal leaves. To enhance a solution-based crop protection approach, it is also important to understand the mechanism of action of BCAs/molecules/plants. Research in the field of preventing cereal diseases is still ongoing.

Penicillium expansum causes blue mold, a major post-harvest disease affecting apples. This disease is commonly managed using fungicides, including Difenoconazole (Dif), a demethylation inhibitor (DMI) approved for its control. This investigation aims to evaluate the baseline sensitivity of 100 P. expansum isolates to Difenoconazole. The isolates were collected from symptomatic apples in 34 storage warehouses across the Fes-Meknes and Draa-Tafilalet regions over three years (2020, 2021, and 2022). The study revealed an increase in the percentage of inhibition of mycelial growth and spore germination of P. expansum proportional to the increasing concentration of the fungicide. Moreover, the results indicate that 46 isolates were able to develop even at a concentration of 5 µg/mL of Dif (the suggested discriminatory dose), indicating reduced sensitivity to this fungicide. The analysis of the values of the effective concentration to inhibit 50% (EC50) of mycelial growth of P. expansum ranging from 0.027 to 1.673 µg/mL (mean: 0.263 µg/mL, variation factor: 62.507) and for spore germination from 0.0002 to 0.787 µg/mL (mean: 0.048 µg/mL, variation factor: 4113.835). The wide variation in EC50 values indicates significant variability in the isolates’ responses to Dif, likely due to diverse sampling in space and time. Our results showed that some P. expansum isolates could grow even at high concentrations of Dif, indicating limited efficacy of this treatment. The EC50 of five isolates exceeded 0.92 µg/mL, suggesting potential resistance. This study indicates reduced sensitivity and possible emergence of resistant strains. Notably, it is the first evaluation of P. expansum sensitivity to Dif in Morocco.

The apple tree (Malus domestica), a member of the Rosaceae family, holds significant economic value but faces postharvest challenges, like blue mold caused by Penicillium expansum and gray mold caused by Botrytis cinerea. While synthetic fungicides are widely used, their limitations highlight the need for sustainable alternatives. This study explores the antifungal properties of extracts from Celtis australis, Olea europea var. sylvestris, Chamaerops humilis, and Asparagus albus against these pathogens. In vitro tests assessed mycelial growth inhibition, whereas in vivo trials consisted of measurement of weight loss, firmness, total soluble solids, titratable acidity, and maturity index. Moreover, the phytochemical traits of the extracts were determined using the Folin–Ciocalteu method and HPLC. The results revealed notable antifungal activity, particularly for Celtis australis extract at a concentration of 300 g L⁻¹, which led to significant mycelial growth inhibition (61% for P. expansum and 41% for B. cinerea), a reduction in diseases’ severity (39% and 50%), and a notable decrease in diseases’ incidence (43% and 48%), respectively. Phytochemical analysis reflected the presence of phenols and flavonoids in the tested extracts. Importantly, the natural treatments helped preserve the apples’ quality during storage. Molecular docking studies further revealed that major compounds in Celtis australis extract inhibit the 14α-demethylase enzyme, a key target in fungal sterols biosynthesis.