Resistance to Seven Site-Specific Fungicides in Botrytis cinerea from Greenhouse-Grown Ornamentals

Inhibitory and Curative Effects and Mode of Action of Hydroxychloroquine on Botrytis cinerea of Tomato

Gray mold is an important disease of crops and is widespread, harmful, difficult to control, and prone to developing fungicide resistance. Screening new fungicides is an important step in controlling this disease. Hydroxychloroquine is an anti-inflammatory and antimalarial agent that has shown marked inhibitory activity against many fungi in medicine. This study evaluated the inhibitory activity of hydroxychloroquine against several phytopathogenic fungi, finding a half-maximal effective concentration of 113.82 μg/ml against the hyphal growth of Botrytis cinerea, with significant in vivo curative effects of 92.37 or 78.37% for gray mold on detached tomato leaves or fruits at 10.0 or 200.0 mg/ml, respectively. Ultrastructural studies indicated that hydroxychloroquine induced collapse of hyphae, with a wrinkled surface, unclear organelle boundaries, and organelle disintegration. Transcriptomic assays revealed that hydroxychloroquine could affect the expression of metabolism-related genes. Molecular docking and molecular dynamics analyses indicated that hydroxychloroquine bound to glucose-methanol-choline oxidoreductase, with a low free energy value of -11.4 kcal/mol. Cell membrane permeability assays and hyphal staining confirmed that hydroxychloroquine damaged the cell membrane, causing leakage of hyphal contents and disturbing cell function. Biochemical assays indicated that hydroxychloroquine reduced the concentration of soluble proteins and reducing sugars in the hyphae. Overall, hydroxychloroquine disturbed amino acid metabolism, therefore inhibiting the production of biomacromolecules, damaging the cell membrane, and restraining the growth of hyphae, hence inhibiting gray mold on tomato. This study explored the use of medicine in the development of agricultural fungicides and their application in managing crop diseases, providing valuable background information.

Biocontrol Efficacy of Pseudomonas Consortia Against Botrytis Blight in Petunias

Botrytis cinerea, a fungal pathogen causing Botrytis blight, significantly impacts greenhouse crop management owing to its broad host range and infection capabilities at various growth stages. Traditional control methods, primarily reliant on fungicides, are challenged by environmental concerns and the rise of fungicide-resistant strains. This study investigates the use of beneficial Pseudomonas bacteria as a sustainable alternative. We hypothesized that specific Pseudomonas consortia could provide more effective biocontrol of B. cinerea than individual strains. Our research investigated five Pseudomonas strains (14B11, AP54, 15H3, 94G2, and 89F1) known to reduce Botrytis blight in Petunia × hybrida. Compatibility for bacterial consortia was assessed through biofilm formation and direct bacterial inhibition assays. The biocontrol effects of the bacteria against B. cinerea were investigated in vitro using shared-air-space and dual-culture assays and in planta by inoculating detached petunia flowers. We found that strain 14B11 exhibited the highest biofilm formation, with consortia of 14B11 and 89F1 showing significant enhancement compared with individual cultures, whereas a slight, nonsignificant increase was observed in 14B11 and AP54 consortia. However, strain 14B11 efficacy was inhibited by strain 15H3. Genomic analyses identified antifungal compound-related gene clusters in 14B11 and AP54, contributing to their biocontrol potential. Trials with detached flowers of Petunia × hybrida 'Carpet Red Bright' confirmed significant disease severity reduction with 14B11, AP54, and their consortia. This research highlights strategic Pseudomonas consortia as promising, eco-friendly alternatives to chemical fungicides, promoting sustainable agriculture by enhancing our understanding of how microbial interactions can be used to manage Botrytis blight.

Carboxylesterase and Cytochrome P450 Confer Metabolic Resistance Simultaneously to Azoxystrobin and Some Other Fungicides in Botrytis cinerea

Plant pathogens have frequently shown multidrug resistance (MDR) in the field, often linked to efflux and sometimes metabolism of fungicides. To investigate the potential role of metabolic resistance in B. cinerea strains showing MDR, the azoxystrobin-sensitive strain B05.10 and -resistant strain Bc242 were treated with azoxystrobin. The degradation half-life of azoxystrobin in Bc242 (9.63 days) was shorter than that in B05.10 (28.88 days). Azoxystrobin acid, identified as a metabolite, exhibited significantly lower inhibition rates on colony and conidia (9.34 and 11.98%, respectively) than azoxystrobin. Bc242 exhibited higher expression levels of 34 cytochrome P450s (P450s) and 11 carboxylesterase genes (CarEs) compared to B05.10 according to RNA-seq analysis. The expression of P450 genes Bcin_02g01260 and Bcin_12g06380, along with the CarEs Bcin_12g06360 in Saccharomyces cerevisiae, resulted in reduced sensitivity to various fungicides, including azoxystrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin, iprodione, and carbendazim. Thus, the mechanism of B. cinerea MDR is linked to metabolism mediated by the CarE and P450 genes.