Molecular Mechanisms of Fungal Pathogenicity in Apple Canker

Apple canker, principally caused by Valsa mali and related Cytospora species, represents a major threat to pome fruit production worldwide. At the heart of this disease lies a complex interplay of fungal virulence factors and host defence responses. The pathogen secretes a battery of cell‐wall‐degrading enzymes, notably xylanases and cellulases, which breach host cell walls and liberate nutrients. Concurrently, an array of small toxic metabolites and effector proteins suppress host programmed cell death and disrupt redox homeostasis. On the plant side, innate immunity is orchestrated by membrane‐bound pattern-recognition receptors and intracellular nucleotide-binding leucine-rich repeat proteins that perceive pathogen-derived signals and activate defence gene networks. Hormonal pathways centred on jasmonic acid and ethylene, as well as chromatin remodelling via histone deacetylases, further modulate transcriptional responses. Recent advances have also revealed the role of microRNA and microRNA-like RNAs in fine-tuning gene expression during infection. Together, these molecular insights are guiding the development of early-detection assays, resistant cultivars and targeted biocontrol strategies.

Research from Nature Portfolio

Advances in quantitative molecular diagnostics have uncovered latent reservoirs of V. mali in crabapple and apple seeds, seedlings and twigs. A highly sensitive real-time PCR assay, employing species-specific primers, revealed that a significant proportion of apparently healthy seeds and nursery stock harbour fungal DNA. This latent infection can intensify during seedling development and persist in nursery twigs, identifying novel inoculum sources. The study underscores the need for improved sanitation and screening of planting material to curb orchard epidemics.

Molecular Mechanisms of Fungal Pathogenicity in Apple Canker publication trend

The graph below shows the total number of articles in molecular mechanisms of fungal pathogenicity in apple canker across all publications each year (not limited to Nature Index journals).

Technical terms

Nucleotide-binding leucine-rich repeat (NLR) protein: An intracellular immune receptor that recognises pathogen-derived molecules and activates defence responses.

Effector protein: A secreted fungal molecule that manipulates host cellular processes to promote infection.

MicroRNA-like RNA (milRNA): Small regulatory RNA produced by fungi that can modulate expression of both fungal and host genes.

Histone deacetylase: An enzyme that removes acetyl groups from histones, leading to chromatin condensation and changes in gene expression.

Xylanase: A cell-wall-degrading enzyme that breaks down xylan polymers, facilitating pathogen ingress and nutrient acquisition.

References

1. Adaptive regulation of miRNAs/milRNAs in tissue-specific interaction between apple and Valsa mali. Horticulture Research (2024).
2. MdVQ12 confers resistance to Valsa mali by regulating MdHDA19 expression in apple. Molecular Plant Pathology (2023).
3. Xylanase VmXyl2 is involved in the pathogenicity of Valsa mali by regulating xylanase activity and inducing cell necrosis. Frontiers in Plant Science (2024).
4. Latent Infection of Valsa mali in the Seeds, Seedlings and Twigs of Crabapple and Apple Trees is a Potential Inoculum Source of Valsa Canker. Scientific Reports (2019).
5. Candidate effector proteins of the necrotrophic apple canker pathogen Valsa mali can suppress BAX-induced PCD. Frontiers in Plant Science (2015).
6. Toxins Produced by Valsa mali var. mali and Their Relationship with Pathogenicity. Toxins (2014).
7. Valsa mali Pathogenic Effector VmPxE1 Contributes to Full Virulence and Interacts With the Host Peroxidase MdAPX1 as a Potential Target. Frontiers in Microbiology (2018).
8. Apple Valsa canker: insights into pathogenesis and disease control. Phytopathology Research (2023).