1. Pre-infection Defense Mechanisms:
a. Physical barriers: The outermost layer of plant cells, called the cuticle, acts as a physical barrier that prevents the entry of fungal spores or hyphae into the plant tissues.
b. Antimicrobial substances: Certain horticultural crops produce antimicrobial substances such as phytoalexins, which are synthesized in response to pathogen infection and have antifungal properties.
c. Trichomes: Some plants develop trichomes, which are hair-like structures on the leaf surface that can trap and entangle fungal spores, preventing their germination.
2. Post-infection Defense Mechanisms:
a. Hypersensitive response: Upon successful penetration by a fungal pathogen, some plants undergo a localized hypersensitive response. This response involves rapid cell death in the infected area, effectively isolating the pathogen and preventing further spread of the infection.
b. Systemic acquired resistance (SAR): Once a plant has been infected by a pathogen, it can develop enhanced resistance to subsequent infections by the same or related pathogens. This phenomenon, known as SAR, involves the production of chemical signals that travel throughout the plant, priming its defense systems.
c. Induced systemic resistance (ISR): Certain beneficial microbes, such as plant growth-promoting rhizobacteria (PGPR), can trigger ISR in plants. ISR enhances the plant's overall defense capabilities against various pathogens.
d. Pathogenesis-related (PR) proteins: In response to infection, horticultural crops produce a range of PR proteins. These proteins have diverse functions, such as inhibiting fungal growth, degrading fungal cell walls, and activating defense-related signaling pathways.
e. RNA interference (RNAi): Some plants employ RNAi to target and degrade specific fungal transcripts, interfering with the pathogen's gene expression and reducing its virulence.
It is important to note that the effectiveness of these defense mechanisms can vary among different horticultural crop species and may also be influenced by environmental factors and the specific fungal pathogen encountered.
