Classification of Plant Pathogens

Study Notes

Classification of Plant Pathogens

Fungal pathogens are categorized into three main types: biotrophs, necrotrophs, and hemibiotrophs, with additional distinctions of 6 monocotrophs and 11 phylogenetic classifications.
Global strategies to combat plant pathogens include biosecurity, agronomy, genetic methods, and chemical treatments, with optimization in genetic and chemical approaches emphasized.

Phenotypic Classification of Plant Diseases

Symptoms can classify plant diseases:
- Pathogen-related symptoms (rust, mildew, smut)
- Host symptoms (blotch, spot, dieback)
Host-specific classifications include wheat and barley rust.
Color-based classification includes yellow rust and brown rust.

Classification by Culturability

Pathogens can be categorized based on culturing:
- Obligate pathogens require living plants to grow, while facultative pathogens can grow on dead organic matter.
Culturability may not reflect feeding methods in the plant host.

Trophic Classifications

Saprotrophs feed on dead organic matter; biotrophs consume living plant cells, while necrotrophs feed on dying or dead cells.
Biotrophs cause symptoms reflective of the pathogen, whereas necrotrophs produce symptoms related to the host's response.

Hemibiotrophy Definition

Hemibiotrophy exhibits both biotrophic and necrotrophic phases, identified by temporal and spatial differentiation in pathogenic interactions, notably in species like Colletotrichum and Magnaporthe grisea.

Evaluation of Trophic Trisomy

Biotrophy classification tends to capture many pathogens but leaves questions for intermediaries.
Noted pathogens include Cladosporium fulvum and Phytophthora infestans, displaying specific feeding mechanisms like haustoria for nutrient extraction.

Limitations of Trophic Trisomy

Viruses are classified separately due to their intracellular nature, while bacteria are known for wilting and vascular blockage.

Factors Influencing Biotrophs

Require living host cells and are obligate in nature, with haustoria for nutrient uptake.
Typically exhibit a narrow host range and utilize salicylic acid in defense mechanisms.
Engage in gene-for-gene interactions involving virulent effectors.

Characteristics of Hemibiotrophs

Start off feeding on living cells, transitioning to dead tissue, and are facultative.
Possess haustorium-like structures; narrow host range; utilize both salicylic and jasmonic acid in defense.
Feature avirulent effectors and qualitative resistance genes.

Key Traits of Necrotrophs

Feed on dead or dying cells; facultative with no haustoria.
Broad host range, utilizing jasmonic acid in defense, and possessing specific toxins and necrotrophic effectors.
Resistance genes can exhibit quantitative traits.

Role of Effectors

Effectors are pathogen-produced molecules influencing host interactions;
Loss of virulence factors in biotrophs leads to pathogenicity confirmation.
Necrotrophs deploy host-specific toxins to facilitate infection, while hemibiotrophs often possess virulence effectors, revealing complexity in pathogen-host interactions.

Shift in Pathogen Classification

With advancements in genomic studies, traditional trophic classifications are being reevaluated, leading to a more nuanced understanding of pathogen categories.

Description

Explore the classification of various fungal pathogens and their definitions. Learn about different strategies for combating plant diseases on a global scale, including biosecurity and agronomy. This quiz covers key concepts related to plant pathology and disease management.