Question

Plant disease caused by fungi
- classification of plant pathogenic fungi

Answer 1

Plant pathogenic fungi are classified based on various criteria including their life cycle, morphology, and the type of symptoms they produce on host plants. A common classification divides them into several categories, including:

### 1. **Based on Taxonomic Classification:**
- **Ascomycetes (Sac Fungi):**
- E.g., *Fusarium*, *Botrytis*, *Monilinia*
- **Basidiomycetes (Club Fungi):**
- E.g., *Ustilago* (smuts), *Puccinia* (rusts)
- **Zygomycetes:**
- E.g., *Rhizopus*, *Mucor*
- **Chytridiomycetes:**
- E.g., *Allomyces* (less common in plants but still notable)
- **Deuteromycetes (Imperfect Fungi):**
This group comprises fungi that do not have a known sexual reproduction stage.
- E.g., *Colletotrichum*, *Cercospora*, *Phytophthora* (though often classified with Oomycetes)

### 2. **Based on the Nature of Infection:**
- **Biotrophic Fungi:**
- These fungi require living host tissues to complete their life cycle. They do not kill the host quickly and may cause chronic disease.
- E.g., *Puccinia* spp. (rust fungi)
- **Necrotrophic Fungi:**
- These fungi kill host tissues and feed on the decaying organic matter.
- E.g., *Botrytis* spp., *Sclerotinia* spp.
- **Hemibiotrophic Fungi:**
- These fungi have a life cycle that includes both a biotrophic phase and a necrotrophic phase.
- E.g., *Colletotrichum* and *Fusarium* spp.

### 3. **Based on Symptomatology:**
- **Leaf Spot Fungi:**
- E.g., *Cercospora*, *Alternaria*
- **Root Rot Fungi:**
- E.g., *Pythium*, *Rhizoctonia*
- **Blight and Wilts:**
- E.g., *Botrytis cinerea* for blights, *Fusarium* for wilts.
- **Rusts and Smuts:**
- E.g., *Puccinia* spp. (rusts), *Ustilago* spp. (smuts)

### 4. **Based on Host Specificity:**
- **Monophagous:**
- Fungi that infect only one species or closely related species.
- **Oligophagous:**
- Fungi that infect a few species or closely related species.
- **Polyphagous:**
- Fungi with a broad host range, infecting many different plant species.

### 5. **By Mode of Spore Production:**
- **Sexual Reproduction:**
- Fungi that produce sexual spores (ascospores or basidiospores).
- E.g., *Aspergillus nidulans* (Ascomycete)
- **Asexual Reproduction:**
- Fungi that produce asexual spores (conidia, sporangiospores).
- E.g., *Aureobasidium pullulans* (Deuteromycete)

### Conclusion
The classification of plant pathogenic fungi is complex and can overlap in various systems. Understanding these classifications is essential for plant disease management, allowing for more targeted strategies to control and mitigate the impact of plant diseases caused by fungi.