Plant Diseases Caused by Fungi

Study Notes

Fungi are eukaryotic, spore-forming, non-chlorophytic organisms, with over 100,000 species, and most are saprophytes.
Around 20,000 species of fungi are parasites and cause disease in crops and plants.
Fungal parasites are the most prevalent plant pathogenic organisms, and individual species can parasitize one or many different kinds of plants.

Fungi are small, eukaryotic, usually filamentous, branched, spore-bearing organisms that lack chlorophyll.
Fungi can be obligate parasites (biotrophs) or non-obligate parasites (facultative saprophytes or facultative parasites).
Fungi have a filamentous vegetative body called a mycelium, which branches out in all directions, with individual branches called hyphae.
Fungi reproduce by means of spores, which are reproductive bodies consisting of one or a few cells.

Fungi have a diverse range of morphological structures, including special root-like structures (rhizoid) for absorbing food.
Parasitic fungi produce special hyphal branches (haustoria) that penetrate host cells and obtain food from the protoplasm.
Some fungi form symbiotic associations with the roots of higher plants (mycorrhizal fungi) or associate with algae (lichens).
Fungi use carbohydrates and nitrogen compounds to synthesize their own amino acids and proteins.

Fungi can cause general or localized signs and symptoms, including general necrosis of host tissue, stunting, distortions, and abnormal changes in plant tissue and organs.
The physical presence of signs of the pathogen (hyphae, mycelia, fruiting bodies, and spores) are significant clues to proper identification and diagnosis of a disease.
Fruiting bodies of fungi range from microscopic to macroscopic and come in many shapes and configurations.

Genetic Host Resistance: Using genetically resistant species, cultivars, varieties, and hybrids.
Cultural Practices:
- Planting only disease-free certified seed.
- Maintaining a balanced fertility program.
- Implementing effective water management.
- Removing crop residues by burning or burying (plowing).
- Implementing crop rotation strategies to reduce or eliminate the interaction of susceptible plants with pathogens.
- Growing crops in climates unsuitable for pathogenic fungi.

Club root of crucifers - caused by Plasmodiophora brassicae
Late blight of potatoes - caused by Phytophora infestans
Pythium seed rot, damping-off, root-rot, and soft rot
Powdery mildews of various crops - caused by many species of fungi of the family Erysiphaceae
Alternaria leafspots - caused by a variety of Alternaria spp.