Plant Diseases Caused by Fungi

Fungal Plant Diseases

• 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.

Biology of Fungi

• 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.

Morphological Characteristics

• 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.

Diagnostic Signs and Symptoms of Fungal Infections

• 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.

Management of Fungal Plant Diseases

• 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.

Examples of Fungal Diseases

• 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.