Covered smut of barley

Systematic position and nature of the pathogen: Ustilago hordei belongs to the kingdom Fungi, phylum Basidiomycota, class Ustilagiomycetes, and family Ustilaginaceae. It is a specialized phytopathogenic fungus that causes a systemic disease in cereal crops known as covered smut. Unlike loose smut, the spores of this pathogen remain enclosed in a persistent membrane.

Diseases and host plants: The primary host of Ustilago hordei is barley, including both spring and winter varieties. The disease manifests itself during the heading stage. Instead of normal kernels, the ears are replaced by hard, spore-filled masses called sori, which are covered by the host's epidermal layer. These masses remain intact until harvesting, when they eventually break, contaminating healthy seeds.

Biology and life cycle: The infection process occurs exclusively during the germination phase of the seed. Teliospores, carried on the seed coat or present in the soil, germinate alongside the host seed. The hyphae penetrate the seedling tissue and grow systemically within the plant. As the plant approaches the reproductive stage, the mycelium concentrates in the developing ovaries, transforming them into masses of fungal spores.

Conditions for development and spread: The pathogen thrives in soil temperatures ranging from 15°C to 20°C. Moderate soil moisture is essential for the synchronous germination of spores and host seeds, facilitating the successful infection of the coleoptile. Once inside the host, the fungus relies on the plant's metabolic resources to fuel its development until the smut sori are formed.

Economic impact and control measures: The disease causes direct yield reduction as infected plants produce no grain. Effective management is focused on preventing the initial infection:

• Seed treatment with appropriate systemic fungicides is the most effective method of control.
• Utilization of certified, disease-free seed stocks.
• Selection and planting of resistant barley cultivars.
• Proper seed cleaning to remove spore-contaminated debris and dust.