The disease is commonly referred to as root rot or black spot disease. It is prevalent in Northeast China, North China, Northwest China, and Zhejiang Province. The infection can occur at various stages of plant growth. After seedlings emerge, brown lesions appear near the soil surface on young leaves and leaf sheaths. As the disease progresses, the base and stems become infected, leading to root and stem rot. Affected seedlings are stunted, with an increase in tillers. Leaves develop oval or spindle-shaped lesions, typically dark brown in color with irregular edges and a lighter center—hence the name "spot disease." Lesions on the leaf sheaths tend to be larger, elongated, and grayish with brown spots, and their edges are less defined. In some cases, parts of the panicle, such as spikelets and glumes, also turn brown.
The causal agent is *Cochliobolus sativus* (Ito et Kurib.) Drechsl., a member of the Ascomycota phylum. This fungus is a heterothallic species, meaning it requires mating between different strains for sexual reproduction. It is self-sterile. When cultured on wheat straw extract agar medium at pH 6.5, the fungus forms a capsule holder after being incubated at 24°C for seven days and then transferred to 20°C for another 14 days. Asexual conidiophores are solitary or grouped in clusters of two to three, arising from the host’s epidermis, and are brown with septa. Conidia vary in shape and size, usually cylindrical, straight or curved, with fine tips at both ends, and are brown in color. Their dimensions range from 60–120 × 15–30 μm, and they have 3–10 septa. The pathogen exhibits physiological differentiation, with certain races causing severe damage to seedlings, while others affect mature barley plants. It primarily infects barley, wheat, oats, and other grassy weeds.
The transmission of the pathogen occurs through latent infection in seeds or diseased tissues during winter or summer. Seeds serve as the main source of primary infection, with a high colonization rate. Internal hyphae can directly harm the seedlings upon germination. The fungus invades through the coleoptile and spreads to young leaves and root caps. Mechanical injuries and insect damage facilitate pathogen entry. Conidiospores produced in infected tissues are spread by wind and rain, leading to secondary infections in adult plants, affecting leaves, stems, and ears. Resistance varies among varieties, and continuous cropping, along with cold injury, can trigger the disease. Poor soil fertility, inadequate fertilization, and weak plant growth further increase susceptibility.
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