The disease is commonly referred to as root rot or black spot disease and is prevalent in Northeast China, North China, Northwest China, and Zhejiang Province. It can occur at various stages of plant growth. After seedlings emerge, brown lesions appear near the soil surface on young leaves and leaf sheaths. The base and stem gradually become infected, leading to root and stem rot. Affected seedlings are stunted, with an increased number of tillers. Leaves develop oval or spindle-shaped lesions, with a dark brown center, irregular edges, and a lighter surrounding area—hence the term "spot disease." Lesions on the leaf sheaths are larger, elongated, grayish in color, and often have brown spots with indistinct borders. Some spikelets and glumes in the panicle may also turn brown.
The pathogen responsible for this disease is *Cochliobolus sativus* (Ito et Kurib.) Drechsl., which belongs to the Ascomycota phylum. This fungus is a heterothallic species, meaning it requires two compatible mating types to reproduce sexually. It is self-sterile. When cultured on wheat straw extract agar medium with a pH of 6.5, the fungus grows best at 24°C for seven days, then is transferred to 20°C for another 14 days to form conidia. Asexual conidiophores are solitary or grouped in clusters of 2–3, emerging from the host’s epidermis, and are brown with septa. Conidia vary in shape and size, typically cylindrical, straight or slightly curved, with fine ends and a brown color. Their dimensions range from 60–120 μm in length and 15–30 μm in width, with 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 high colonization rates allowing internal hyphae to directly harm seedlings. The pathogen enters through the coleoptile and spreads to young leaves and root caps. Mechanical injuries and insect damage increase susceptibility to infection. Conidiospores produced in infected parts are spread by wind and rain, leading to secondary infections in adult plants, affecting leaves, stems, and ears. Different barley varieties show varying levels of resistance. Continuous cropping, cold injury, poor soil fertility, and insufficient fertilization all contribute to disease development. Maintaining healthy growing conditions and using resistant varieties are essential for effective disease management.
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