Wheat snow rot, also known as leaf blight and red snow rot, is a fungal disease that affects wheat from the germination stage through to maturity. It can cause a range of symptoms, including bud rot, seedling drying, sheath rot, leaf drying, ear rot, and leaf blight. Among these, leaf blight and sheath rot are the most significant in terms of impact on crop health.
During the early stages of infection, the radicles, radicle sheaths, and coleoptiles become discolored and rotted, leading to fewer and shorter roots. On the coleoptile, dark brown, bar-shaped or oval spots appear, which may lead to severe rot and the formation of white hyphae on the surface. The base of the leaf sheath turns brown and necrotic, spreading upward and causing the entire leaf to turn brown or yellow and eventually die. Infected seedlings are weak, with underdeveloped or shortened roots, and the first and second leaves are often stunted. In severe cases, the entire plant may be covered in a brownish rot, leading to death and the presence of white mycelium on the surface.
As the disease progresses, the infected parts of the basal pedicels move upward after the jointing stage. The leaf sheaths at the first and second nodes become brown and rotten, turning from dark brown to light yellow over time. Leaves connected to the infected sheaths may also become infected, resulting in rapid browning and wilting. Sheath rot typically starts at the junction between the upper leaf sheath and the leaf blade, spreading toward the base of the leaf blade and lower part of the sheath. The affected sheath becomes yellowish or yellow-brown, with no clear boundary between healthy and diseased tissue. Under high humidity, sparse red mold-like growth may appear.
The upper leaf sheath can lead to the death of the flag leaf and the next leaf. In adult plants, the initial symptoms on the leaves are water-soaked, later forming oval to round spots up to 1–4 cm in size. These lesions are often semi-circular along the leaf margins, with a grayish edge and a brown stain in the center. The infection spreads invasively, creating visible ring-like layers, and brick-red molds are commonly observed on the lesions. When humidity is high, a layer of white hyphae appears around the lesion, and sometimes small black structures—ascospores—are visible.
In the case of spikelets, individual or several spikelets may show black-brown patches on the glumes, accompanied by red mold and brown rot on the rachis. Severe infections can lead to yellowing of the entire ear, with grains becoming wrinkled and brown, and showing a layer of white mycelium on the surface.
The pathogen responsible for this disease is *Gerlachia nivalis* (Ces. ex Sacc.) Gams and Mull., formerly known as *Fusarium nivalis*. It produces conidiophores on infected leaves, forming conidia that are crescent-shaped, colorless, and have 0–3 septa, with most having one. The conidia measure between 11.3–22.8 × 2.3–3.3 μm. The sexual stage is *Monographella nivalis*, producing ascospores that are rod-shaped or cylindrical, measuring 40–70 × 3.5–6.5 μm. Each ascus contains 6–8 ascospores, which are spindle-shaped or elliptical, colorless, and transparent, with 1–3 compartments ranging from 10–18 × 3.6–4.5 μm.
The disease spreads when the pathogen overwinters on seeds, soil, and infected plant debris, then infects leaf sheaths and spreads further, causing repeated infections. The optimal temperature for growth is 19–21°C, with a range from -2°C to 30°C. In regions like the northwest, where April and May bring high rainfall and low temperatures, conditions are favorable for disease development. Similarly, in the Qinghai-Tibet Plateau, July and August bring rain and low temperatures, increasing the risk of infection. The disease not only affects leaves but can also cause ear rot. Wet and cold mountainous areas, as well as irrigation plains, are particularly prone to outbreaks.
Wheat varieties vary in their resistance to the disease, and planting dates, water and fertilizer management, and sowing density all play a role in disease development. Excessive spring irrigation, late nitrogen application, and high humidity can increase the likelihood of infection. Sowing too early or using excessive seeding rates can also contribute to disease spread.
To manage the disease, it is recommended to use resistant varieties such as Zhengzhou No. 3, Huapei 28, Xiaojing No. 6, Zhoumai No. 10, Abo, Xinong 88, Xinong 881, Fengchan No. 3, and Qinmai No. 12. Ensuring the use of disease-free seeds is essential. Timely sowing, proper plant density, and balanced fertilization are important practices. In areas with high humidity and dense planting, applying fungicides such as 80% carbendazim ultrafine powder (1000 times dilution), 36% thiophanate suspension (500 times), 50% benomyl WP (1500 times), or 25% triadimefon EC (2000 times) before and after winter can help control the disease effectively.
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