Rice Blast Disease
Rice blast disease is a recurring issue in China's double-cropping rice regions. It primarily affects the seedlings of late-season rice or the base of stems in mature plants. The infected areas turn brown, and a white, filamentous mycelium appears on the surface. Later, yellow-brown micro-sclerotia form. When late rice seedlings are infected, they may wither and die. Infected plants show yellowing and eventually collapse entirely.
The pathogen responsible for this disease is *Sclerotium rolfsii*, previously known as *S. sclerotiorum*. The sclerotia are spherical to elliptical, ranging from 0.5 to 1 mm in size, and are easily detached. Their surfaces are smooth and shiny, appearing gray or white. Inside, the cells are polygonal and round, measuring about 6–8 micrometers. The outer cells are smaller, irregular, and often brown. The sub-solid layer is dense and white, while the burden is stick-shaped, with 2–4 basal stalks at the top. These structures produce spores that are spherical or pear-shaped, colorless, and measure between 4.5–6.7 μm in length and 3.5–4.5 μm in width.
The sexual stage of the fungus is known as *Corticium centrifugum* (Lv.) Bers., also referred to as *C. rolfii* Curzi (Saccardo). Recently, it has been reclassified as *Athelia rolfsii* (Curzi) Tu and Kimbrough, and is now classified under the Basidiomycetes group. The fungal structure includes basidiospores, which are produced on rod-shaped structures with 2–4 basal stalks. These spores are pear-shaped or oval, transparent, and smooth. In Taiwan, similar behavior has been observed in *Phalaenopsis* orchids.
The disease spreads through the soil during winter, directly infecting the roots, stem bases, or ground-level leaves of nearby plants. In China’s double-cropping rice regions, the main damage occurs when late rice seedlings become infected, leading to significant yield losses.
To manage rice blast disease, farmers typically use methods similar to those for rice rot, including crop rotation, proper drainage, and the application of fungicides. Maintaining good field hygiene and using resistant rice varieties can also help reduce the spread and impact of the disease.
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