Rice sclerotium stalk rot is primarily caused by *P. ovale* and *P. sclerotiorum*. These two pathogens, either individually or in combination, are also referred to as "sclerotium neck" or "stem rot." They are commonly known as rice brown neck disease, rice blastomycosis, rice gray sclerotia, and are collectively called rice sclerotinia or stem rot. The disease occurs in all rice-growing regions of China, though its prevalence varies by region. In the southern part of the Yangtze River Basin, *Sclerotium rolfsii* and *Sclerotium microsporum* are the main culprits. The symptoms of these two pathogens are similar, affecting the lower leaf sheaths and stems of rice plants.
Initially, small brown spots appear on the leaf sheaths near the water surface. These spots gradually expand into black longitudinal necrotic lines and large black spots. A mold layer containing mycelium often forms within the infected sheath. However, *Sclerotium* species do not form mycelium, and the black lines are shallower. As the lesions continue to spread, the base of the stem turns black and soft, with the affected area appearing grayish or reddish-brown and eventually rotting. The stalks may peel off, and the cavity becomes filled with pale white mycelium and dark brown sclerotia. When the panicle neck is infected, the ear may dry up.
In the case of brown sclerotinia disease, the leaf sheaths yellow and die without forming clear lesions. If the booting ear is affected, the young ears may fail to emerge. Later, spherical black microsclerotia develop in the sheath tissue. For gray sclerotinia, reddish-brown small spots appear on the flag leaf sheath, forming long streaks. This type generally does not cause lodging, but gray-brown granular sclerotia form on the lesion surface and inside over time.
The pathogen *Helminthosporium sigmoideum var. irregulare* (Crall. et Tull.) is now classified as *Nakataea irregulare Hara*, and it belongs to the genus *Aspergillus*. It is a variant of *Escherichia coli* and lacks a sexual stage. Conidial stems are formed on diseased tissue or on the surface of sclerotia, appearing solitary or clustered. The conidia are spindle-shaped, curved, or "S"-shaped, with 3–4 septa, measuring 50–748–12 μm, and have tendril-like filaments on the top cells. Sclerotia are about 0.15 mm in size and have a dark olive color.
Other species include *H. sigmoideum Cav.* = *N. sigmoidea (Cavara) Hara*, which has characteristics similar to *Magnaporthe salvinii Catt. Krause et Webster*, and is known as an *Ascosphere* fungus. It has not yet been found in China. The spore stems are dark brown, unbranched, with crescent-shaped conidia measuring 41–63 × 11–15 μm, with 0–4 septa. Most have more than three septa, with the central two cells dark brown and the ends pale. Sclerotia are spherical, about 0.25 mm in size, with two layers: outer black and inner brown.
*Sclerotium oryzae-sativae Saw* is known as *Sclerotium oryzae-sativae*, with small, round, oval, or cylindrical sclerotia, dark brown, 0.3–2 mm in size, with a rough surface and no distinction between inner and outer layers. *Sclerotium hydrophilum Sacc.* is another species, with spherical, brown to black sclerotia, 0.25–0.68 mm in size, with two layers, and found in leaf sheath tissues, though less commonly.
Several other species, such as *Helicoceras oryzae Linder et Tullis*, belong to *Sclerotium sclerotiorum* and are classified under Deuteromycotina. *Sclerotium murine* is black, 0.14–0.24 × 0.06–0.14 mm, found in leaf sheath tissue. *Sclerotium fumigatum Nak. ex Hara* has spherical to elliptical, gray or gray-brown sclerotia, 0.3–1.5 mm in size, found on the surface of leaf sheaths. *Rhizoctonia solani* (also known as *Sclerotium rhizoctonia oryzae Ryk. et Gooch*) has few, pale red, short column or flat sclerotia, 0.4–1.0 mm in size, found in leaf sheath groups.
Prevention methods include planting resistant varieties such as Zaiguang No. 2, Yongyou No. 4, IR24, Japonica rice 184, Evening No. 6, Liukechun, No. 14, Danhong, Guichao No. 2, Guang Second 104, Shuangfei, Zhenjing 97, Zhenlong 13, Hongmeizao, Agricultural Tiger No. 6, Nonghong 73, Raw Ludiao No. 8, and various indica rice varieties like Xiushui and Xianghu systems. Reducing the bacterial source involves high-temperature composting of diseased straw and cutting it into mud before transplanting. Dry-land rotation can also help. Before transplanting, it’s important to remove sclerotia from the field.
Proper water and fertilizer management is crucial. Keep the field at shallow water levels, and dry it out timely. Avoid early water shortage during the later growth stages. Apply more organic fertilizer and increase phosphorus and potassium, especially potassium, while avoiding excessive nitrogen application. Chemical control includes spraying 40% Difenoxin during the jointing and booting stages, or 40% Fuji No. 1 EC at 1000x, 5% Jinggangmycin at 1000x, 70% Thiophanate-methyl (WP) at 1000x, 50% Ling wettable powder at 800x, 50% Fast Keratin (Pythium) at 1500x, 50% Vincythrin (Nongliling) at 1000–1500x, 50% Isoprenil (Phain) or 40% Sclerotin Net WP at 1000x, and 20% CK Phosphate EC at 1200x.