The most important rice disease in the southern United States (Groth and Lee, 2003) and the second most important in the world (Ou, 1985) is sheath blight, caused by Rhizoctonia solani Kühn AG1-1A [teleomorph: Thanatephorus cucumeris (A.B. Frank) Donk.] ( Rush and Lee, 1992). Under conditions favourable for disease development, rice grain yield losses, ranging from 4% to 50%, have been attributed to sheath blight ( Lee and Rush, 1983; Marchetti, 1983; Marchetti and Bollich, 1991).