Aggregate sheath spot and sheath spot of rice

Aggregate sheath spot and sheath spot of rice are caused by Rhizoctonia oryzae-sativae (Sawada) Mordue and R. oryzae Ryker & Gooch, respectively. Although sheath spot is usually considered as a minor disease, it can be a very aggressive disease of rice. Aggregate sheath spot was also regarded as minor until the disease became increasingly important in temperate rice-growing regions such as California and south eastern Australia. The potential yield loss caused by both diseases was unknown until recent research clearly demonstrated the potential threat aggregate sheath spot and sheath spot represent to temperate rice industries. Worldwide, aggregate sheath spot and sheath spot have received little attention compared with the disease sheath blight, caused by Rhizoctonia solani. This article reviews the information available on both R. oryzae-sativae and R. oryzae relating to distribution, host range, biology, symptoms, disease cycle, epidemiology, pathogenicity, identification and control methods, yield losses and resistance. This paper is the first comprehensive review of sheath spot and aggregate sheath spot of rice.