Breeding rice for resistance to tungro virus at IRRI

Tungro, one of the most serious diseases of rice, is transmitted by the green leafhopper (Nephotettix virescens) (GLH). The rice tungro spherical virus (RTSV) and rice tungro bacilliform virus (RTBV) cause this disease. Several sources of resistance to RTSV have been identified. However, resistance to RTBV is lacking, although some cultivars such as Buliman Putih, Utri Merah, ARC 11154, and the wild species O. longistaminata and O. rufipogon, have shown tolerance to RTBV. Mass screening in the screenhouse and field screening in hot spots have been used in screening breeding materials. Enzyme linked immunosorbent assay (ELISA) has further allowed the detection of individual virus strains in infected plants. A number of advanced breeding lines developed through backcrossing with elite recurrent rice parents have been evaluated in India, Indonesia, and the Philippines. Promising lines have been identified and some of the agronomically superior lines resistant to tungro have been released as varieties. IR20, IR26, and IR30 were the first tungro resistant cultivars released by IRRI followed by IR28, IR29, IR34, IR36, IR38, and IR40 during the 1970s. Some GLH resistant cultivars such as IR54, IR56, IR60, and IR62 were released in the 1980s followed by PSBRc4, PSBRc10, PSBRc18, and PSBRc28 during the 1990s. Recently, five tungro resistant lines showing resistance to RTSV were released as cultivars in Indonesia and the Philippines. Utri Merah, Balimau Putih, Habiganj DW8, and O. rufipogon served as donors of resistance