Innate Vulnerability of Oryza glaberrima to Rice tungro bacilliform virus

Rice tungro disease (RTD) is a serious threat to rice production in South and Southeast Asia. RTD is caused by Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). Coinfection of RTSV and RTBV results in more severe symptoms in African rice Oryza glaberrima than in Asian rice O. sativa. In this study, we examined whether RTBV alone causes more severe symptoms in O. glaberrima than in O. sativa. The examination of 18 accessions of O. glaberrima for RTBV infection indicated that all the O. glaberrima accessions examined were susceptible to RTBV. The reactions to RTBV of three O. glaberrima accessions and two RTBV-susceptible varieties of O. sativa, Taichung Native 1 (TNI) and IR 64, were compared. RTBV accumulation varied depending on the plants and differences in RTBV accumulation were not evident between the two species. However, the O. glaberrima accessions were significantly more stunted by RTBV than IR 64 was. Discoloration of leaves by RTBV was evident in the O. glaberrima plants, but not in the O. sativa plants. Collectively, these results presumably indicated that O. glaberrima is generally more vulnerable to RTBV than O. sativa is.