Assessment of resistance to rice tungro disease in popular ricevarieties in India by introgression of a transgene against Rice tungrobacilliform virus

AbstractRice crops in South and Southeast Asian countries suffer critical yield losses due to rice tungro disease caused by jointinfection with rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). Previously, for generating RNAinterference-based transgenic resistance against tungro viruses, RTBV ORF IV was used as a transgene to develop RTBVresistance in a popular high-yielding scented rice variety. The transgene from this line was then introgressed into five popularhigh-yielding but tungro-susceptible rice varieties by marker-assisted backcross breeding with a view to combine theresistant trait with the agronomic traits. The present work includes a resistance assay of the BC3F5lines of these varietiesunder glasshouse conditions. Out of a total of 28 lines tested, each consisting of 12 individual plants, eight lines showedsignificant amelioration in height reduction and 100- to 1000-fold reduction in RTBV titers. The RNAi-mediated resistancewas clearly manifested by the presence of virus-derived small RNA (vsRNA) specific for RTBV ORF IV in the transgenicbackcrossed lines