The Differential Reaction of Rice Hybrids to Tungro Virus by Phenotyping and PCR Analysis

AbstractTwenty popular rice hybrids were used to screen for rice tungro virus(RTV) disease reaction. Virulent green leafhoppers (GLH) were used asvector to introduce RTV to the rice hybrids. Virus symptoms scores wererecorded at 14, 21, 34, 41 and 59 days postinoculation (DPI), which sug-gested that virus symptoms are greatly influenced by growth stage ofplants. To confirm the presence of virus, polymerase chain reaction(PCR)-based detection of Rice tungro bacilliform virus (RTBV) was carriedout at 7, 14, 21 and 59 DPI using virus genome-specific primers. Viruspresence was observed in all the rice hybrids and check varieties, particu-larly at later stages of infection. This study shows that phenotyping fortungro virus resistance in rice hybrids at 21 DPI gives most reliable resultsbased on both virus symptoms and presence of virus. Further, to assessthe relative difference in population of RTBV, quantitative PCR was per-formed in all the genotypes at 21 DPI. Yield data were also recorded fromcontrol and virus-infected plants to estimate yield loss percentage due totungro disease. This study is important to understand the response of ricehybrids to tungro virus disease. Results obtained in this study emphasizethat molecular detection of virus is very important to screen the riceplants accurately for tungro disease reaction.IntroductionRice is the staple food for more than half of theworld’s population. In India, it is considered as themost important food crop and holds the key of foodsecurity. To meet the challenges imposed by growingpopulation and decreasing farm resources, rice pro-ductivity has been enhanced with the deployment ofsemi-dwarf high-yielding varieties. Further increasein rice productivity can be obtained through hybridrice technology. The capability of hybrid rice to meetthe future challenges of rice productivity has beendemonstrated in China. In India, so far, 59 ricehybrids have been released by both public and privatesectors and area under hybrid rice reached 2.3 millionhectares, indicating positive trend in adopting hybridrice technology (Viraktamath et al. 2014). The grow-ing acreage of rice hybrids cultivation raises the con-cern of their reaction to biotic stresses. The diseasessuch as blast, bacterial leaf blight, false smut, sheathblight and rice tungro are major rice diseases in India.Rice tungro virus (RTV) disease is one of the mostimportant viral diseases of rice in South and South-East Asia (Azzam and Chancellor 2002). When plantsare infected with RTV in the early seedling stage, yieldlosses can be as high as 100 per cent (Muralidharanet al. 2003a; Periasamy et al. 2006). In India, thedisease is more prevalent in eastern and southernregions and occurred as epidemic during 1984, 1988,1990 and 2001 (Muralidharan et al. 2003b). This is acomplex disease caused by two viruses namely Ricetungro bacilliform virus (RTBV) and Rice tungro sphericalvirus (RTSV) (Hibino et al. 1978). RTSV has a genomeof polyadenylated single-stranded RNA of approxi-mately 10 kb (Jones et al. 1991; Sailaja et al. 2013),whereas RTBV contains double-stranded circular DNAof approximately 8.0 kb (Hay et al. 1991; Mangrauthiaet al. 2012). Tungro viruses are transmitted through