DETECTION OF RICE TUNGRO BACILLIFORM VIRUS BY POLYMERASE CHAIN-REACTION FOR ASSESSING MILD INFECTION OF PLANTS AND VIRULIFEROUS VECTOR LEAFHOPPERS

The polymerase chain reaction (PCR) was 10(3)-10(4) times more sensiti ve for detecting rice tungro bacilliform virus (RTBV) DNA extracted fr om infected rice plants than was enzyme-linked immunosorbent assay (EL ISA). The greater sensitivity of PCR enabled the detection of the viru s in individual RTBV-exposed leafhoppers, Nephotettix virescens, a sem ipersistent vector of RTBV. Detection of RTBV in the vector by ELISA h as been impossible. To evaluate resistance to RTBV, seedlings of rice cultivars Utri Merah, Utri Rajapan, or Balimau Putih, were inoculated with RTBV, and infection of the cultivars with the virus was indexed b y PCR and ELISA. When inoculated seedlings with no clear symptoms were tested by ELISA, only some seedlings of the three cultivars produced positive reactions, and their ELISA values were generally low. When DN A extracted from the same leaf samples was amplified by PCR, RTBV DNA was detected in all plants that reacted in ELISA. In addition, among t he plants that produced ELISA values lower than 0.05, a value twice th e average of the uninfected controls and considered noninfected with R TBV, 19% of Utri Merah, 4.2% of Utri Rajapan, and 60% of Balimau Putih plants were positive according to PCR. These results indicate that EL ISA failed to detect RTBV in many infected rice plants with tolerance to the virus. The results clearly demonstrate the effectiveness of PCR as a method for evaluating rice cultivars for tolerance or resistance to RTBV.