Search

Rice tungro disease (RTD) is caused by Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus (RTBV) transmitted by green leafhoppers. Rice cv. Utri Merah is highly resistant to RTD. To define the RTD resistance of Utri Merah, near-isogenic lines (NIL, BC5 or BC6) developed from Utri Merah and susceptible cv. Taichung Native 1 (TN1) were evaluated for reactions to RTSV and RTBV. TW16 is an NIL (BC5) resistant to RTD. RTBV was able to infect both TN1 and TW16 but the levels of RTBV were usually significantly lower in TW16 than in TN1. Infection of RTSV was confirmed in TN1 by a serological test but not in TW16. However, the global gene-expression pattern in an RTSV-resistant NIL (BC6), TW16-69, inoculated with RTSV indicated that RTSV can also infect the resistant NIL. Infection of RTSV in TW16 was later confirmed by reverse-transcription polymerase chain reaction but the level of RTSV was considerably lower in TW16 than in TN1. Examination for virus accumulation in another NIL (BC6), TW16-1029, indicated that all plants of TW16-1029 were resistant to RTSV, whereas the resistance to RTBV and symptom severity were segregating among the individual plants of TW16-1029. Collectively, these results suggest that RTD resistance of Utri Merah involves suppression of interacting RTSV and RTBV but the suppression trait for RTSV and for RTBV is inherited separately.

Rice tungro disease (RTD) is caused by the interaction between Rice tungro spherical virus (RTSV) and Rice tungro bacilliform virus (RTBV), both of which are transmitted by green leafhoppers (GLH). In order to define the resistance against RTD in rice cv. Matatag 9 which was developed by interspecific hybridization between RTD-susceptible cv. IR64 and Oryza rufipogon, the reactions of Matatag 9 to the viruses and GLH were evaluated in comparison with RTD-susceptible and -resistant rice cultivars. The incidences of infection with RTSV and RTBV in Matatag 9 were significantly lower than those in the susceptible parent cv. IR64; however, no substantial differences in virus accumulation were observed between IR64 and Matatag 9 once infected with the viruses. Symptoms in Matatag 9 infected with RTBV and RTSV were milder than those observed in IR64. A higher level of antixenosis to GLH was observed in Matatag 9 compared with IR64. The levels of antibiosis against GLH in Matatag 9 were comparable with those in another GLH-resistant cultivar, and significantly higher than those in RTD-susceptible cultivars. Collectively, these results suggest that tolerance to tungro viruses and resistance to GLH both contribute to the apparent resistance to RTD in Matatag 9, although possible involvement of other resistance mechanisms cannot be excluded.

Tungro is a composite disease of rice induced by dual infection with rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). Four strains of RTBV, designated L, G1, G2, and Ic, were isolated on the basis of their characteristic symptoms on rice cultivars FK135 and Taichung Native 1 (TN1). On FK135, strain Ic caused severe stunting, reduced tillering, narrow leaves, and distinct interveinal chlorosis (striping and/or mottling) on the leaf blades, while G1 and G2 caused only mild stunting and foliage was a normal green. On TN1, G1 and Ic caused mild stunting but no discoloration of the foliage; G2 caused severe stunting and yellow to orange discoloration similar to that caused by the type strain L. Thus, G1 and Ic can be readily differentiated by the reaction of cultivar FK135, while G1 and G2 can be differentiated by that of TN1. Cross-inoculation experiments showed that strains G1 and Ic were cross protective. In other studies, a virulent strain of RTSV (Vt6) was isolated from tungro-infected plants collected from Mindanao, Philippines. The cultivar TKM6, like many other cultivars resistant to type strain A, was susceptible to strain Vt6. TKM6 plants infected with both RTBV and strain Vt6 showed severe stunting and discoloration

The polymerase chain reaction (PCR) was 103-104 times more sensitive for detecting rice tungro bacilliform virus (RTBV) DNA extracted from infected rice plants than was enzyme-linked immunosorbent assay (ELISA). The greater sensitivity of PCR enabled the detection of the virus in individual RTBV-exposed leafhoppers, Nephotettix virescens, a semipersistent vector of RTBV. Detection of RTBV in the vector by ELISA has 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 by PCR and ELISA [...]

Nucleic acids and proteins of rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV) were analyzed by gel electrophoresis. RTSV contains single-stranded RNA of 3.7×10 6 Da and two major proteins of 24 and 23 kDa. RTBV contains circular double-stranded DNA of 8.3 kbp and a single major protein of 32 kDa. The RTBV-DNA is 2.1-2.3 μm in length and has two discontinuities, one in each of the two strands, having different polarities. Endonuclease cleavage sites in the RTBV-DNA molecule are mapped (...)