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1) International Rice Research Institute, P.O. Box 933, 1099 Manila, Philippines
2) Faculty of Agriculture, Kyoto University, Kyoto 606, Japan
Tungro is a complex disease caused by joint infection by rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). Only a few accessions of cultivated rice, O. sativa, are resistant to these viruses. We screened several wild species of rice for resistance to tungro, and found some species including O. officinalis to be resistant to tungro infection. Of these, two accessions of O. officinalis from Thailand, Acc. 105365 and Acc. 100896, showed 0% and low infection with both viruses, respectively. At the International Rice Research Institute, we are maintaining the MAALs of O. sativa (IR31917-45-3-2) having single chromosome of O. officinalis (Acc. 100896) established by Jena and Khush (1989). We screened 9 MAALs for tungro resistance to identify the chromosomal location of the genes governing resistance to tungro derived from O. officinalis.
To identify the alien chromosome with tungro resistance, the trait must be controlled by dominant gene(s). When 10 F1 plants from the cross between a tungro susceptible cultivar TN1 and tungro resistant O. officinalis (Acc. 105365) were grown under natural conditions, no plant was infected with RTSV while 5 plants were infected with RTBV. This suggested that the resistance to RTSV infection in O. officinalis is a dominant trait. Thus, we screened MAALs for tungro resistance to identify the chromosome on which the resistance gene(s) for RTSV infection is located.
Nine of the 12 possible MAALs, the recurrent parent IR31917-45-3-2, the donor parent O. officinalis (Acc. 100896) and a check variety TN1 were tested for tungro incidence under natural field conditions. The test materials were grown in the experimental field at IRRI, Los Banos, the Philippines in 1992 dry season. Two months after transplanting, leaves of each plant were sampled individually to determine if they were infected with RTBV and RTSV, by enzyme-linked immunosorbent assay (ELISA) Bajet et al. 1985). The plants having the additional alien chromosome were identified morphologically (Jena and Khush 1989, 1990).
The O. officinalis accession showed low infection rate with RTBV (30%) and RTSV (3%), while IR31917-45-3-2 was severely infected with RTBV (100%) and RTSV (48%) (Table 1). All 9 MAALs showed high infection rate for RTBV and most of them were susceptible to RTSV. Only MAAL 11 showed low infection rate (17%) with RTSV. These results suggest that the gene for resistance to RTSV infection might be located on chromosome 11 of O. officinalis.
Table 1. Infection rates with RTBV and RTSV of MAALs, the recurrent parent
(IR31917) and the donor parent Oryza officinalis (Acc. 100896).
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Plants Infection rate (%) with
Line tested =================================================
(no.)* RTBV RTSV none
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MAAL 4 43 100 72 0
MAAL 5 8 88 100 0
MAAL 6 18 89 94 0
MAAL 7 44 100 82 0
MAAL 8 33 100 100 0
MAAL 9 20 90 65 5
MAAL 10 15 100 47 0
MAAL 11 23 100 17 0
MAAL 12 19 79 47 16
IR31917-45-3-2 63 100 84 0
O. officinalis 87 39 3 61
TN1 30 87 93 3
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* refers to plants identified morphologically having an additional chromosome
from O. officinalis.
References
Bajet, N. B., R. D. Daquioag and H. Hibino, 1985. Enzyme-linked immunosorbent assay to diagnose rice tungro. J. PI. Prot. Tropics 2: 125-129.
Jena, K. K. and G. S. Khush, 1989. Monosomic alien addition lines of rice: production, morphology, cytology, and breeding behavior. Genome 32: 449-455.
Jena, K. K. and G. S. Khush, 1990. Introgression of genes from Oryza officinalls Wall ex Watt to cultivated rice, O. sativa L. Theor Appl Genet 80: 737-745.
