Download Inheritance of resistance to rice tungro spherical virus in rice (Oryza

Inheritance of resistance to rice tungro spherical virus
in rice (Oryza sativa L.)
M. Shahjahan, T. Imbe, B.S. Jalani, A.H. Zakri, and O. Othman
Abstract
Three rice varieties resistant to rice tungro spherical virus (RTSV) and on susceptible variety
were used to determine the mode of inheritance of RTSV resistance and the allelic relationships
of the genes involved. Varieties Utri Merah, Kataribhog, and Pankhari 203 were found to be
completely resistant to RTSV. To assess resistant and susceptible seedlings, enzyme-linked
immunosorbent assay was employed. F1 populations invariably showed susceptibility to RTSV.
The F2 data suggest a single recessive gene for resistance in Utri Merah, whereas resistance in
Kataribhog and Pankhari 203 is controlled by three complementary recessive genes.
Resistance in Kataribhog and Pankhari 203 appears to be allelic, whereas the single recessive
gene of Utri Merah is nonallelic to the genes in Kataribhog and Pankhari 203.
Introduction
Tungro, known as penyakit merah (red disease) in Malaysia, is one of the most widespread and
destructive rice viral diseases in Southeast Asia. The disease is attributed to the rice tungro
bacilliform virus (RTBV) and the rice tungro spherical virus (RTSV); RTBV causes the disease
and RTSV intensifies it (Hibino et al 1978). The dearth of information on the inheritance of
resistance to the disease is probably the main reason for the absence of a modern high-yielding
cultivar resistant to it. Identification of resistance sources, detection of genes, and information
about the inheritance of resistance are prerequisites to a successful breeding program. The
present study was undertaken to collect information on the inheritance of RTSV resistance in
rice.
Materials and methods
Three tungro-resistant varieties—Utri Merah, Kataribhog, and Pankhari 203 (Ling 1979)—were
crossed with TN1, a highly susceptible variety, during the 1985 main season at the Malaysian
Agricultural Research and Development Institute, Bumbong Lima, Seberang Perai. In addition,
crosses were made among the resistant varieties to study their allelic relationships. F2 and F3
seeds were produced in subsequent seasons and used in this study. Green leafhopper (GLH)
Nephotettix virescens that had been reared on TN1 for more than 100 generations was used as
the vector for the virus. RTSV was inoculated on 10-day-old seedlings of F1 and F2 populations
and on the parental materials by caging 2 viruliferous vectors (after an acquisition access period
of 24 hours) with individual seedlings in glass chimneys. The same method was followed to
inoculate RTSV into F3 families, but instead of 2 viruliferous vectors, 40 were placed with
individual families of 20 seedlings in mylar cages. In combinations where Pankhari 203, a GLHresistant variety having the Glh-1 gene, was involved, the Pankhari 203 vector biotype was used
to eliminate the vector resistance factor. Three weeks after inoculation, the seedlings were
assessed individually for RTSV infection by enzyme-linked immunosorbent assay (ELISA).
However, the seedlings of each F3 family were pooled to facilitate the detection of homozygous
resistant families. For convenience of presentation, the actual values of RTSV concentration
from the ELISA reader were divided by the value of controlled samples of each microplate, then
multiplied by 100. Antiserum for RTSV was supplied by T. Omura, National Agriculture
Research Center, Tsukuba, Japan.
Results
Kataribhog, Utri Merah, and Pankhari 203 invariably showed complete resistance to RTSV. All
seedlings of these varieties showed zero concentration of RTSV compared with 95.3 in TN1
(Table 1). The F1 progenies of all crosses had RTSV infection (Table 2), and the RTSV
concentration was nearly as high as that in the susceptible parent (Table 3), suggesting that
RTSV resistance in Utri Merah, Kataribhog, and Pankhari 203 is recessive. The F2 populations
of the three crosses did not segregate in the same mode. In Utri Merah/TN1, the ratio of
resistant to susceptible seedlings fit 1:3 (Table 4), indicating that a single recessive gene is
responsible for RTSV resistance in Utri Merah.
Data from F3 families of this combination confirmed the F2 findings (Table 5). It was not possible
to classify the infected families into segregating and homozygous susceptibles, because
seedlings of each family were assessed together, not individually by ELISA, and only
homozygous resistant families were detected. The F2 and F3 data fit the 1:3 ratio (p > 0.30 and p
> 0.50, respectively, Table 4, 5). The frequency distribution of F2 and F3 seedlings with various
levels of RTSV concentration was bimodal, as found in typical Mendelian inheritance (Fig. 1).
The F2 and F3 results of Kataribhog/TN1 showed a satisfactory fit to the 1:63 ratio (p > 0.02 and
p > 0.70, respectively; Table 4, 5), indicating that three complementary recessive genes control
RTSV resistance in Kataribhog. The RTSV concentration in the F2 population also showed a
bimodal distribution (Fig. 2). Likewise, the F2 and F3 results of Pankhari 203/TN1 showed a 1:63
ratio (p < 0.01 and p > 0.70, respectively; Tables 4, 5), implying that three complementary
recessive genes also control RTSV resistance in Pankhari 203. A mode of RTSV concentration
similar to that found in the two other crosses was observed in the F2 population (Fig. 3).
The allelic relationships among resistant varieties are illustrated in Table 6 and Figures 4 and 5.
The data on F1 and F2 populations of Pankhari 203/Kataribhog reveal that the three
complementary recessive genes responsible for RTSV resistance in each of these varieties are
allelic. All 30 F1 seedlings tested from this combination showed complete resistance to RTSV; in
the F2 population, no segregation was observed, and all 280 seedlings tested showed RTSV
resistance (Table 6).
In the two other combinations—Utri Merah/Kataribhog and Utri Merah/Pankhari 203—the F1
populations were totally infected with RTSV; in the F2 populations, the data show a close fit to a
1:3 ratio (p > 0.95; Table 6). The segregations observed in the F2 populations reveal no allelic
relationship between Utri Merah and Kataribhog (Fig. 4), or between Utri Merah and Pankhari
203 (Fig. 5).
Discussion
Studies on the genetics of tungro resistance in rice, based on visual assessment of inoculated
seedlings (IRRI 1966, Lande 1975, Seetharaman et al 1976, Shastry et al 1972), have shown
that resistance is dominant, and that F2 populations inherit in a ratio of 9 resistant: 7 susceptible,
which suggests two pairs of genes having cumulative effects. Most of the resistance sources
used by the authors mentioned above were also resistant to the vector.
RTSV can spread as an independent virus (Aguiero et al 1986). In some cases it is not possible
to distinguish visually seedlings infected with both viruses from those infected with only one.
Therefore, use of a convenient and efficient serological method for proper assessment of
inoculated seedlings is necessary. Although a strong correlation was found between visual
assessment and ELISA (Shahjahan 1989), this relationship may not be critical enough for a
genetic study.
Recent studies by Shahjahan et al (1990) revealed that tolerance for RTBV is a polygenic trait.
However, no information is available about the inheritance of resistance to RTSV. In the present
study, only Utri Merah, Kataribhog, and Pankhari 203 were identified as completely resistant to
RTSV. A single recessive gene was found to be responsible for RTSV resistance in Utri Merah,
a traditional rice variety from Indonesia. We identified Utri Merah as an ideal source of RTSV
resistance (Shahjahan 1989) and showed that the variety is also able to restrict RTBV
multiplication. Kataribhog and Pankhari 203 are also suitable as RTSV resistance sources. It
would be advantageous to use Pankhari 203 as a RTSV resistance source because it is also
resistant to the vector. In addition, varieties resistant to RTSV may be able to inhibit the
transmission of RTBV because the vector is unable to transmit RTBV without acquisition of
RTSV.
References cited
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(RTSV) in Bicol, Philippines. International Rice Research Newsletter 11:17–19.
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disease. Indian Journal of Genetics and Plant Breeding 36:34–36.
Shahjahan M. 1989. Inheritance of resistance to tungro virus in rice (Oryza sativa L.). Ph D
dissertation, Department of Genetics, Universiti Kebangsaan Malaysia. 92 p.
Shahjahan M, BS Jalani, AH Zakri, T Imbe, O Othman. 1990. Inheritance of tolerance to rice
tungro bacilliform virus (RTBV) in rice (Oryza sativa L.). Theoretical and Applied Genetics
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Pages 239–252, In: Rice Breeding. International Rice Research Institute, P.O. Box 933, Manila,
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Notes
Authors’ addresses: M. Shahjahan, B.S. Jalani, and A.H. Zakri, Department of Genetics,
Universiti Kebangsaan Malaysia, Bangi, Malaysia; T. Imbe, Tropical Agriculture Research
Center, Tsukuba, Japan; O. Othman, Malaysian Agricultural Research and Development
Institute (MARDI), Bumbong Lima, Seberang Perai, Malaysia. Acknowledgments: We
appreciate the helpful suggestions of H. Habibuddin of MARDI.
Citation:
Shahjahan M, T Imbe, BS Jalani, AH Zakri, O Othman. 1991. Inheritance of resistance to rice
tungro spherical virus in rice (Oryza sativa L.). pp. 247-254. In: Rice Genetics II. Second
International Rice Genetics Symposium 14-18 May 1990. International Rice Research Institute,
P.O. Box 933, Manila, Philippines. 844 pp.