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Preliminary analysis of genetic variationof rice tungro spherical virusin the PhilippinesK.M.L. Umadhay, M.L.M. Yambao, and O. AzzamThis study investigates the genetic variability of rice tungro spherical virus(RTSV) in nine tungro-endemic sites of the Philippines and over the 1996wet season and 1997 wet and dry seasons. Based on a reverse transcriptase-polymerasechain reaction technique (RT-PCR) followed by restrictionenzyme analysis, six distinct genotypes of RTSV were identified andtheir frequency across all sites determined. Results showed that morethan one genotype could exist in a plant and at least two RTSV genotypesare present at one site. Although RTSV population did not change duringthe sampling, the presence of mixed infections and minor genotypes suggestthat the structure and composition of the virus population is not stable.it is essential to continue monitoring these populations over an extendedperiod to identify factors that lead to virus outbreaks or extinction of thecurrent prevailing populations. This approach is critical in achieving durablevirus resistance.In the tungro disease complex, rice tungro spherical virus assists in the semipersistenttransmission of rice tungro bacilliform virus (RTBV). the other component. whichcauses tungro symptoms. Earlier studies showed that rice varieties react differently toRTSV variants. Recently, polymorphic molecular markers were developed to differentiatetwo variants of RTSV, RTSV-A and RTSV-Vt6 (Yambao et al 1998). Thesevariants are serologically indistinguishable. The molecular markers are based on theamplification of coat protein regions 1 and 2 (CP1 and CP2) of the viral genomeusing reverse transcriptase-polyinerase chain reaction (RT-PCR) followed by a restrictionanalysis of the PCR product. Using this method, the genetic variation ofRTSV natural populations in tungro-endemic regions of the Philippines was investigatedin 1996 and 1997.MethodsNine tungro-endemic sites were sampled during the 1996 wet season (96 WS) and1997 dry and wet seasons (97 DS and WS). Figure 1 shows the sampling sites. Allsamples were tested by enzyme-linked immunosorbent assay (ELISA) against bothRTBV and RTSV antisera and ELISA-positive samples for RTSV were processed byKT-PCR and restriction analysis. The RT-PCR of CP regions 1 and 2 included (1)extraction of total RNA using trizol reagent. (2) cDNA synthesis using Superscript II,and (3) PCR using the cDNA as a template mixed with a cocktail of the followingreagents: Taq DNA polymerase. primers. MgC12, dNTP mixture, and buffer. The reactionconditions were initial denaturation at 95 °C for 3 min. denaturation at 95 °Cfor 1 min. annealing temperature of 50 °C for 1 min. extension of68 °C for 5 min, andfinal extension of 72 °C for 7 min. The generated PCR products were then digested
Fig. 1. Sampling sites in tungro-endemic provinces of the Philippines. Planting seasons and ricevarieties are indicated on the right side.with Hind III and Bst Y I restriction enzymes and run on 1% agarose gel stained withethidium bromide (Table 1).Results and discussionSix distinct coat protein genotypes were identified in the initial 302 analyzed samplesfrom North Cotabato, Nueva Ecija, and Bicol provinces during the 1996 WS and DS,and 1997 WS. The frequency of each coat protein genotype was used as a potentialindicator of virus variation per location (Fig. 2). In Nueva Ecija and Bicol, coat proteingenotypes II, III, and VI were observed. In North Cotabato, coat protein genotypesII, III, V, and VI were found in the 1997 DS while coat protein genotypes I, II,18 Umadhay et al
Page 2 and 3: RiceTungro DiseaseManagementEdited
Page 4 and 5: ContentsRice tungro disease in the
Page 6 and 7: ForewordThe intensification of rice
Page 8 and 9: PrefaceProviding farmers with optio
Page 10 and 11: Rice tungro disease in the Philippi
Page 12 and 13: Cotabato, and Laguna) during 1995-9
Page 14 and 15: seed growers and farmers to increas
Page 16 and 17: Fig. 2. Incidence of rice tungro di
Page 18 and 19: De los Reyes JB, Cabunagan, RC, Col
Page 20 and 21: Preliminary analysis of genetic var
Page 22 and 23: Fig. 2. Distinct rice tungro bacill
Page 24 and 25: Fig. 4. Dendogram depicting the rel
Page 28 and 29: Table 1. Size characteristics of th
Page 30 and 31: varieties and did not seem to exert
Page 32 and 33: Developing breeding lines with RTD
Page 34 and 35: In CES, 28 entries had low tungro i
Page 36 and 37: Table 2. Best rice tungro disease-r
Page 38 and 39: Breeding for rice tungro virus resi
Page 40 and 41: Table 2. Promising lines resistant
Page 42 and 43: Table 4. Rice cultivars used as hyb
Page 44 and 45: Shahjahan MB, Jalani S, Zakri AH, I
Page 46 and 47: Table 1. Initial 19 transgenic line
Page 48 and 49: Table 4. Percent infection of trans
Page 50 and 51: very low level. In fact, transgene
Page 52 and 53: of Agricultural Research (ICAR). Pr
Page 54 and 55: Fig. 2. Mean infection with rice tu
Page 56 and 57: (RTBV) and rice tungro spherical vi
Page 58 and 59: Table 4. Percent infection a with r
Page 60 and 61: GLH numbers were much lower on IR62
Page 62 and 63: Cabunagan RC, Hibino H, Sama S, Riz
Page 64 and 65: Prospects of virus-resistant variet
Page 66 and 67: Tungro in Bali (1987-97)Tungro infe
Page 68 and 69: Fig. 5. Proportion of varieties gro
Page 70 and 71: Table 3. Percent incidence of rice
Page 72 and 73: Evaluating rice germplasm for resis
Page 74 and 75: Table 2. Percent infection a with r
Page 76 and 77:
Rice tungro disease resistance andm
Page 78 and 79:
Table 1. Percent infection a with r
Page 80 and 81:
ecommended vector-resistant variety
Page 82 and 83:
Materials and methodsBatches of ant
Page 84 and 85:
ReferencesClark MF, Adams AN. 1977.
Page 86 and 87:
(e.g., Sokal and Rohlf 1995, p 213;
Page 88 and 89:
Surveillance scheme for tungro fore
Page 90 and 91:
entrusted with implementing the pro
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Table 1. Number of mobile nursery t
Page 94 and 95:
are implemented immediately. The co
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Farmers’ rice tungro managementpr
Page 98 and 99:
Experience with tungroAlthough both
Page 100 and 101:
Table 5. Farmers (%) reporting tung
Page 102 and 103:
Table 7. Farmers’ reported tungro
Page 104 and 105:
Table 9. Mean number (standard devi
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than rice), so they may be reluctan
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Community-based rice pest managemen
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Establishment of farmers’ indigen
Page 112 and 113:
Meanwhile, insects, diseases, and n
Page 114 and 115:
Table 2. Most important diseases fo
Page 116 and 117:
Farmers’ knowledge of pest contro
Page 118 and 119:
ha -1 and above) had a lower RTD in
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Fig. 4. Three major peaks of green
Page 122 and 123:
RBB hill -1 and 4% WSB (Fig. 6). In
Page 124 and 125:
The influence of varietal resistanc
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Limited data exist on how resistant
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tember plantings, reaching 13% and
Page 130 and 131:
Holt J, Chancellor TCB, Reynolds DR
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glh4, respectively. Planting at the
Page 134 and 135:
Results and discussionMinimum unit
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Fig. 4. Transmission efficiency of
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Table 1. Enzyme-linked immunosorben
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Leafhopper control by insecticides
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Fig. 1. Cartoon used for tungro man
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The role of vector control in rice
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To establish relationships between
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Fig. 1. Influence of antifeedants o
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Fig. 4. Tungro incidence before har
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ReferencesAryawan IGN, Widiarta IN,
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Materials and methodsSeedbed protec
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Table 2. Relationship of RTD incide
Page 158 and 159:
Management of rice tungro disease b
Page 160 and 161:
Results and discussionGLH populatio
Page 162 and 163:
Table 4. Field evaluation of foliar
Page 164 and 165:
3.6 to 2.7 t ha -1 . These yields w
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