Скачать презентацию Screening for RYMV resistance using insect vectors A Скачать презентацию Screening for RYMV resistance using insect vectors A

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Screening for RYMV resistance using insect vectors A. Onasanya 1, F. E. Nwilene 1, Screening for RYMV resistance using insect vectors A. Onasanya 1, F. E. Nwilene 1, Y. Séré 1, E. M. Abo 2 1 Africa Rice Center (WARDA) 2 National Cereals Research Institute Africa Rice Congress 31 July – 4 August 2006, Dar es Salaam, Tanzania

OUTLINE Introduction Management Strategy Key Issues Methodology Results Summary The Way Forward OUTLINE Introduction Management Strategy Key Issues Methodology Results Summary The Way Forward

Distribution of RYMV in Africa Burkina Faso Mauritania Senegal Gambia Guinea Bissau Guinea Sierra Distribution of RYMV in Africa Burkina Faso Mauritania Senegal Gambia Guinea Bissau Guinea Sierra Leone Mali Niger Chad Benin Ghana Togo Côte d’Ivoire Nigeria Liberia Kenya Rwanda Tanzania Cameroon Madagascar Countries with RYMV incidence Endemic countries

Strategy for Integrated Management of RYMV Cultural practices Varietal resistance Vector management Alternative host Strategy for Integrated Management of RYMV Cultural practices Varietal resistance Vector management Alternative host management

How is the virus transmitted? The virus is mechanically transmitted – gains entry into How is the virus transmitted? The virus is mechanically transmitted – gains entry into rice plants through injuries. The possible roots of entry are: Root damage during transplanting and roots intertwining in the soil Weeding operations with hoes Harvesting with sickle Insects

Why focus on insect vectors ? The insect species 1 feed on an infected Why focus on insect vectors ? The insect species 1 feed on an infected plant 2 collect the virus particles 3 pass them on to the next plant that they feed on The virus does not undergo any changes within the insect itself, but simply uses it as a vehicle

Insect vectors of RYMV Chaetocnema pulla Chnootriba similis Trichispa sericea Conocephalus longipennis Oxya hyla Insect vectors of RYMV Chaetocnema pulla Chnootriba similis Trichispa sericea Conocephalus longipennis Oxya hyla Locris rubra

Nature of damage of rice leaves by vectors 4. Chnootriba similis 5. Conocephalus longipennis Nature of damage of rice leaves by vectors 4. Chnootriba similis 5. Conocephalus longipennis 1. Chaetocnema pulla 2. Trichispa sericea 3. Oxya hyla 1 2 3 4 5

Key Issues • High yielding rice varieties with stable resistance to RYMV are not Key Issues • High yielding rice varieties with stable resistance to RYMV are not yet available • Why do we want to modify our screening methodology by using insect vectors in place of conventional mechanical inoculation ? • Why in a uniform field of rice, only some plants become diseased ?

Methodology Differential rice genotype used Code Genotype Origin V 1 V 2 O. sativa Methodology Differential rice genotype used Code Genotype Origin V 1 V 2 O. sativa type Gigante – resist. check Indica Bouaké 189 – sus. check Indica Mozambique Côte d’Ivoire V 3 FARO 11 (OS 6) Japonica Nigeria V 4 Moroberekan Japonica Côte d’Ivoire V 5 LAC 23 Japonica Liberia V 6 ITA 235 Japonica Nigeria V 7 PNA 647 F 4 -56 Japonica Peru V 8 H 232 -44 -1 -1 Indica Argentina

Identity of RYMV isolates from Nigeria Location Region Host Plant Ecology I 1 Vovogi Identity of RYMV isolates from Nigeria Location Region Host Plant Ecology I 1 Vovogi Tsaragi Kwara State FARO 43 Upland I 2 Takonicha Tsaragi Kwara State FARO 29 Upland I 3 Ogbese-Akure Ondo State Cultivated Lowland I 4 IITA-Ibadan Oyo State BR 519 -9 (FKR 24) Irrigated I 5 IITA-Ibadan Oyo State AZUCENA (WHITE) Irrigated I 6 IITA-Ibadan Oyo State B 2161 -CMR 57 -1 -31 Irrigated I 7 IITA 1 Oyo State IR 5 Lowland I 8 IITA 2 Oyo State IR 5 Lowland Isolate Code

Virulent strain selection I 8 Highly Pathogenic 3 isolates ( I 1, I 7 Virulent strain selection I 8 Highly Pathogenic 3 isolates ( I 1, I 7 & I 8 ) were highly pathogenic and virulent I 1 I 7 I 5 I 4 I 6 I 2 I 3 Mildly Pathogenic - I 7 isolate was selected for use in insect vector screening study

Insect species capable of transmitting RYMV from rice plants to alternative (weed) hosts after Insect species capable of transmitting RYMV from rice plants to alternative (weed) hosts after 48 hrs acquisition feeding period Insect species L. F. beetles Chaetocnema pul. Trichispa seric. Chnootriba simil. Cheilomenes L. F. g/hopper Conocephalus Oxya hyla Euscyrtus Parattetix Zonocerus Sucking bug Cofana spectra Cofana unim. Locris rubra Control B 189 Dig Alternative (weed) hosts Annual Perennial Elu Bra Eco Ecp Olo Leh Imc

Methodology (cont. ) • Experimental design: RCB with 3 replications • Insect vector used Methodology (cont. ) • Experimental design: RCB with 3 replications • Insect vector used : Oxya hyla reared on BG -2 in a paddy screen house • Cultivar used : 8 differential rice genotypes • Infected rows : BG 90 -2 • RYMV Isolate : I 7 from Nigeria Data collection (42 days after inoculation): - % disease incidence (visual score on a scale of 1 -9) - % viral content (ELISA) - % yield reduction

POTS LAYOUT V 6 V 1 V 8 V 2 V 5 V 3 POTS LAYOUT V 6 V 1 V 8 V 2 V 5 V 3 V 4 V 7 V 4 V 2 V 5 V 8 V 3 V 6 V 1 V 8 V 6 V 1 V 5 V 7 V 4 V 2 V 3 = 1 m Infected rows (BG 90 -2) Test entries Rep 1 Rep 2 Rep 3

Results ANOVA for viral content (VC), disease incidence (DI) and Yield reduction (YR) Source Results ANOVA for viral content (VC), disease incidence (DI) and Yield reduction (YR) Source d. f. Rep Genotype (G) Method (M) Gx. M Error 2 7 1 7 30 Total F value DI YR 47 VC <1 1. 3 ns 965. 7 ** 1. 2 ns <1 3. 2 * 29. 9 ** 1. 9 ns ns = not significant; * = significant at 5% level ** = significant at 1% level 2. 9 ns 5. 4 ** 75. 6 ** 2. 0 ns

Mean comparison for % viral content Genotype Insect Mechanical MEAN Gigante (RCK) 47. 1 Mean comparison for % viral content Genotype Insect Mechanical MEAN Gigante (RCK) 47. 1 9. 6 28. 3 Bouake 189 (SCK) 43. 5 14. 2 28. 9 FARO 11 43. 2 6. 4 24. 8 Moroberekan 43. 6 5. 8 24. 7 LAC 23 47. 6 6. 0 26. 8 ITA 235 48. 2 6. 8 27. 5 PNA 647 F 4 -56 42. 0 4. 6 23. 3 H 232 -44 -1 -1 46. 6 8. 5 27. 6 MEAN 45. 2 7. 8 26. 5

Mean comparison for % disease incidence Genotype Insect Mechanical MEAN Gigante (RCK) Bouake 189 Mean comparison for % disease incidence Genotype Insect Mechanical MEAN Gigante (RCK) Bouake 189 (SCK) FARO 11 Moroberekan LAC 23 ITA 235 19. 7 24. 7 9. 9 14. 8 19. 7 22. 2 66. 7 44. 6 44. 9 45. 3 36. 7 23. 4 43. 2 27. 2 29. 9 32. 5 28. 2 PNA 647 F 4 -56 H 232 -44 -1 -1 MEAN 55. 6 9. 9 21. 7 58. 9 44. 4 45. 5 57. 2 27. 2 33. 6

Mean comparison for % yield reduction Genotype Insect Mechanical MEAN Gigante (RCK) 28. 6 Mean comparison for % yield reduction Genotype Insect Mechanical MEAN Gigante (RCK) 28. 6 69. 7 49. 1 Bouake 189(SCK) 35. 1 98. 0 66. 5 FARO 11 37. 4 75. 0 56. 2 Moroberekan 51. 7 78. 8 65. 3 LAC 23 46. 6 75. 2 60. 9 ITA 235 39. 1 78. 4 58. 8 PNA 647 F 4 -56 71. 2 77. 9 74. 6 H 232 -44 -1 -1 18. 8 69. 0 43. 9 MEAN 41. 1 77. 8 59. 5

Summary Screening with mechanical inoculation produced: 7. 8% viral content 45. 5% disease incidence Summary Screening with mechanical inoculation produced: 7. 8% viral content 45. 5% disease incidence 77. 8% yield reduction Screening with insect vector produced: 45. 2% viral content 21. 7% disease incidence 41. 1% yield reduction

Summary (cont. ) • Insect vector was able to transmit higher viral content than Summary (cont. ) • Insect vector was able to transmit higher viral content than the mechanical inoculation method • Virus pathogenicity (disease incidence and yield reduction) was higher in mechanical inoculation method than in the insect vector

The Way Forward This preliminary study revealed the possibility and potential of using insect The Way Forward This preliminary study revealed the possibility and potential of using insect vector to screen for durable resistance to RYMV. However, information on other vector species is needed to further confirm its potential

Thank you Merci Asante sana Obrigado Melesi Thank you Merci Asante sana Obrigado Melesi

Levels of resistance / susceptibility RYMV Evaluation System (IITA, 1986) Visual score Resistant type Levels of resistance / susceptibility RYMV Evaluation System (IITA, 1986) Visual score Resistant type Leaf color 1 High. resistant green 3 Resistant 5 Moderately resistant Susceptible 7 9 Highly susceptible Green leaves with sparse dots Pale green with mottling Pale yellow leaves Leaves turn yellow orange Reduction Flowering in plant height nil normal <5% reduction normal 6 -25% Slightly delayed 26 -75% >75% No flowering or some plants dead