Screening for RYMV resistance using insect vectors

1. Screening for RYMV resistance using insect vectors A. Onasanya1, F.E. Nwilene1, Y. Séré1, E. M. Abo2 1Africa Rice Center (WARDA) 2National Cereals Research Institute Africa Rice Congress 31 July – 4 August 2006, Dar es Salaam, Tanzania

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

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

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

5. 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

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

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

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

9. 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 ?

10. Methodology Differential rice genotype used

11. Identity of RYMV isolates from Nigeria

12. I8 Highly Pathogenic I1 I7 I5 I4 Mildly Pathogenic I6 I2 I3 Virulent strainselection • 3 isolates ( I1, I7 &I8 ) were highly pathogenic and virulent • I7 isolate was selected for use in insect vector screening study

13. Insect species capable of transmitting RYMV from rice plants to alternative (weed) hosts after 48 hrs acquisition feeding period Insect species Alternative (weed) hosts Control Annual Perennial B189 Dig Elu Bra Eco Ecp Olo Leh Imc 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

14. 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 : I7 from Nigeria • Data collection (42 days after inoculation): • - % disease incidence (visual score on a scale of 1-9) • % viral content (ELISA) • % yield reduction

15. POTS LAYOUT V6 V1 V8 V2 Rep 1 V5 V3 V4 V7 V7 V4 V2 V5 Rep 2 V8 V3 V6 V1 V8 V6 V1 V5 Rep 3 V7 V4 V2 V3 = 1m Infected rows (BG 90-2) Test entries

16. Results ANOVA for viral content (VC), disease incidence (DI) and Yield reduction (YR) ns = not significant; * = significant at 5% level ** = significant at 1% level

17. 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 647F4-56 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 % viral content

18. Genotype Insect Mechanical MEAN Gigante (RCK) 19.7 22.2 23.4 Bouake 189 (SCK) 24.7 66.7 43.2 FARO 11 9.9 44.6 27.2 Moroberekan 14.8 44.9 29.9 LAC 23 19.7 45.3 32.5 ITA 235 19.7 36.7 28.2 PNA 647F4-56 55.6 58.9 57.2 H 232-44-1-1 9.9 44.4 27.2 MEAN 21.7 45.5 33.6 Mean comparison for % disease incidence

19. Genotype Insect Mechanical MEAN Gigante (RCK) 28.6 69.7 49.1 Bouake189(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 647F4-56 71.2 77.9 74.6 H 232-44-1-1 18.8 69.0 43.9 MEAN 41.1 77.8 59.5 Mean comparison for % yield reduction

20. 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

21. 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

22. 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

23. Thank you Merci Asante sana Obrigado Melesi

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