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 Congress31 July – 4 August 2006, Dar es Salaam, Tanzania

OUTLINE

IntroductionIntroduction

Management StrategyManagement Strategy

Key IssuesKey Issues

MethodologyMethodology

Results Results

SummarySummary

The Way ForwardThe Way Forward

Distribution of RYMV in Africa

MauritaniaSenegal

Gambia Guinea Bissau

GuineaSierra Leone

Burkina Faso

Mali

Liberia

Côte d’Ivoire

GhanaTogo

Benin

Nigeria

ChadNiger

Kenya

Tanzania

MadagascarCameroon

Rwanda

Countries with RYMV incidenceCountries with RYMV incidence

Endemic countriesEndemic countries

Varietal resistance

Alternative host management

Vector management

Cultural

practices

Strategy for Integrated Management of RYMV

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 soilWeeding operations with hoesHarvesting with sickleInsects

11

22

33

feed on an infected plantfeed on an infected plant

collect the virus particlescollect the virus particles

pass them on to the next plant that they pass them on to the next plant that they feed onfeed on

The virus does not undergo any changes The virus does not undergo any changes within the insect itself, but simply uses it as within the insect itself, but simply uses it as a vehiclea vehicle

The insect speciesThe insect species

Why focus on insect vectors ?

Chaetocnema pulla Trichispa sericea Oxya hyla

Locris rubra Conocephalus longipennisChnootriba similis

Insect vectors of RYMV

Nature of damage of rice leaves by vectors

1. Chaetocnema pulla2. Trichispa sericea3. Oxya hyla

1 2 3 4 5

4. Chnootriba similis5. Conocephalus longipennis

• Why do we want to modify our Why do we want to modify our screening methodology by using insect screening methodology by using insect vectors in place of conventional vectors in place of conventional mechanical inoculation ?mechanical inoculation ?

•Why in a uniform field of rice, only Why in a uniform field of rice, only some plants become diseased ?some plants become diseased ?

Key Issues

•High yielding rice varieties with stable High yielding rice varieties with stable resistance to RYMV are not yet availableresistance to RYMV are not yet available

Differential rice genotype usedCode Genotype O. sativa

typeOrigin

V1 Gigante – resist. check Indica Mozambique

V2 Bouaké 189 – sus. check Indica Côte d’Ivoire

V3 FARO 11 (OS 6) Japonica Nigeria

V4 Moroberekan Japonica Côte d’Ivoire

V5 LAC 23 Japonica Liberia

V6 ITA 235 Japonica Nigeria

V7 PNA 647F4-56 Japonica Peru

V8 H 232-44-1-1 Indica Argentina

Methodology

Identity of RYMV isolates from Nigeria

Isolate Code

Location Region Host Plant Ecology

I1 Vovogi Tsaragi Kwara State

FARO 43 Upland

I2 Takonicha Tsaragi

Kwara State

FARO 29 Upland

I3 Ogbese-Akure Ondo State  Cultivated Lowland

I4 IITA-Ibadan Oyo State BR 519-9 (FKR 24) Irrigated

I5 IITA-Ibadan Oyo State AZUCENA (WHITE) Irrigated

I6 IITA-Ibadan Oyo State B 2161-CMR 57-1-3-1

Irrigated

I7 IITA1 Oyo State IR5 Lowland

I8 IITA2 Oyo State IR5 Lowland

Virulent strain selection

I4

I6

I1

I7

I5

I8

I2

I3

Highly Pathogenic

Mildly Pathogenic

3 isolates ( I1, I7 & I8 ) were highly pathogenic and virulent

- I7 isolate was selected for use in insect vector screening study

Insect species capable of transmitting RYMV from rice plants to alternative (weed) hosts after 48 hrs acquisition feeding period

Imc

Locris rubra

Cofana unim.

Cofana spectra

Sucking bug

Zonocerus

Parattetix

Euscyrtus

Oxya hyla

Conocephalus

L.F. g/hopper

Cheilomenes

Chnootriba simil.

Trichispa seric.

Chaetocnema pul.

L.F. beetles

LehOloEcpEcoBraEluDigB189

PerennialAnnualControlAlternative (weed) hostsInsect species

•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

•RYMV Isolate : I7 from Nigeria

•Infected rows : BG 90-2

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

Methodology (cont.)

Infected rows(BG 90-2)

Test entries

= 1m

V6V1V8V2 Rep 1V5V3V4V7

V7V4V2V5 Rep 2V8V3V6V1

V8V6V1V5 Rep 3V7V4V2V3

POTS LAYOUT

Results

ns = not significant; * = significant at 5% level ** = significant at 1% level

Source d.f. F value

VC DI YRRep 2 <1 <1 2.9 ns

Genotype (G) 7 1.3 ns 3.2 * 5.4 **

Method (M) 1 965.7 ** 29.9 ** 75.6 **

G x M 7 1.2 ns 1.9 ns 2.0 ns

Error 30

Total 47

ANOVA for viral content (VC), disease incidence (DI) and Yield reduction (YR)

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

Mean comparison for % disease incidence

Genotype Insect Mechanical MEANGigante (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

Genotype Insect Mechanical MEANGigante (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

Screening with mechanical inoculation produced:

7.8% viral content45.5% disease incidence77.8% yield reduction

Summary

Screening with insect vector produced:45.2% viral content21.7% disease incidence41.1% yield reduction

•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

Summary (cont.)

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

The Way Forward

Thank you

Merci

Asante sana

Obrigado

Melesi

No flowering or some plants dead

>75%Leaves turn yellow orange

Highly susceptible

9

delayed26-75%Pale yellow leaves

Susceptible 7

Slightly delayed

6-25%Pale green with mottling

Moderately resistant

5

normal<5% reduction

Green leaves with sparse dots

Resistant 3

normalnilgreen High.resistant 1

FloweringReduction in plant height

Leaf colorResistant type

Visual

score

Levels of resistance / susceptibility

RYMV Evaluation System (IITA, 1986)