Viruses, Insects and Hunger

Shivaji Pandey1) and Wafaa El Khoury2)

1) Director, Plant Production and Protection Division, Agriculture and Consumer Protection Department, FAO, Rome, Italy

2) FAO, Rome, Italy Plant Pathologist, Plant Production and Protection Division, Agriculture and Consumer Protection Department, FAO, Rome, Italy

Sixth World Conference on the Future of ScienceViruses: the invisible enemy

Venice, Sept 19-21, 2010

Plant diseases and food security

• Annual losses of about $US 60 billion due to plant diseases

• Lower quantity and quality of agricultural production and hamper international trade through quarantine restrictions

• Aggrevate food insecurity of the poorest: ca 75% of the world’s one billion hungry and poor live in rural areas, deriving livelihoods from agriculture

• About 800 recognized plant viruses, they are a major contributor to these losses

• Serious losses recorded from epidemics of viral diseases on cassava, banana, maize, rice, potato, yam and other staple crops of subsistence farming communities

• Examples of national estimates of losses:– Banana bunchy top virus disease: Malawi, 40% loss in

production – Rice yellow mottle virus: Mali, 64–100% and Niger,58–68% – Cassava mosaic disease: Uganda $60 million every year

(1992-1997)

Plant virus diseases

Losses to national economies are often reasonably well documented and estimated in financial terms....

More difficult to assess are the impacts on local market, livelihoods, farmers’ coping strategies and food security.

Food security exists when all people, at all times, have access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life

Food security

Food security and banana productionIntegrated Food Security Phase Classification (IPC) - September 2008

Importance of banana in the diet

Share of banana in diets����

Temporary and permanent food security

����

High banana dependence +

Low food insecurity =

Is food security dependent on banana?

High banana dependence + High food insecurity =

High priority

Ref: Eden-Green, S. “International Workshop on Banana Bunchy Top Disease and Banana Xanthomonas Wilt: Meeting the Challenges of Emerging Disease Threats to Banana and Strategies for Raising Awareness, Surveillance and Management of these diseases in Sub- Saharan Africa” August 2009, Arusha, Tanzania ,

Emerging infectious plant diseases

Global increase in emerging infectious plant diseases, expressed as:

– increase in incidence, geographical or host range

– changes in pathogenesis

– newly evolving

– newly discovered or identified plant diseases

Major taxa of emerging pathogens (ProMED 1996-2002) Anderson et al. 2004

Virus

47%

Fungi

30%

Bacteria

16%

Nematode

1%Phytoplasma

4%

Unknown

2%

Factors driving emergence of plant diseases 1996 -2002 (ProMED alerts) Anderson et al. 2004

Introductions

56%Weather

25%

Farming

techniques

9%

Recombination

2%

Change in

vector

population

7%

Habitat

disturbances

1%

Evolution and emergence of viruses

Mechanisms involved in process of evolution and emergence of infectious viruses include:

– recombination

– genome integration

– host adaptation

– mutations

– new vector biotypes

– long distance dispersal

Plant virus disease epidemicsEmerging infectious viruses developing into disease epidemics are consistently linked to human-induced changes in agricultural production systems:

– introductions of new crops and introduction of new vulnerable genotypes

– crop intensification and changes in agronomic practices

– germplasm movement

– introduction of a new virus or virus strain (often linked to germplasm movement)

– introduction of a new vector species or biotype (often linked to germplasm movement)

Disease management strategies• Use of virus-free planting material• Roguing and sanitation and other cultural

practices• Host plant resistance (to virus or vector)• Integrated vector management (depends on

transmission relationship)

Crop intensification practices enhancing epidemics of emerging

plant viruses and their implications for disease management strategies

Examples from staple crops in developing countries

Rice Ragged Stunt Virus (RRSV), Rice Grassy Stunt Virus (RGSV) and the Brown Planthopper (BPH) in Asia

RRSV, RGSV and their vector the BPH

Hopperburned fields

RRSV

• RRSV: Stunting and ragged appearance, leaves with serrated edges and twisted blades, delayed panicle emergence and reduced grain filling

• RGSV: Excessive tillering, stunting, grassy rosette appearance, no panicles

• Transmitted by the brown planthopper (BPH) in a circulative propagative way

• BPH a serious pest of rice causing hopperburn symptoms in absence of virus

BPH adults (IRRI)

RGSV

Nilaparvata lugens

• Expansion of cultivation of high yielding varieties packaged with agricultural inputs (pesticides and fertilizers)

• Explosion of the brown planthopper (BPH) population with excessive insecticide use for control

• Explosion of RRSV and RGSV epidemics with the population increase of the BPH vector

RRSV, RGSV and BPH in Asia Crop intensification

Hopperburn in hybrid rice SL7 in PhilippinesPicture credit: C. Bernal (IRRI)

Brown Plant Hopper (BPH)

RRSV, RGSV and BPH in Asia Pest management

• RGSV and RRSV only a problem after BPH outbreaks

• Manage BPH correctly, its viruses will decline

• Insecticides do not stop virus epidemics, non-chemical methods can help;

• BPH outbreaks start from local populations by insecticide overuse their killing natural enemies

• BPH outbreaks continue until natural enemies recover

• Destruction of volunteer crops, rotation, escape based on monitoring of the peak of BPH populations by light traps to adjust planting dates in the field

RRSV, RGSV and BPH in Asia

Host Plant Resistance• Widespread cultivation in tropics of rice cultivars with

RGSV resistance gene (eg from wild rice species Oryza nivara)

• Severe strain of RGSV (RGSV-2) developed in the Philippines highly pathogenic to resistant cultivars derived from O. nivara

• Widespread cultivation of rice cultivars with resistance to BPH vectors in many countries in Asia

• Development of BPH biotypes overcoming resistance a few or several years after cultivar release

Farmers Field Schools

Infected area by virus in Summer cropInfected area by virus in Summer cropInfected area by virus in Summer cropInfected area by virus in Summer cropand Main/Autumn crop (2006)and Main/Autumn crop (2006)and Main/Autumn crop (2006)and Main/Autumn crop (2006)

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Indonesia Rice Production vs. Rice Pesticide Costs

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ucti

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(M

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Presidential Policy 3/86

Effect of pesticide national policy on vector and disease management -Case of Indonesia

Cassava Mosaic Virus Disease (CMD) and Cassava Brown Streak Virus (CBSV) in

SSA

ACMV and EACMV species: discoloration, chlorotic mosaic of leaves; root yield is dramatically reduced (80% losses)

EACMV-UG, genetic recombinant hybrid emerging associated with unusually severe and rapidly spreading epidemics of CMV in E. and C. Africa

Cassava Mosaic Virus Disease (CMD)

Caused by Cassava Mosaic Geminiviruses

Cassava Mosaic Virus Disease (CMDs)

Viruses transmitted through the whitefly Bemisia tabaci

Long distance transmission through infected planting material

Changes in virus-vector interaction

Cassava Mosaic Disease in East Africa

Severely CMD-affected plants in Uganda interact synergistically with Bemisia tabaci populations, resulting in greater virus spread of the pandemic

- increased colonization of infected plants by the whitefly vector

- higher concentration of eggs on symptom-free leaves of diseased plant and

- increased rates of vector fecundity on CMD-infected plants.

Management through

• Resistant varieties• Use of clean vegetative

planting material• Roguing (with low incidence)• Field isolation (when possible)

Cassava Mosaic Virus Disease (CMDs)

Leaves and stem show limited symptoms but roots are damaged and unusable

Cassava Brown Streak Virus (CBSV)

Disease difficult to diagnose early; clear root symptoms appearing late

Transmission through whiteflies and vegetative material

Since 1930’s CBSV known to occur in the lowland and coast of East Africa and Malawi lake

Since 2004, occurrence recorded in higher altitudes of Uganda, Kenya and Tanzania- often with high severities

Increased incidence of CBSV in EA:- introduced CMD-resistant varieties susceptible to the local CBSV strain?

- new CBSV strain?- spreading through infected planting material

Cassava Brown Streak Virus (CBSV)

Distribution of CBSV in Eastern,central and southern Africa in 2008

Cassava virus diseases management in East Africa

through resistant varieties and clean vegetative material

Multiplication and distribution of clean cassava material

•Estimated production area (15 countries): 5,623,500 ha

•Few resistant and suitable varieties to be multiplied and distributed to small scale farmers as soon as possible

•Multiplication of clean material

– Low rate: 8-10 cuttings/plt/yr

– Bulky, perishable sticks (reduced germination through transportation)

– Expensive and logistically difficult

Associated problems:

• Reduced genetic diversity

• Emergence of new virus species or strains

• Level of adaption of new varieties to local conditions

• Inability of farmers to pay for planting material

Options

• Farmers’ early participation in varietal selection

• Enhanced local private sector development –including progressive farmers and farmers groups - for multiplication of cuttings

• Improved farmers’ decision-making capacities in field management

Rice yellow mottle virus (RYMV) symptoms in infected rice field, Ivory Coast (Bouaké, 1995).

Chlorosis, stunting and empty panicles

Virus is spread primarily through mechanical transmission (injuries, people and beetles and.....)

Ref: N. K. Kouassi et al, 2005. Distribution and Characterization of Rice yellow mottle virus: A Threat to African Farmers. Plant Disease, Volume 89, Number 2: 124-133

Rice Yellow Mottle Virus (RYMV) in Africa

Reported in;Burkina Faso, Cameroon, Chad, Cote d'Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Madagascar, Malawi, Mali, Mauritania, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Tanzania, Uganda, Zimbabwe, Zanzibar(CABI, 2010)

Rice Yellow Mottle Virus (RYMV) in Africa

Ref: N. K. Kouassi et al, 2005. Distribution and Characterization of Rice yellow mottle virus: A Threat to African Farmers. Plant Disease, Volume 89, Number 2: 124-133

1. extension of host range from wild plants: introduction of rice cultivation into the center of origin of the virus

2. expansion of geographic range: development of rice cultivation allowed the propagation of the virus throughout SSA: from East to West...

3. increase in the disease incidence through intensification of rice cultivation: short distances, introduction of new susceptible varieties (Indica from Asia), irrigation, continuous cropping and weeds, resulting in the build up of virus and beetle vector populations

Emergence of RYMV in Africa is associated with stages of rice intensification (Fargette et al, 2006):

Managing plant virus epidemics in developing countries

Higher risks of disease epidemics from agricultural intensification in developing countries:

- Low capacities to design and implement appropriate prevention and control measures

- Fragile and diverse ecosystems

- Higher vulnerability of the population to food insecurity

- Weak policy and enabling environment

Dimensions of managing virus diseases in developing countries

Early disease detection before reaching epidemics

• Diagnostic capacities

• Surveillance

• SMS and other cellphone-based networks

Movement of infected material • between countries

• especially in conflict areas

• refugee camps

Costs, risks and logistics of providing significant quantities of healthy planting material of resistant varieties

Important roles of farmers:

– coping strategies under disease conditions

– requirements and preference for varieties

– knowledge and decision-making capacities in field management

– Farmers as observers

– Participatory capacity building approaches (Farmers Field Schools)

Policies that support / disrupt disease management strategies

Information sharing on disease emergence and

Dimensions of managing virus diseases in developing countries

Farmer Scientist

Ms. Elizabeth Ms. Elizabeth

BaratsaBaratsa

of Bungoma, Western Kenya Explains HER concept of Vector Transmission of Maize Streak Virus between plants of a recommended variety to a national researcher from Uganda

Policies that support / disrupt disease management strategies

Awareness and support of policy makers

Information sharing on disease emergence and spread regionally and globally

Dimensions of managing virus diseases in developing countries

• Developing countries are going through the process of crop intensification in order to feed growing populations without new crop land

• They are more vulnerable to the destabilizing impact of plant virus diseases on food security

• Research and technology results will only be valuable when adopted and efficiently scaled-up to reach the most vulnerable farming communities in time

Conclusions

Managing plant virus diseases is more difficult than simply producing a resistant variety: it must deal with changing interactions among the virus pathosystem components -virus, vector, host and environment

Disease management options are often not locally available and may be costly, time and labourconsuming

New scientific methods and IT networks have allowed us to understand the causes of emergence of virus diseases and their interaction with crop intensification.

Virus evolution is rapid and still unpredictable

Conclusions

Thank you