DEVELOPING MANAGEMENT STRATEGIES FOR NAPIER STUNT DISEASE

Presented at the ASARECA/ILRI Workshop on Mitigating the Impact of Napier Grass Smut and Stunt Diseases, Addis Ababa,

June 2-3, 2010

Zeyaur R. Khan and Charles A. O. MidegaInternational Centre of Insect Physiology and

Ecology (ICIPE), Nairobi, Kenya

Napier Stunt Disease (NSD) is caused by a phytoplasma (16SrXI) and is transmitted by a leafhopper, Maiestas (Recilia) banda.

The disease is spread by the leafhopper as well as through distribution of infected Napier cuttings.

There may be other grasses in the field which are refugia for the leafhopper and phytoplasma and may contribute to the spread of the disease.

For developing a robust management strategy, we need to fully understand the biology of the disease and its vector.

UNDERSTANDING THE DISEASE AND ITS VECTOR • How is the epidemiology of the NSD?• Are there other vector(s) of the NSD?• What is the distribution of the vector(s)?• What percent of the vector(s) carry phytoplasma?• What are the contributions of vectors in spread of

Napier stunt disease? How about the human factors?

• What is the origin of the vector? How did it come to Napier grass?

• Which other plants are infected now and which could be infected in future?

• What is the distribution of these inoculum sources?

Can Resistant Varieties be Used in Managing Napier Stunt Disease?

• Are resistant varieties available?• Will farmers accept to grow the varieties?• Is resistance stable, durable?• What is the cause of resistance: resistance to

vector or to phytoplasma? • What is the mechanism of resistance: antibiosis,

non-preference/avoidance, tolerance?• Is resistance of high level or moderate level?• Are there biotypes of vectors/ phytoplasma which

could break down resistance in future?• If the resistant variety has high level of resistance

to vector, where will the vector move in future?

STUNT RESISTANT NAPIER?

If Resistant Varieties not Available or not Suitable?

• Are there other grasses which could replace Napier grass as fodder?

• Will farmers accept those grasses to replace Napier?

• Can the vector survive on those grasses?

• Can the vector transmit phytoplasma on those grasses?

• If those grasses are highly resistant to vector, where will the vector move in future? Food crops?

Bracharia sp. cv. Mulato

Cultural control

• Are there other grasses in farmers’ fields which could be refugia for vector and phytoplasma?

• How can we identify those grasses?• Do the vectors move between Napier grass and

refugia grasses?• What is the contribution of those grasses in

spread of Napier stunt disease?• Is the same vector which transmits Napier

phytoplasma also transmits phytoplasma on refugia grasses?

• Can removal of those refugia grasses reduce phyoplasma infection on Napier grass?

Star grass infected with the same phytoplasma which infects Napier grass

Obura et al. 2010. New Disease Reports

Could phytoplasma become a threat to cereal crops?

• Can the vector feed, survive and multiply on cereal crops-such as maize, rice, sorghum, millet, sugarcane, etc?

• If yes, can the vector transmit phytoplasma from Napier to cereal crops?

• If yes, can the phytoplasma affect productivity of cereal crops?

• If vector-resistant varieties are used for phytoplasma control, can the vector move to cereal crops and can phytoplasma then become a threat to cereal production?

Sugarcane Rice Pearl MilletFinger Millet

CAN PHYTOPLASMA AFFECT FOOD CROPS?

Electrophoresis of Phytoplasma DNA in food crops

A

M 1 2 3 4 5 M 1 2 3 4 5

M 1 2 3 4 5M 1 2 3 4 5

Rice Finger Millet

Sugarcane Pearl Millet

PHYTOPLASMA CAN INFECT FOOD CROPS

Contact author for results

WHAT IS THE MINIMUM NEEDED TO DEVELOP

STRATEGIES FOR MANAGEMMENT OF

NAPIER STUNT DISEASE?

FACILITIES TO MAINTAIN CULTURE OF INSECT VECTOR NEEDED

A REGULAR SUPPLY OF NSECT VECTOR NEEDED

MAINTAINING OF DISEASED NAPIER PLANTS WITH ACCESSION NUMBERS

NEEDED

CONTAINMENT FACILITIES FOR MAINTAINING PHYTOPLASMA-FREE NAPIER GRASS

VARIETIES AND GRASSES ARE NEEDED

ROBUST DISEASE SCREENING TECHNIQUES ARE NEEDED

PHYTOPLASMA FREE CULTURE OF VECTOR IS NEEDED TO DO BACK

TRANSMISSION STUDIES

TRACKING THE MOVEMENT OF INSECT VECTOR ON REGULAR BASIS IS NEEDED

PCR AND LAMP FACILITIES TO DETECT PHYTOPLASMA IN PLANTS AND INSECTS ARE

NEEDED

ICIPE’s PROPOSED MANAGEMENT STRATEGIES FOR NAPIER STUNT

• Work closely with National Programmes

• Identify Napier Varieties with Moderate Level of Resistance to Insect Vector but with high level of durable and stable resistance to Phytoplasma.

• Identify other fodder grasses not affected by phytoplasma

• Survey farmers’ perception about resistant Napier varieties and fodder grasses selected

• Survey and record natural hosts for insect vector and phytoplasma in farmers’ fields and study their effects on spread of Napier stunt disease for management

• Avoid using high level of resistance to insect vector