PRESENTED BY;

Adam O. JumaI56/10103/08(Kenyatta University)

SUPERVISORS;

Dr. Runo S. MainaKenyatta University

Dr. Charles A. O. MidegaInternational Center of Insect Physiology and Ecology.

DETERMINATION OF PHYTOPLASMA HOST RANGE AMONG WILD GRASSES IN WESTERN KENYA

HypothesisBackground information• Phytoplasma affects many unrelated plants

worldwide

• In East Africa, Napier stunt phytoplasma poses a serious threat to Napier grass farming

• The disease symptoms include severe stunted growth and loss of biomass

• The disease is mainly transmitted by a leafhopper Maeistas (=Recilia) banda in Kenya (Obura et al., 2009)

Photographs illustrating the comparison between Health (a) & Diseased (b) Napier grass.

a

b

Statement of the problem• Napier stunt disease has reduced Napier productivity by 30-90% in

the region

• Phytoplasma attacks other wild grasses, it is likely that several wild grasses could be infected by specific phytoplasma strains

• These wild grasses might also act as reservoirs for fresh inoculums

• The determination of phytoplasma host range among wild grasses is necessary for precise and sustainable phytoplasma disease management

BGWL HWLD NSD

Hypothesis

There is no diversity of wild grasses hosting phytoplasmas in Western Kenya.

Objectives

General Objective• To identify phytoplasmas wild host range among wild

grasses in Western Kenya.

Specific Objectives• To detect and identify phytoplasma strains infecting

wild grasses in western Kenya• To identify wild grass species hosting phytoplasmas in

Western Kenya.

Study Area

Sampling strategy

QuadratTransects1m

1m

Grass field boundary

1-3m

1-3 m

Collection of leaf samples (300mg) DNA extraction

CTAB Method (Doyle & Doyle, 1990)

PCR amplification

P1/P6 Primer pair

nPCR

NapF/NapR Primer pair

Comparison of sequences using BLAST search at NCBI

Phylogenetic analysis by neighbour joining method (Saitou & Nei, 1987)

Purification of PCR products

Characterization by genotypic Sequencing of PCR products

Phytoplasma detection & Characterization

Pennisetum polystachion 1.6%Echinochloa pyramidalis 0.7%Eragrostis curvula 0.7%Hyparrhenia pilgerama 0.7%Sorghum versicolor 0.7%Rottboelia cochinchinensis 0.3%Setaria incrassata 0.3%Sporobolus pyramidalis 0.3%Themeda triada 0.3%

Panicum maximum 0.4%Hyparrhenia pilgerama 1.2%Sporobolus pyramidalis 0.9%Cymbopogon nardus 0.6%Eragrostis curvula 0.6%Setaria incrassata 0.6%Cenchrus ciliaris 0.3%Eleusine indica 0.3%Pennisetum purpureum 0.3%Poverty grass 0.3%

Diversity of grasses in Busia and Bungoma districts

Diversity of grasses in Busia and Bungoma districts

• D. scalarum, C. dactylon and Brachiaria are the most dominant in both districts

• Account for 69% and 76% of the grasses sampled in Busia and Bungoma respectively

Incidence of Phytoplasma in Busia and BungomaPhytoplasma infection in common grasses of both districts.13% of sampled grasses infected.

11% infected in BusiaLow, widespread infection in Busia (between 7 – 22% infection)

14% infected in Bungoma.Highest infection in Cynodon dactylon and Bracharia (35% and 18.5% respectively!)

Latent infections in Busia and Bungoma

63% of all phytoplasma infections Latent!

79% of infected plants in Busia asymptomatic. Bracharia, Cynodon and other identified grasses.

48% of infected plants in Bungoma asymptomatic.Cynodon and Digitaria

27.3%25.0%

42.9%

44.0%

16.0%

Modeled proportions of potential host grasses relative to other grasses (GLM)

Model: Takes into consideration abundance and infection statuses

Bungoma

Bracharia and C. dactylon the main host of phytoplasma in Bungoma

Bracharia 22% (95% CI 10 – 51%; P<0.01) and Cynodon dactylon 53% (95% CI 38 – 76%; P<0.01) of host grasses

Busia

Other (unidentified) grasses account for 28% (95% CI 11 – 71%; P<0.05)

Other notable hosts include Bracharia 12% (95% CI 6 – 25%) and Digitaria 7% (95% CI 4 – 15%)

Inferences• There is great diversity of wild grasses in Busia and

Bungoma districts with Digitaria, Cynodon, Brachiaria grasses being most abundant: (72.5%)

• 63% of all sampled phytoplasma positive grasses had latent infections

• In Bungoma, C. dactylon(22%) and Brachiaria(53%) constitute the main phytoplasma hosts

• In Busia, unidentified grasses(28%) are the main hosts, however, Brachiaria(12%) and Digitaria(7%) are significant phytoplasma hosts

Implications1. Phytoplasma is widespread in many local wild grass

populations in Busia and Bungoma districts

2. Approximately more than half of phytoplasma infections are latent/ assymptomatic

3. Bracharia and C. dactylon are the main host grasses for phytoplasma in Bungoma

4. Host species for phytoplasms in Busia less defined with many species (notably Bracharia and D. sclaranum) as well as other unidentified grasses hosting the pathogen

Acknowledgement

• I.C.I.PE• THE McKNIGHT FOUNDATION• SUPERVISORS• KENYATTA UNIVERSITY

Thank you