presentation made for Research purposes

1. DETERMINATION OF PHYTOPLASMA HOST RANGE
AMONG WILD GRASSES IN WESTERN KENYA
PRESENTED BY;
Adam O. Juma
I56/10103/08
(Kenyatta University)
SUPERVISORS;
Dr. Runo S. Maina
Kenyatta University
Dr. Charles A. O. Midega
International Center of Insect Physiology and Ecology.

2. Hypothesis
Background information
a
• 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 b
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.

3. 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
HWLD NSD
BGWL

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

5. 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.

6. Study Area

7. Sampling strategy
1-3m
1-3 m
1m
1m
Transects Quadrat Grass field boundary

8. Collection of leaf
samples (300mg) DNA extraction PCR amplification
CTAB Method (Doyle & P1/P6 Primer pair
Doyle, 1990)
(Saitou & Nei, 1987) nPCR
neighbour joining method
Phylogenetic analysis by NapF/NapR Primer pair
using BLAST search at NCBI
Comparison of sequences
aracterization by
notypic Purification of PCR
quencing of PCR products
oducts
Characterization
Phytoplasma detection &

9. Diversity of grasses in Busia and Bungoma districts
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%

10. 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

11. Incidence of Phytoplasma in Busia and Bungoma
Phytoplasma infection in
common grasses of both
districts.13% of sampled
grasses infected.
11% infected in Busia
Low, widespread
infection in Busia
(between 7 – 22%
infection)
14% infected in Bungoma.
Highest infection in
Cynodon dactylon and
Bracharia (35% and 18.5%
respectively!)

12. Latent infections in Busia and Bungoma
63% of all phytoplasma
infections Latent!
42.9%
79% of infected plants in
27.3% Busia asymptomatic.
25.0%
Bracharia, Cynodon and
other identified grasses.
44.0%
48% of infected plants in
Bungoma asymptomatic.
Cynodon and Digitaria
16.0%

13. 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%)

14. 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

15. Implications
1. 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

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

17. Thank you