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.
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.
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
HypothesisThere is no diversity of wild grasses hostingphytoplasmas 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.
Diversity of grasses in Busia and Bungoma districts• D. scalarum, C. dactylon and Brachiaria arethe most dominant in both districts• Account for 69% and 76% of the grassessampled in Busia and Bungoma respectively
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!)
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 Digitaria16.0%
Modeled proportions of potential host grasses relative to other grasses (GLM)Model: Takes into consideration abundance and infection statusesBungomaBracharia and C. dactylon the main host of phytoplasma in BungomaBracharia 22% (95% CI 10 – 51%; P<0.01) and Cynodon dactylon 53% (95% CI 38 – 76%;P<0.01) of host grassesBusiaOther (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 districts2. Approximately more than half of phytoplasma infections are latent/ assymptomatic3. Bracharia and C. dactylon are the main host grasses for phytoplasma in Bungoma4. 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