Browsing by Author "Kubiriba, J."

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    Banana field resistance to insect-vector transmission of bacterial wilt caused by Xanthomonas campestris p.v musacearum
    (African Journal of Agricultural Research, 2019) Mudonyi, B.; Vanhaelewyn, L.; Tusiime, G.; Ssekiwoko, F.; Kubiriba, J.; Tushemereirwe, W. K.; Changa, C. M.
    Banana, a major staple in East and Central Africa is constrained by banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris pv. musacearum (Xcm). Xcm-infected plants are rapidly destroyed leading to 100% yield loss. Cultural controls are effective but laborious attracting laxity among farmers. This has led to epidemic resurgence in areas where BXW had been contained hence spread to new regions. Reliable control option would be planting Xcm-resistant varieties but extensive germplasm evaluation for their identification has not been conducted. Objective therefore was to determine existence of Xcm-resistance in banana by evaluating major banana cloneset representatives among indigenous cultivars plus introduced foreign Musa accessions. Potted plants were artificially inoculated with 0.5 ml (108CFU) of Xcm suspension. Promising selections from pot trial were later evaluated under natural transmission in field. Field trial plants were infected via insect vectors from spreader plants of highly susceptible cv Kayinja infected by spraying flowers with Xcm. Severity of Xcm-infection was semiquantified using scales 1-5 and 0-5 for pot and field screening trials respectively. This enabled calculation of disease index as a measure of resistance for each genotype. High index implied highly susceptible banana genotype and low index resistant genotype. Findings 44 days after artificial inoculation showed wild banana M. balbisiana had 0.0 disease index thus highly resistant. All other banana genotypes tested under similar conditions had disease index of 100 thus susceptible. In field (insect vector transmission), disease index varied significantly among various genotypes evaluated, some susceptible while others; M. balbisiana, Mbwazirume, M9 and M. Zebrina resistant throughout 360 days of observation. We recommend that heritable traits that confer resistance in M. balbisiana, Mbwazirume, M9 and M. zebrina to Xcm be identified for utilization in genetic modification of farmer preferred bananas. Varieties Mbwazirume and M9 should be promoted for farmer growing to complement cultural controls against BXW.
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    Banana influences on differential expression of hypersensitive response and pathogenicity gene f (hrpf) in Xanthomonas campestris pv. musacearum
    (African Journal of Biotechnology, 2017) Mudonyi, B.; Tusiime, G.; Kubiriba, J.; Tushemereirwe, W. K.; Changa, C. M.
    Banana Xanthomonas wilt is a devastating disease of cultivated banana in East and Central Africa, manifesting as initial leaf wilting, premature fruit ripening and eventual death of all infected plants leading to total yield loss. In order to contribute towards development of effective disease control options, hrpf expression by Xanthomonas campestris pv musacearum (Xcm) during establishment of Xanthomonas wilt infection was determined. To successfully initiate infection, plant pathogenic bacteria deliver effector proteins into host cells using specialized protein transport system such as the Type III secretion system (TTSS). It is a syringe needle-like translocation apparatus essential for delivery of effector proteins into the host cells and hypersensitive response and pathogenicity gene f (hrpf) encodes one of the structural proteins for effector protein delivery. In this study, hrpf expression by Xcm during establishment of Xanthomonas wilt infection was determined in minimal medium amended with extracts from susceptible banana genotypes and banana host plants. Total RNA was isolated from Xcm recovered from inoculated plants and also from minimal medium amended with banana extracts; cDNA synthesised and hrpf amplified by PCR using gene specific primers. Findings showed that Xcm multiplied in susceptible host banana and minimal medium amended with their extracts but not in resistant M. balbisiana and its extract. hrpf gene was thus amplified from cDNA samples of susceptible banana genotypes and their extracts suggesting its expression and involvement in the successful establishment of Xanthomonas wilt disease by Xcm.
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    The banana microbiome: stability and potential health indicators
    (Acta Horticulturae, 2018) Köberl, M.; Dita, M.; Nimusiima, J.; Tumuhairwe, J.B.; Kubiriba, J.; Staver, C.; Berg, G.
    Banana cultivation represents one of the world’s largest monocultures, and Musa spp. belong to the most important global food commodities. Although the plantassociated microbiome has substantial influence on plant growth and health, there is limited knowledge of the banana microbiome and its influencing factors. We studied the impact of i) biogeography, ii) agroforestry, and iii) Fusarium wilt (race 1) infestation on the banana-associated gammaproteobacterial microbiome analyzing ‘Gros Michel’ (AAA genome) grown in Nicaragua and Costa Rica. Additionally, we investigated iv) the microbiome of the East African highland bananas (EAHB, AAA genome) treated with different organic soil amendment combinations of mulch and manure, and v) the microbiome stability of Xanthomonas wilt-resistant transgenic ‘Sukari Ndizi’ (AAB genome) in Uganda. Overall, the gammaproteobacterial banana microbiome was dominated by Pseudomonadales, Enterobacteriales and Xanthomonadales. An extraordinary high diversity of gammaproteobacterial microbiota was observed within the endophytic microenvironments, endorhiza and pseudostem. Enterobacteria were identified as a highly dominant group in aerial plant parts, especially of the pseudostem and leaves. Our studies show that the gammaproteobacterial banana microbiome is influenced by biogeography and banana cultivar. Work also corroborates findings that agroforestry leads to increased plant health via shifts within the microbiome. In this light, a sophisticated design of manipulating plant microbiomes can help us reduce pesticide and fertilizer use. Using gammaproteobacterial health indicators can help preventing Fusarium wilt infestation. Organic management practices lead to increased microbial soil diversity. Further studies based on more holistic population microbiology are necessary to potentially extend this behavior to the entire microbial community. Our risk assessment shows a stable microbiome for Xanthomonas wilt-resistant transgenic bananas with no consequences for non-target rhizobacteria, although additional studies should address the microbiome stability over a longer time frame.
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    The changing spread dynamics of banana Xanthomonas wilt (BXW) in Uganda
    (African Journals Online (AJOL), 2012) Kubiriba, J.; Bagamba, F.; Rockfeller, E.; Tushemereirwe, W.K.
    Banana Xanthomonas wilt still remains a serious threat to banana production in Uganda. Although the desired long term control strategy would have been use of resistance, no sources of resistance have been found. Further the transgenic resistance under development will only be deployed in the long run. In the meantime, cultural control, remains the driver of BXW management strategy in Uganda. This requires continuous effort by the farmers and other stakeholders. It is imperative that disease spread information be continuously updated to sustainably control BXW. The study was conducted to update the status of BXWto inform the continuous refinement of the control strategy of BXW control in across all the epidemics zones in Uganda. BXW incidence increased from about 1% between 2005 and 2006 to about 3.8% in 2010 in the threatened areas. The BXW prevalence increased from below 5 to 34.4% in the same period. Meanwhile, the incidence and prevalence of BXW in the endemic areas reduced to below 10% and about 40%, respectively, from over 50% between 2006 and 2010. The high prevalence of BXW indicates that BXW is widely spread but the low incidence shows that BXW is at initial linear phases of disease epidemic across all zones. There are also a few clusters of infection with infected fields at various phases of the disease progress curve. This suggests that it is no longer feasible to classify Uganda’s banana growing areas in different epidemic zones. Consequently the strategies to control BXW across the zone are similar.