Browsing by Author "Arthur K. Tugume"

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Changing Dynamics in the Spread and Management of Banana Xanthomonas Wilt Disease in Uganda Over Two Decades
(Phytobiomes Journal, 2023-01-17) Jerome Kubiriba; Rockefeller Erima; Arthur K. Tugume; William Tinzaara; Wilberforce K. Tushemereirwe
Banana Xanthomonas wilt (BXW) is a destructive disease caused by Xanthomonas vasicola pv. musacearum (Xvm), a bacterium that indiscriminately infects all banana varieties grown in East and Central Africa (ECA). In this region, BXW was first reported in 2001 in Uganda and was projected to eliminate >90% of Uganda’s banana crops (worth USD4 billion) if not controlled in less than 10 years. Lack of basic information led to application of control approaches that were based on similarity of BXW symptoms to those of Moko disease of banana. However, the approaches were unsuccessful and, in 7 to 9 years, BXW had covered six countries and threatened to wipe out the banana industry in ECA. However, BXW has been tamed to date, mainly due to relentless and systematic deployment of carefully crafted and packaged cultural control practices based on epidemiological information generated within target banana cropping ecosystems. In Uganda, the initial “top-down” communication approaches reached >85% of banana farming communities but did not mobilize the communities enough into action; hence, only 30% impact in controlling BXW was registered. In contrast, participatory approaches mobilized farming communities into action and effectively controlled BXW at field and community levels to near eradication. The approaches effectively controlled BXW in Uganda and, consequently, in eastern Kenya, northern Tanzania, Rwanda, Burundi, and the Democratic Republic of Congo. This article reviews step-wise processes leading to success over the 2 decades and identifies critical research gaps. Deployment of resistant genotypes is urgently needed as a significant addition to the BXW management toolbox to create BXW-free banana cropping systems in ECA.
Early Withering of Enlarged Ovules in Pollinated Fruits of Bananas (Musa spp.) Suggest Abortion after Fertilization
(Horticulturae, 2022-05-10) Allan Waniale; Settumba B. Mukasa; Arthur K. Tugume; Jerome Kubiriba; Wilberforce K. Tushemereirwe; Robooni Tumuhimbise
Sterility in edible bananas is as a result of a long history of anthropogenic-driven selection for sterile genotypes, since seed is not desirable in fruit pulp for human consumption. However, this poses a challenge to conventional genetic improvement by slowing breeding pipelines. In this study, we investigated whether pollen tubes reach all parts of the ovary, the position of fertilized ovule development in fruits, and potential seed set in selected banana genotypes. We selected four cultivars of East African Highland Cooking bananas (EAHBs), a Matooke hybrid ‘222K-1’, improved diploid ‘2905’, and wild bananas ‘Zebrina (G.F.)’ and ‘Calcutta 4’. There was evidence of pollen tubes in the distal, mid and proximal sections of the fruit, irrespective of hand position and genotype. Fertilization, as indicated by an increase in ovule size, happened along the entire length of the fruit but complete development was biased at the distal end in some genotypes. There were some differences in ovule fertilization rates between hands, with distal hands having more ovules and higher ovule fertilization rates. Ovule fertilization happens in bananas but the vast majority aborts, especially at the proximal end of the ovary. Ovule fertilization rates are generally much lower than available ovules.
Endemism and Reemergence Potential of the Ipomovirus Sweet Potato Mild Mottle Virus (Family Potyviridae) in Eastern Africa: Half a Century of Mystery
(Phytobiomes Journal, 2022-11-29) Arthur K. Tugume; Deusdedith R. Mbanzibwa; Titus Alicai; Christopher A. Omongo; M. N. Maruthi
Viruses have the ability to frequently colonize new hosts and ecological niches because of their inherently high genetic and evolutionary plasticity. However, a virus may emerge and remain of no or less economic importance until changes in viral or environmental factors dictate its epidemiological status. An example is sweet potato mild mottle virus (SPMMV), which was first reported in the 1970s on sweetpotato in eastern Africa. SPMMV has remained endemic in the region and poorly understood, yet accounting for 60 to 95% of losses, especially in mixed infections. Unlike other sweetpotato viruses which have global incidences, SPMMV has never been confirmed outside eastern Africa. This implicates the region as its center of origin but does not fully account for SPMMV’s exclusive geographic delimitation to eastern Africa. Despite its importance, several mysteries and research gaps surround SPMMV, which decelerate efforts for effective virus disease management in sweetpotato. The aim of this review is to articulate research gaps, propose pivotal scientific directions, and stimulate knowledge generation for better management of virus diseases in sweetpotato. Vector-mediated transmission of SPMMV remains enigmatic. Here, we postulate testable hypotheses to explain SPMMV transmission. Comparisons between SPMMV and cassava brown streak ipomoviruses demonstrate epidemiological “hallmarks” for monitoring SPMMV. Evolutionary forces on SPMMV coupled with the virus’ broad host range imply a “silent build up” of more fit variants in a changing climate, and this could explode into a worse disease conundrum. These information gaps need urgent filling to ease future management of virus disease emergences in sweetpotato.
Xanthomonas campestris pv. musacearum Bacterial Infection Induces Organ-Specific Callose and Hydrogen Peroxide Production in Banana
(Phyto Frontiers, 2022-01-03) Abubakar Sadik Mustafa; Benison Tugume; Jamilu E. Ssenku; Paul Ssemanda; Shahasi Y. Athman; Hannington Oryem-Origa; Jerome Kubiriba; Savithramma P. Dinesh-Kumar; Arthur K. Tugume
Xanthomonas campestris pv. musacearum (Xcm) bacteria cause banana Xanthomonas wilt (BXW), the most destructive disease of bananas in East and Central Africa. During early stages of infection in susceptible banana cultivars, incomplete systemic movement of Xcm limits bacterial colonization in the up- per organs. The mechanistic basis of this delayed movement is unknown. We hypothesized that Xcm infection triggers basal pattern-triggered immune (PTI) responses whose spatial and temporal variability along the banana’s anatomical structure accounts for initially limiting Xcm in upper organs. Hence, we examined PTI responses such as callose deposition and hydrogen peroxide (H2O2) production in different organs in response to Xcm infection in BXW-susceptible Kayinja and Mbwazirume banana cultivars and wild resistant progenitor Musa balbisiana. Xcm-induced callose increased and peaked at 14 days postinoculation (dpi) and 28 dpi as assessed by fluorescence microscopy and enzyme-linked immunosorbent assays, respectively. The levels of Xcm-induced H2 O2 and callose were highest in the pseudostems and corms, respectively, and were independent of host susceptibility or resistance to BXW. H2O2 production showed a biphasic transient pattern with an initial increase at 1-hour post Xcm inoculation (hpi), followed by a decline 3 to 6 hpi and then a second increase by 12 hpi. Our findings point to organ-specific responses to Xcm infection in bananas. The corm, which doubles as a subterranean perennating organ and interface between mother plants and lateral shoots, was the most responsive organ in callose production, whereas the pseudostem was the most responsive organ in H2O2 production, suggesting the significance of these organs in banana response to BXW.