Browsing by Author "Mukasa, Settumba B."

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    Genome-wide association analysis identifies resistance loci for bacterial blight in diverse East African rice germplasm
    (Academic Journals, 2023-07-31) Okello, Moses; Mildred, Ochwo S.; Lamo, Jimmy; Onaga, Geoffrey; Odong, Thomas L.; Tusiime, Geoffrey; Tukamuhabwa, Phinehas; Mukasa, Settumba B.; Wasswa, Peter; Ogwal, Jonathan; Oliva, Ricardo
    Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight disease has been extensively characterized, and loci against different races identified. Many rice cultivars have been developed and utilized to combat the disease, however, due to the rapid evolution of Xoo, several resistances have broken down. The continuous challenge of ever-evolving Xoo and the breakdown of resistance in cultivated rice varieties make it even more important to discover new loci to enable sustainable durable deployment of broad-spectrum resistance genes in elite breeding lines. African germplasm can be exploited as reservoirs of useful genetic variation for bacterial blight (BB) resistance. This study was conducted to identify loci associated with BB resistance and new genetic donors for the breeding program. To identify candidate sources of resistance for advancing breeding, four virulent strains of Xoo (PXO99, MAI1, BAI3, and Xoo3-1) were used to screen 78 East African accessions by genome-wide association studies. The diverse accessions' core genetic base exhibited high resistance to the Xoo strains. 50.63% of the accessions were highly resistant to the Philippines strain PX099, while 20.25% were highly susceptible to the virulent West African strain MAI1. Two novel resistant loci significantly associated hotspots were identified using 1901 SNPs. The two hits were located on chromosome 12 (Xa25) and Chr. 6 (Xa7, Xa27, Xa33). Novel loci were identified that gives a useful basis for more investigation and a wide core genetic pool of high resistance for broad-spectrum resistance for genetic improvement.
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    Pathogenic and genetic diversity of sclerotium rolfsii, the causal agent of southern blight of common bean in Uganda
    (MDPI, 2025-12-26) Erima, Samuel; Nyine, Moses; Ssemakula, Mildred Ochwo; Tusiime, Geoffrey; Akhunov, Eduard; Akhunova, Alina; Yunusbaev, Ural; Adjei, Emmanuel Amponsah; Mukasa, Settumba B.; Otim, Michael Hilary; Odong, Thomas Lapaka; Nkuboye, Allan; Candiru, Agnes; Paparu, Pamela
    Sclerotium rolfsii Sacc. is a soil-borne fungus that causes southern blight on many crops in the tropical and subtropical regions. In 2018, southern blight was reported as the most prevalent bean root rot in Uganda. Earlier studies ascertained the morphological and pathogenic diversity of S. rolfsii, but a limited understanding of its genetic diversity exists. Knowledge of S. rolfsii genetic diversity is a critical resource for pathogen surveillance and developing common bean varieties with durable resistance. A total of 188 S. rolfsii strains from infected common bean plants were collected from seven agro-ecological zones of Uganda in 2013, 2020 and 2021, and characterized morphologically and pathogenically. The genetic diversity of the strains was assessed using single-nucleotide polymorphisms (SNPs) obtained from whole-genome sequencing. The growth rate of the strains ranged between 1.1 and 3.6 cm per day, while the number of sclerotia produced ranged from 0 to 543 per strain. The strains had fluffy, fibrous, and compact colony texture. The strains were pathogenic on common bean and caused disease severity indices ranging from 10.1% to 93.3%. Average polymorphic information content across all chromosomes was 0.27. Population structure analysis identified five genetically distinct clusters. The results of analysis of molecular variance revealed that 54% of the variation was between clusters while 46% of variation was within clusters. Pairwise comparison of Wright’s fixation indices between genetic clusters ranged from 0.31 to 0.78. The findings of this study revealed moderate genetic diversity among S. rolfsii strains, which should be taken into consideration when selecting strains for germplasm screening.