Browsing by Author "Onaga, Geoffrey"

Now showing 1 - 4 of 4
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    Comparison of Response to Nitrogen between Upland NERICAs and ITA (Oryza sativa) Rice Varieties
    (Journal of Agricultural Science, 2012) Onaga, Geoffrey; Asea, Godfrey; Lamo, Jimmy; Kikafunda, Joseph; Bigirwa, George
    Average yields of upland rice are the lowest in Uganda, and most of the productivity gains attributed to improved varieties are related to increased area of production from clearing virgin lands for rice production. In a bid to optimize productivity, we compared the effect of four nitrogen fertilizer treatments: 0, 40, 80 and 120 kgN/ha and two variety types (ITAs (Oryza sativa) and NERICAs (New rice for Africa)) on grain yield and yield parameters in four locations. Combined analysis of variance revealed that nitrogen fertilizer increased mean grain yields from 2116-5200 kg/ha in the NERICAs and 2331-5100 kg/ha in the ITAs. In all the study areas, NERICA 4 and NARIC 2 outperformed NARIC 1 and NERICA 1, and yield trends were consistent over the years suggesting that the two varieties respond better to N fertilizer application. However, the productivity gains are probably related to genetic potential of the varieties rather than the N fertilizer effect, as reflected by the consistent relative performance between 0 N and other N rates. The heavier grains of NARIC 2 and NERICA 4 suggest greater dry matter accumulation before heading, as these varieties have a longer period of vegetative growth. The significant interaction of location x fertilizer and location x variety reveals the need for evaluating the nitrogen-supplying power of soils in the various cropping systems in the country.
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    Magnaporthe oryzae populations in Sub-Saharan Africa are diverse and show signs of local adaptation
    (bioRxiv, 2020) Onaga, Geoffrey; Suktrakul, Worrawit; Wanjiku, Margaret; Quibod, Ian Lorenzo; Domelevo Entfellner, Jean- Baka; Bigirimana, Joseph; Habarugira, George; Murori, Rosemary; Asea, Godfrey; Ismail, Abdelbagi M.; Jantasuriyarat, Chatchawan; Oliva, Ricardo
    Rice blast caused by Magnaporthe oryzae is one of the most economically damaging diseases of rice worldwide. The disease originated in Asia but was detected for the first time in Sub-Saharan Africa (SSA) around 100 years ago. Despite its importance, the evolutionary processes involved in shaping the population structure of M. oryzae in SSA remain unclear. In this study, we investigate the population history of M. oryzae using a combined dataset of 180 genomes. Our results show that SSA populations are more diverse than earlier perceived, and harbor all genetic groups previously reported in Asia. While M. oryzae populations in SSA and Asia draw from the same genetic pools, both are experiencing different evolutionary trajectories resulting from unknown selection pressures or demographic processes. The distribution of rare 32 alleles, measured as Tajima’s D values, show significant differences at the substructure level. Genome-wide analysis indicates potential events of population contraction strongly affecting M. oryzae in SSA. In addition, the distribution and haplotype diversity of effectors might suggest a process of local adaptation to SSA conditions. These findings provide additional clues about the evolutionary history of M. oryzae outside the center of origin and help to build customized disease management strategies.
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    Morphological and Genetic Diversity Analysis of Rice Accessions (Oryza sativa L.) Differing in Iron Toxicity Tolerance
    (Journal of Crop Science and Biotechnology, 2013) Onaga, Geoffrey; Egdane, James; Edema, Richard; Abdelbagi, Ismail
    A major emphasis in breeding for iron toxicity tolerance in rice is to identify differences that are associated with resistance and harness them for genetic improvement. In this study, thirty accessions, including IRRI gene bank accessions, two varieties from Brazil, 8 cultivars from West Africa and 10 cultivars from Uganda were analyzed for sensitivity to iron toxicity, and genetic diversity using morphological and SSR markers. Two genotypes, IR61612-313-16-2-2-1 and Suakoko 8 showed significantly high resistance with an average score of ² 3.5 on 1 - 9 scale. The SRR markers were highly informative and showed mean polymorphism information content (pic) of 0.68. The PIC values revealed that RM10793, RM3412, RM333, RM562, RM13628, RM310, RM5749, and RM154 could be the best markers for genetic diversity estimation of these rice cultivars. Diversity at the gene level showed an average of 4.61 alleles ranging from 2 to 12 per locus. Mean gene diversity (H) value for all SSR loci for the 30 genotypes evaluated was 0.69 but was decreased to 0.53 when analysis was performed on Ugandan accessions. The low genetic diversity found among the Ugandan accessions is the evidence of a narrow genetic base, and such a scenario has a potential vulnerability for resistance break down. A low correlation was detected between the observed molecular and morphological datasets. This means that a combination of morphological traits and SSR analysis would be required when assessing genetic variation under iron toxic conditions, and could be a practical strategy for breeders when planning crosses. A distinction between the resistant and susceptible accessions in both phenotyping and SSR datasets suggests the presence of unique alleles that could be harnessed for improvement of rice against iron toxicity.
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    Reaction of selected rice genotypes with monogenic resistance to the isolate of Magnaporthe Oryzae collected at Namulonge, Uganda
    (Journal of Plant Breeding and Crop Science, 2022) Nakiyaga, Solome; Chiteka, Zwenhamo Albert; Onaga, Geoffrey; Gibson, Paul; Oloka, Bonny; Badji, Arfang; Edema, Richard
    The fungus Magnaporthe oryzae causes rice blast disease leading to substantial yield losses. This study aims at understanding the effectiveness of R-genes to the isolate of M. oryzae from Namulonge in Central Uganda to decide the incorporation of their carrier lines in local gene pyramiding programs. Eighty-three genotypes (73 monogenic resistance lines and 10 local varieties) were evaluated in two different experiments along with two susceptible and one resistant check in the screen house in a 10 × 8 alpha lattice design with two replications, inoculated by spraying, phenotyped at 7, 14 and 21 days after inoculation (DAI), and data on for disease severity, severity percentage, disease incidence, and relative area under disease progression were analyzed using the restricted maximum likelihood (ReML) in Genstat. The tested genotypes were significantly (P<0.001) different for the first, second and across experiments at 7, 14 and 21 DAI for all the measured traits indicating genetic variability among the tested germplasm for rice resistance to blast disease caused by the Namulonge isolate of M. oryzae. Twenty-five out of eighty-three (22.9%) genotypes had consistently low disease severity scores during the two experiments with a range of 0-3. The R genes Pi3, Pi5 (t), Pi7 (t), Pi-b, Pik, Pi54, Pik-m, Pit, Pita, Pita-2, Piz, Piz-4, Piz-5 were considered effective to this particular isolate. The results of this study set the basis of a breeding program for rice resistance to blast disease caused by the Namulonge isolate of M. oryzae through gene pyramiding.