Phinehas Tukamuhabwa

The genetic diversity and population structure of common bean (Phaseolus vulgaris L) germplasm in Uganda

The knowledge and understanding of the genetic variability of common bean ( Phaseolus vulgaris L.) germplasm is important for the implementation of measures addressed to their utilizations and conservation. The objective of this study was to characterize common bean in Uganda using polymorphic molecular markers for use in hybridization and variety development. Genomic DNA was extracted from plants at the first trifoliate leaf stage growing in pots using the modified cetyl-trimethylammonium bromide (CTAB) method. The gene pool membership (Andean vs. Mesoamerican) for each accession was established with the phaseolin marker. Simple sequence repeat (SSR) alleles were separated by capillary electrophoresis that provided further information on the organization of genetic diversity. The Andean and Mesoamerican genotypes were present in similar frequencies (51 vs. 49%, respectively). All SSR markers tested were polymorphic with mean polymorphism information content (PIC) of 0.8. The model-based cluster analysis of SSR diversity in the STRUCTURE software found three sub populations (K3.1, K3.2 and K3.3) genetically differentiated with moderate Wrights fixation indices ( F ST ) values 0.14, 0.12 and 0.09, respectively and many cases of admixture. The STRUCTURE result was confirmed by Principal Coordinate analysis (PCoA) which also clustered beans in three groups. Most Andean genotypes were included in K3.1 and Mesoamerican genotypes belonged to the K3.2 and K3.3 subgroups. This study sets the stage for further analyses for agronomic traits such as yield, resistance to biotic and abiotic stresses and the need for germplasm conservation. Keywords: Phaseolin, Simple sequence repeat (SSR), hybridization, wrights fixation index ( F ST ), structure. African Journal of Biotechnology , Vol 13(29) 2935-2949

Field evaluation of Ugandan sweetpotato germplasm for yield, dry matter and disease resistance

A total of 946 morphologically distinct accessions of sweet-potato (Ipomoea batatas [L.] Lam) germplasm collected from Uganda were evaluated along with four released cultivars for root yield, dry matter, sweetpotato virus disease (SPVD) and Alternaria bataticola blight disease resistance for two seasons; 2005B (September 2005 to January 2006) and 2006A (April to August 2006) at three sites for selection of superior genotypes. The genotypes differed significantly in yield, dry matter content, SPVD and Alternaria blight resistance (p=0.05). Genotype SPVD severity ranged from 1.0 to 5.0 with an overall mean of 2.6. Alternaria severity scores ranged from 1.0 to 5.0 with an overall mean of 2.2. Total root yields ranged from 0.0 to 52.5 t ha−1 with an overall average of 20.3 t ha−1. Most genotypes had mean total root yields of less than 15.0 t ha−1, low specific gravity values of less than 2.0, and low disease resistance. A positive correlation was observed between SPVD and Alternaria blight (r=0.33), while both diseases were negatively correlated with yield traits. A total of 192 superior genotypes were selected for further evaluation and use for variety development in hybridization schemes.

Ureide essay to assess N2-fixation abilities of soybean (Glycine max) genotypes under different Bradyrhizobium strains

The high protein content of soybean (Glycine max) seeds results in high nitrogen demand, causing a huge nitrogen uptake during plant growth. As a legume crop, soybean can fix atmospheric N through symbiotic associations with Bradyrhizobia and perform well in African nitrogen poor soils. This study aimed at establishing the ability of promiscuous soybean genotypes to fix nitrogen and devise the relationship between nodule scores and amount of nitrogen fixed. Twelve soybean genotypes were inoculated with Bradyrhizobium japonicum Strain USDA 110 (specific) and Bradyrhizobium sp. Strain USDA 3456 (native) and raised in pots in a greenhouse. At the R3.5 growth stage, nodules were scored and xylem sap was extracted, which xylem sap was used to carry out ureide, amino-N, and nitrates assays. The relative abundance of ureide was used to devise the proportion of nitrogen fixed by each genotype. The proportion of nitrogen derived from atmospheric N2 (Ndfa) ranged from 47.9 to 78.8% under USDA 3456 and from 36.7 to 78.7% under USDA 110. A strong correlation was found between nodule scores, especially nodules’ effectiveness, and Ndfa. The genotypes Wondersoya (78.8%), Maksoy 2N (78.4%), Namsoy 3 (78.3%), and Maksoy 3N (75.7%) had high nitrogen-fixing ability in response to USDA 3456. Promiscuous soybean genotypes can fix nitrogen equally under both native and specific Bradyrhizobium types. Nodules’ effectiveness can be a good predictor of biological nitrogen fixation. This study highlighted that crop improvement to boost soybean production in Africa should target promiscuous varieties for better yield with less inputs.

Next-Generation Sequencing Reveals the First Complete Genome Sequence of Cowpea aphid-borne mosaic virus from Uganda

ABSTRACT We present here the first complete genome sequence of Cowpea aphid-borne mosaic virus (CABMV) isolated from cowpea in Uganda and compare it with five CABMV complete genome sequences from Brazil (2), India (2), and Zimbabwe (1). It most resembled the genomes of two Brazilian isolates (MG-Avr and BR1) and one Indian isolate (RR3).

Genetic variation, Heritability estimates and GXE effects on yield traits of Mesoamerican common bean (Phaseolus vulgaris L) germplasm in Uganda

Germplasm of common beans from the Mesoamerican gene pool races: Durango, Jalisco, Mesoamerica and Guatemala have highest genetic variation for the crops improvement. The objective was to assign 50 common bean germplasm in Uganda into its gene pool races based on analyses of population structure. Secondly, to estimate heritability and effects of genotype × environment (GXE) interaction on common bean agronomic and yield traits in space and time. Sample genomic DNA was amplified in 2011 with 22 Simple sequence repeat markers (SSRs) and alleles separated using capillary electrophoresis. Field evaluations were conducted in 2010 and 2011 at NaCRRI and 2015 at CIAT – Kawanda. Multivariate analyses of SSRs data identified four subgroups within the germplasm: K4.1–K4.4, with corresponding Wrights fixation indices ( F ST ) as 0.1829 for K4.1, 0.1585 for K4.4, 0.1579 for K4.2 and least for K4.3 at 0.0678. Gene pool race admixtures in the population (14%) were notable and attributed to gene flow. Four superior parents currently used in improving resistance to major diseases grouped as; Jalisco for MLB49-89A; Mesoamerica for MCM5001 and G2333; Durango for MEXICO 54. Heritability values for yield traits estimated using phenotypic data from above fixed parents, was above 0.81. Season and location had significant effect ( P