The genetic relationships among 192 superior, high–yielding, and disease-resistant sweetpotato [Ipomoea batatas (L.) Lam] accessions from the Ugandan germplasm collection were analyzed using 10 fluorescent labeled simple sequence repeat (SSR) markers. Relatedness among the genotypes was estimated using the Nei and Li genetic distance coefficient, cluster analysis and principle component analysis methods of NTSYS-pc software. The polymorphic information content of the SSR markers used in this study ranged from 0.23 to 0.76 for loci IB-S07 and IB-R12, respectively, with a mean value of 0.62. The number of polymorphic alleles detected per locus ranged from two to six with a mean of four, a confirmation of the effectiveness of microsatellite detection on an automated ABI 3730 sequencer. The mean pairwise genetic distance among the 192 genotypes was 0.57, an indication of moderately high genetic diversity. Cluster analysis divided the accessions into four major groups with no relationship to the district of origin. Two sets of duplicates were identified through SSR genotyping in this study. Up to 190 distinct accessions for use as potential parental genotypes in hybridization schemes for cultivar development in the region were identified.

Studies were conducted to quantify the yield loss attributable to soya bean rust, a relatively new disease in Uganda. This was carried out for three consecutive seasons in the central, eastern, northern and western parts of the country, using three commercial varieties (Nam 1, Nam 2 and Namsoy 3) and two elite varieties (UG‐5 and GC‐00138‐29). The commercial varieties recorded higher yield losses (26.9–36.3%) and higher rust severities >50%, whereas the elite varieties recorded lesser yield losses of <10% and rust severities of <30%. Yield losses were highest in the central region (22.9%), and lowest in the northern region (15.1%). Yield losses differed significantly between seasons and were associated with reduction in seed weight and filled pod per plant.

Soybean is a major source of oil and proteins worldwide. The demand for soybean has increased in Africa, driven by the growing feed industry for poultry, aquaculture and home consumption in the form of processed milk, baked beans and for blending with maize and wheat flour. Soybean, in addition to being a major source of cooking oil, is also used in other industrial processes such as in the production of paints and candle wax. The demand for soybean in Africa so far outweighs the supply, hence the deficit is mainly covered through imports of soybean products such as soybean meal. The area under soybean production has increased in response to the growing demand, a trend that is expected to continue in the coming years. As the production area increases, diseases and insect pests, declining soil fertility and other abiotic factors pose a major challenge. Soybean rust disease, caused by the fungus Phakopsora pachyrhizi, presents one of the major threats to soybean production in Africa due to its rapid spread as a result of the ease by which its spores are dispersed by the wind. Disease control by introducing resistant soybean varieties has been difficult due to the presence of different populations of the fungus that vary in pathogenicity, virulence and genetic composition. Improved understanding of the dynamics of rust ecology, epidemiology and population genetics will enhance the effectiveness of targeted interventions that, in turn, will safeguard soybean productivity.

Sweetpotato [Ipomoea batatas (L.) Lam] is a widely grown and consumed root crop in Uganda. A total of 1303 accessions of sweetpotato germplasm collected from 21 districts of Uganda were planted for morphological characterization. Forty morphological descriptors were scored on 1256 accessions 90 to 100 d after planting. Stepwise discriminant analysis showed that the discriminating power of 20 morphological traits was sufficient to differentiate the accessions. The level of morphological variation for the 40 traits estimated using the Shannon Weaver diversity index (H') ranged from 0.10 to 0.99, with an overall mean of 0.71 ±0.03, suggesting a highly diverse collection. Cluster analysis using the unweighted pair‐group method using arithmetic averages grouped the 1256 accessions into 20 major clusters, with the number of accessions per cluster ranging from 15 to 166. The general leaf outline was highly correlated with leaf lobe type (r = 0.79) and leaf lobe number (r = 0.80) and were the predominant characters in grouping the accessions to clusters. No grouping of accessions based on region of origin was observed, suggesting movement of germplasm between regions. Approximately 70% of the accessions were morphologically distinct and a collection of 946 accessions was selected to represent Ugandan sweetpotato landrace diversity. The complete passport data for this collection is available at: http://www.viazivitamu.org/ugasp_db/gis.htm

Host plant resistance is the best long-term strategy for managing soybean rust (Phakopsora pachyrhizi) in endemic areas. Resistance breeding efforts are hampered by the presence of several races of the pathogen that often overcome single resistance genes deployed against them. In Uganda, only two soybean cultivars show moderate resistance to Phakopsora pachyrhizi, but this is likely to break down given the aggressive nature of the pathogen. A total of 25 rust tolerant or resistant accessions were imported from the Asian Vegetable Research and Development Centre and screened at Namulonge, in central Uganda. Only 10 accessions, G 33, G 8527, G8586, G 8587, GC 60020-8-7-7-18, GC 87016-11-B-2, GC 87021-26-B-1, SRE-D-14A, SRE-D-14B, and SS 86045-23-2, showed no rust symptoms at growth stage R6 during the three seasons of testing. Soybean rust resistance genes Rpp1, Rpp3, and Rpp4 did not confer resistance at Namulonge; gene Rpp2 was effective.

Cassava brown streak disease (CBSD) is the most devastating disease of cassava in southern, eastern and cntral Africa, and can cause up to 100% yield loss. Limited progress has been made in breeding for host plant resistance due to limited knowledge on the resistance variability to the disease. Reaction of promising cassava genotypes to CBSD in multi-environments are also unknown. Therefore, this study intended to: (1) Identify additional sources of resistance to CBSD; (2) Determine the stability of resistance to CBSD, and (3) mega-environments for screening resistance to CBSD. Field evaluation of 19 genotypes was conducted in RCBD with three replications at three agro-ecologies of Uganda for two cropping cycles. Additive Main Effects and Multiplicative Interaction (AMMI) and (GGE) biplot models were used to analyze genotype-environment interactions. Based on mean field reaction, the six best genotypes identified for resistance to CBSD were: TZ/06/140, TMS30572, TZ /06/130, N3/66/1, N3/58/1 with N3/104/3 and N3/66/1 being the most stable. While N3/66/1, N3/58/1 and N3/104/3, Mzungu and Kigoma Red were reported to be putative new sources of resistance to CBSD in Uganda. Genotypes (G), Environments (E), and GxE interactions were all significant, with no genotype exhibiting complete resistance. The significant result for GxE interaction to CBSD indicates the need for multi-environment screening and is suggestive of quantitative nature of CBSD resistance.

A major impediment to breeding for resistance to Asian soybean rust (Phakopsora pachyrhizi) is the lack of stable sources of resistance, due to high variability in the pathogen. The objectives of this study were to assess comparative virulence of five diverse field isolates from major soybean producing areas in Uganda, and identify lines with resistance to isolates of soybean rust in seedling and adult plants under screen house and field conditions respectively. When inoculated with the five field isolates, all twelve lines evaluated showed diverse and mixed reactions, suggesting each location differed in soybean rust races and/or virulence. Experimental sites growing many diverse soybean lines yearly had the greatest diversity of soybean rust. The effectiveness of specific resistance genes was restricted to certain locations and gene Rpp2 previously resistant was ineffective producing a susceptible tan reaction at the seedling stage. A positive correlation between mean lesion density at the seedling stage and adult plant severity indicated that using field isolates to screen for seedling resistance can be a useful breeding approach to extrapolate resistance in adult plants. Overall, these results emphasise the relevance of using field isolates from the target areas to evaluate lines for soybean rust resistance.

Yam bean (Pachyrhizus spp.) is legume crop that not only produces edible roots but also has a high yield of unutilized seeds. Although the yam bean seeds are rich in protein, they are not used due to a high content of toxic rotenone. In this study, yam bean seeds were detoxified and the nutritional and functional properties of their protein determined to assess the proteins' potential for applications. Seeds of 10 accessions (2 accessions of P. erosus, 4 accessions of P. ahipa and 4 accessions of P. tuberosus) were analyzed for proximate composition, pasting and functional properties (bulk density, least gelation concentration, water absorption capacity, oil absorption capacity, emulsifying capacity, emulsion stability, foaming capacity, foam stability and protein solubility). The results showed that yam bean seeds contained: 29.2-32.1 g/100g proteins, 31.3-33.0 g/100 g carbohydrates, 24.1-25.6 g/100g total fat, 7.5-8.1 g/100g crude fiber and 3.4-4.1 g/100g ash. The defatted P. erosus seed flour contained 45.6-48.8 g/100g protein, 32.6-36.5 g/100g total carbohydrate, 6.7-7.1 g/100g crude fiber, 6.0-6.4 g/100g ash and 5.2/100 g crude fat. The defatted yam bean seed flour exhibited relatively high protein solubility (68.0%-70.4%), least gelation concentration (14%), water absorption capacity (2.8%-2.9%) and oil absorption capacity (1.5%). The defatted flour exhibited emulsifying capacity of 35.7%-36.0%, emulsion stability of 33.2%-33.5%, foaming capacities of 42% and foam stability of 25.1%-25.8%. With respect to pasting properties, the defatted yam bean seed flours exhibited pasting temperature of 80.0˚C-81.3˚C, peak viscosity of 145.5-146.7 RVU, trough viscosity of 95.1-102.0 RVU, break down of 43.5-51.6 RVU, set back of 252.9-258.1 RVU and final viscosity of 348-360 RVU. The results show that yam bean seed has potential for use in both food and nonfood applications.