National Crops Resources Research Institute Research Articles

Effects of Selected Crops on Germination and Growth of Bidens pilosa and other Weeds

A screen house pot study was done at Uganda National Crops Resources Research Institute, Namulonge in Uganda during September-December 2021. Profiled metabolites from 5-donor plants; Mucuna pruriens, L. (Mc), Cymbopogon nardus L. (C), Desmodium uncinatum Jacq. DC. (D), (Zea mays, L. (Mz) and New Rice for Africa 1 (NERICA 1) were Terpenoids and Phenols. NERICA 1 (R) is a cross of Oryza sativa and Oryza glaberrima. C produced 10 terpenoids + 1 ester, R and D each released 6 Terpenoids + 3 Phenols. Mc produced 2 Terpenoids + 4 Phenols and 5 Terpenoids + 4 Phenols were profiled from Mz. Completely randomised block design were adopted with 3 replicates and eight combinations of 3 leaf+stem+root powders namely; Mc+D+C, Mz+Mc+C, RDC, Mc+D+C, Mz+R+Mc, Mz+D+Mc, R+Mc+C and Mz+R+C, mixed with 1.5 kg soil (15, 30 and 45 %, w/w). Controls had no powders. Mixtures were placed in plastic pots and 20 seeds of Biden pilosa L. were sown in each pot. Every 2 days, 200 ml of water was applied to all treatments for 60 days. Mz+Mc controlled B. pilosa and volunteer weeds relative to R+C and C+D. Weed germination and biomass reduced with increased powder doses. Volunteer monocot weeds were more inhibited than dicots. High potential exists for functional allelopathy using allelochemicals in the donor plants to develop bio-herbicides.

Genetic dissection of cassava brown streak disease in a genomic selection population.

Cassava brown streak disease (CBSD) is a major threat to food security in East and central Africa. Breeding for resistance against CBSD is the most economical and sustainable way of addressing this challenge. This study seeks to assess the (1) performance of CBSD incidence and severity; (2) identify genomic regions associated with CBSD traits and (3) candidate genes in the regions of interest, in the Cycle 2 population of the National Crops Resources Research Institute. A total of 302 diverse clones were screened, revealing that CBSD incidence across growing seasons was 44%. Severity scores for both foliar and root symptoms ranged from 1.28 to 1.99 and 1.75 to 2.28, respectively across seasons. Broad sense heritability ranged from low to high (0.15 - 0.96), while narrow sense heritability ranged from low to moderate (0.03 - 0.61). Five QTLs, explaining approximately 19% phenotypic variation were identified for CBSD severity at 3 months after planting on chromosomes 1, 13, and 18 in the univariate GWAS analysis. Multivariate GWAS analysis identified 17 QTLs that were consistent with the univariate analysis including additional QTLs on chromosome 6. Seventy-seven genes were identified in these regions with functions such as catalytic activity, ATP-dependent activity, binding, response to stimulus, translation regulator activity, transporter activity among others. These results suggest variation in virulence in the C2 population, largely due to genetics and annotated genes in these QTLs regions may play critical roles in virus initiation and replication, thus increasing susceptibility to CBSD.

Morphological Characterization and Diversity of Bambara Groundnuts in Uganda

Sixty nine Bambara groundnut accessions were evaluated at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda to determine their morphological variability in a randomized complete block design with three replications. Analysis of variance showed significant (P < 0.01) divergence among accessions for all traits. Cluster analysis exhibited six distinct clusters with the highest intra-cluster distance (8.09) observed in cluster II and the lowest distance (0.00) in cluster VI. Maximum inter-cluster distance was observed between cluster VI and IV and minimum distance between cluster II and IV. Inter-cluster distance was much higher than intra-cluster distance suggesting a wider variability among accessions. All late maturing accessions with high yield were grouped in cluster V while early maturing accessions were grouped in cluster III. Results of principal component analysis indicated that both yield and vegetative traits were the principal discriminatory characteristics. The accessions evaluated exhibited high diversity for most traits indicating that they can be used in breeding programs to develop varieties with desirable traits.

Effect of Potassium Nitrate Spray on the Flowering and Fruiting of Mango Varieties Grown in Uganda

Aims: To evaluate the effect of potassium nitrate (KNO3) on flowering and fruiting of mangoes in Uganda.
 Study Design: Randomized complete block design in a split plot arrangement.
 Place and Duration of Study: National Crops Resources Research Institute Namulonge, National Semi–Arid Resources Research Institute in Serere and Bulindi Zonal Agricultural Research and Development Institute in Hoima in 2015 and 2016.
 Methodology: The study was superimposed on eight-year-old mango orchards which were simultaneously planted at the three sites. Main plot treatments comprised three mango varieties (Bire, Tommy Atkins, Zillate), while sub-plot treatments comprised four concentrations of KNO3 (zero as control, 1, 2 and 4%). Data was collected on number of terminal buds induced after applying KNO3, percentage flowering, number of fruits set per 20 panicles and fruit yield per tree.
 Results: Trees sprayed with KNO3 produced higher (P < .05) numbers of terminal buds than the control. Across sites, Bire produced higher numbers of buds (64.8) than Tommy Atkins (46.3) and Zillate (17.8). Flowering response was higher in Bire (28.6%) than in Tommy Atkins (20.8%) and Zillate (17.8%). Flowering response of trees sprayed with 2% KNO3 (31.4%) was higher than that of trees sprayed with 1% KNO3 (24.7%). Mean number of fruits induced per 20 panicles in trees sprayed with 4% KNO3 (8.24) was higher than that of trees sprayed with 1% KNO3 (4.8). Fruit yield of Tommy Atkins (23.01 kg/tree) was higher than that of Bire (10.97 kg/tree). Mean fruit yield of trees sprayed with 2% KNO3 (27.36 kg/tree) was higher than that of trees sprayed with 1% KNO3 (15.93 kg/tree).
 Conclusion: For better fruit yields, farmers at Bulindi should grow Tommy Atkins and apply 2% KNO3. Farmers at Namulonge can grow any of the three mango varieties and apply 2 or 4% KNO3, while those at Serere can grow Tommy Atkins and Zillate, and should apply 4% KNO3.

A population based expression atlas provides insights into disease resistance and other physiological traits in cassava (Manihot esculenta Crantz)

Cassava, a food security crop in Africa, is grown throughout the tropics and subtropics. Although cassava can provide high productivity in suboptimal conditions, the yield in Africa is substantially lower than in other geographies. The yield gap is attributable to many challenges faced by cassava in Africa, including susceptibility to diseases and poor soil conditions. In this study, we carried out 3’RNA sequencing on 150 accessions from the National Crops Resources Research Institute, Uganda for 5 tissue types, providing population-based transcriptomics resources to the research community in a web-based queryable cassava expression atlas. Differential expression and weighted gene co-expression network analysis were performed to detect 8820 significantly differentially expressed genes (DEGs), revealing similarity in expression patterns between tissue types and the clustering of detected DEGs into 18 gene modules. As a confirmation of data quality, differential expression and pathway analysis targeting cassava mosaic disease (CMD) identified 27 genes observed in the plant–pathogen interaction pathway, several previously identified CMD resistance genes, and two peroxidase family proteins different from the CMD2 gene. Present research work represents a novel resource towards understanding complex traits at expression and molecular levels for the development of resistant and high-yielding cassava varieties, as exemplified with CMD.

Allelopathic Potential of Compounds in Selected Crops

Allelochemicals cause yield differences under various ecosystems worldwide. Studies were conducted at the National Crops Resources Research Institute, Namulonge, Uganda during 2016 to investigate allelopathic properties of bioactive compounds in upland rice (NERICA 1), Desmodium uncinatum, Zea mays (LONGE 6H) and Mucuna pruriens root leachates. Studies involved pot screening, equal compartment agar experiments, germination tests and growth of potted plants. Results under the pot study indicated that maize, rice and mucuna leachates significantly (P ≤ 0.05), reduced root lengths (49%-63%), plant heights (48%-66%) and biomass (63%-75%) for Ageratum conyzoides, Bidens pilosa and Gallinsoga. parviflora weeds. G. parviflora root growth was reduced (20%-41%) and stem growth declined (19%-42%) when maize, rice and mucuna leachates were applied in the equal compartment agar study. Increased leachate concentrations (25%-75%) significantly (P ≤ 0.05), increased the mean germination time (0.4-2.8 days) for mucuna, desmodium, rice and maize as seed germination indices (SGI) were reduced (1.3%-49%). Potted mucuna, maize and desmodium reduced (1.3%-49%) rice root length. Potting mucuna with maize reduced (32%) mucuna leaf width while desmodium growth parameters were reduced (49%-64%) when potted with maize and mucuna. Potting maize with mucuna or desmodium increased the maize leaf length (18%) and SGI (25). Application of higher (25%-75%) rice/maize leachate concentrations similarly increased the maize leaf length (31%) and SGI (119). Allelopathic properties affect seed germination, crop growth and development, and characterise ecosystems age structures. Strategic management of crops under allelopathic ecosystems is critical.

Production Potential of Allelopathic Rice, Cymbopogon, Desmodium, Mucuna and Maize

Allelochemicals regulate the productivity of crop ecosystems. A screen house experiment was conducted (2016) at the National Crops Resources Research Institute, Namulonge, Uganda to determine the effects of NERICA 1 rice (an interspecific hybrid between Oryza sativa and O. glaberrima species), Cymbopogon nardus (C), Desmodium uncinatum (D), Mucuna pruriens (Mc) and LONGE 6H, Zea mays (Mz) on crop relative growth rates (RGR), nitrogen (N), phosphorus (P) and potassium (K) nutrient levels. One field study was conducted on a farm (2017) to establish the allelopathic interactive effects of RCDMcMz on Striga hermonthica (a parasitic weed), crop competition and productivity. Data was collected on striga, RMz growth, nutrient levels and yield. Potted rice reduced (30%-47%) in root length but Mz leaf length increased (31% & 15%) with Mc & D. RMc reduced (73%) striga and increased rice RGR (14-42 days). RD similarly reduced (67%) striga. RC increased (96%, 44% & 73%) rice NPK uptake, RGR (14-42 days), reduced (57%) striga and increased (1.56) the combined land equivalent ratio (CLER) and rice grain yields. RMz reduced (16%, 38% & 38%) rice NPK reserves, RGR (14-42 days), CLER (1.0), grain yields and increased (36%) striga. RD recorded higher CLER (1.56). MzMc reduced (15% & 27%) maize P uptake and NP uptake increased (42% & 9.3%) under MzC & MzD (73% & 29%). RMc increased rice RGR (14-42 days). Maize RGR (14-28 days) increased under MzD, MzMc & MzC and reduced (28-42 days) under MzD, RC & MzMc.. The ecosystems’ productivity was attributed to allelopathy.

English

A study was conducted to determine the mode of inheritance for grain shape and aroma traits of lines in the Uganda rice germplasm. Five aromatic and four non-aromatic rice lines were crossed in screen house using North Carolina Design II at the National Crops Resources Research Institute, Uganda. The resulting F2 seeds and their parents were planted in the field using complete randomized block design in two replications. The grain shape and aroma intensity of the harvested F3 seeds on per hill basis were determined in laboratory using instrumental and sensory evaluation procedures, respectively. The results revealed that the inheritance of grain shape and aroma traits were influenced by both additive and non-additive gene actions, but with the grain shape being dominated by additive gene action and the aroma by non-additive gene action. In addition, Supa 3, Supa 5 and Supa 1052 rice lines exhibited good general combining ability effects for the shape trait while Supa 3 and MET 13 were good general combiners for the aroma trait. The superior cross combination from Supa 3 x Supa 5 for grain shape and Supa 3 x MET 13 for aroma trait could be used for selection of the relevant traits at advanced stages of the breeding cycles. Key words: General combining ability effects, gene action, North Carolina design II, selection, sensory evaluation.

Effective isolation distance for prevention of cassava virus infections in Uganda

Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are the major viral diseases of cassava in Uganda. Although isolation distance of “50 m” has been recommended by MAAIF in Uganda for prevention of virus infections in crops, the minimum isolation distance has not been verified for effectiveness in cassava. This study assessed the effective isolation distance for management of viral diseases in cassava. Virus-clean cassava cultivars (NASE 03, NASE 14 and NAROCASS 1) from farmers’ fields were used as field sourced (FS) planting materials. Tissue culture (TC) material of the same cultivars were sourced from the National Crops Resources Research Institute and Makerere University Agricultural Research Institute tissue culture laboratories. Both FS and TC materials were tested at isolation distances of 50, 100, 150 and 250 m for virus prevention. The experiment was laid out in a randomised complete block design and was run for 12 months after planting (MAP). Mean CBSD/CMD prevalence significantly varied (P<0.05) among isolation distances in both FS and TC plants, and the 250 m isolation distance was the most effective in reducing disease prevalence. Across cultivars and planting material category at 12 MAP, the 50 m isolation distance had the highest foliar incidence for CBSD (29.2%) and CMD (16.1%); while severity for CBSD was 1.4 and 1.2 for CMD. At 250 m, all FS and TC plants had CBSD/CMD severity of 1.0 and 0% incidence. These results show that 250 m isolation distance can provide an option to disseminate popular, but CBSD/CMD susceptible cassava cultivars thereby manage CBSD/CMD.

Effective isolation distance for prevention of cassava virus infections in Uganda

Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are the major viral diseases of cassava in Uganda. Although isolation distance of “50 m” has been recommended by MAAIF in Uganda for prevention of virus infections in crops, the minimum isolation distance has not been verified for effectiveness in cassava. This study assessed the effective isolation distance for management of viral diseases in cassava. Virus-clean cassava cultivars (NASE 03, NASE 14 and NAROCASS 1) from farmers’ fields were used as field sourced (FS) planting materials. Tissue culture (TC) material of the same cultivars were sourced from the National Crops Resources Research Institute and Makerere University Agricultural Research Institute tissue culture laboratories. Both FS and TC materials were tested at isolation distances of 50, 100, 150 and 250 m for virus prevention. The experiment was laid out in a randomised complete block design and was run for 12 months after planting (MAP). Mean CBSD/CMD prevalence significantly varied (P&lt;0.05) among isolation distances in both FS and TC plants, and the 250 m isolation distance was the most effective in reducing disease prevalence. Across cultivars and planting material category at 12 MAP, the 50 m isolation distance had the highest foliar incidence for CBSD (29.2%) and CMD (16.1%); while severity for CBSD was 1.4 and 1.2 for CMD. At 250 m, all FS and TC plants had CBSD/CMD severity of 1.0 and 0% incidence. These results show that 250 m isolation distance can provide an option to disseminate popular, but CBSD/CMD susceptible cassava cultivars thereby manage CBSD/CMD.&#x0D;

Allelic variations in aroma gene in cultivated rice varieties

Germplasm is a valuable source of genetic diversity that supports crop improvement efforts in any breeding programme but it must first be fully characterised for economically valuable traits before it can be effectively utilised. In rice (Oryza sativa), the development of new varieties with improved aroma requires correct phenotyping and prior knowledge of the available genes and alleles governing the aroma trait in the gene pool. Correct phenotyping and genotyping can be achieved using sensory methods and functional markers associated with polymorphisms that define the aroma genes. The objective of this study was to evaluate the aroma status of rice accessions and to assess for the various alleles of badh2 gene using functional markers. A total of 56 rice accessions were evaluated at National Crops Resources Research Institute (NaCRRI) in Uganda for their aroma using sensory methods and a molecular marker to differentiate between aromatic and non- aromatic accessions. The aromatic accessions were then evaluated for variations within the betaine aldehyde dehydrogenase2 (badh2) gene responsible for aroma in rice using functional markers. Sensory evaluation of aroma identified 23 accessions to be aromatic; while 33 were non-aromatic. Molecular results identified 20 accessions as aromatic; while 36 accessions were non-aromatic. Functional marker analysis indicated the presence of badh2-E7 allele in 20 aromatic accessions within this collection that could be employed in the breeding programme for the rice aromatic trait.&#x0D; Key words: badh2 alleles, functional markers, Oryza sativa

Volatile Organic Compound Based Markers for the Aroma Trait of Rice Grain

A study was conducted to determine the volatile organic compounds (VOCs) associated with rice grain aroma in 37 commonly grown lines within Uganda, as well as elites. The aim of the study was to identify potential volatile biochemical markers, if any, for the rice grain aroma trait. Certified rice seeds were obtained from the Uganda National Crops Resources Research Institute germplasm collection. The seeds were sown into experimental plots, under field conditions and the mature paddy harvested. Polished rice grains were heated to 80 oC and the liberated VOCs subjected to untargeted metabolite analysis using gas chromatography-time-of-flight mass spectrometry. In total, nine functional groups were present; hydrocarbons, alcohols, ketones, aldehydes, N-containing compounds, S-containing compounds, esters, oxygen heterocycles and carboxylic acids. More specifically, 148 VOCs were identified across the 37 rice lines, of which 48 (32.4%) including 2-acetyl-1-pyrroline (2-AP) appeared to elucidate the difference between non-aromatic and aromatic rice. Furthermore, 41 (27.7%) VOCs were found to be significantly correlated with 2-AP abundance, the principle rice aroma compound. Amongst the 41 VOCs, only ten compounds were found to contribute highly towards variation in 2-AP abundance, indicative of their possible modulation roles in regard to rice aroma. Within the ten influential volatiles, three aroma active compounds; toluene, 1-hexanol, 2-ethyl and heptane, 2,2,4,6,6-pentamethyl- were established as the most reliable biochemical surrogates to the rice aroma trait. Thus, the aforementioned compounds may be used in rice breeding programme for enhancing development of the grain aroma trait.

Continuous Storage Root Formation and Bulking in Sweetpotato.

This study investigated the phenotypic variation of continuous storage root formation and bulking (CSRFAB) growth patterns underlying the development of sweetpotato genotypes for identification of potential varieties adapted to piecemeal harvesting for small scale farmers. The research was conducted between September 2016 and August 2017 in Uganda. Genotypes from two distinct sweetpotato genepool populations (Population Uganda A and Population Uganda B) comprising 130 genotypes, previously separated using 31 simple sequence repeat (SSR) markers were used. Measurements (4 harvest times with 4 plants each) were repeated on genotypes in a randomized complete block design with 2 replications in 2 locations for 2 seasons. We developed a scoring scale of 1 to 9 and used it to compare growth changes between consecutive harvests. Data analysis was done using residual or restricted maximum likelihood (REML). Data showed a non-linear growth pattern within and between locations, seasons, and genotypes for most traits. Some genotypes displayed early initiation and increase of bulking, while others showed late initiation. Broad sense heritability of CSRFAB was low due to large GxE interactions but higher in other traits probably due to high genetic influence and the effectiveness of the methodology. A high level of reproducibility (89%) was observed comparing 2016B and 2017A seasons (A and B are first and second season, respectively) at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda. Choosing CSRFAB genotypes can more than double the sweetpotato production (average maximum yield of 13.1 t/ha for discontinuous storage root formation and bulking (DSRFAB) versus 28.6 t/ha for CSRFAB, demonstrating the importance of this underresearched component of storage root yield.

Continuous Storage Root Formation and Bulking in Sweetpotato

This study investigated the phenotypic variation of continuous storage root formation and bulking (CSRFAB) growth patterns underlying the development of sweetpotato genotypes for identification of potential varieties adapted to piecemeal harvesting for small scale farmers. The research was conducted between September 2016 and August 2017 in Uganda. Genotypes from two distinct sweetpotato genepool populations (Population Uganda A and Population Uganda B) comprising 130 genotypes, previously separated using 31 simple sequence repeat (SSR) markers were used. Measurements (4 harvest times with 4 plants each) were repeated on genotypes in a randomized complete block design with 2 replications in 2 locations for 2 seasons. We developed a scoring scale of 1 to 9 and used it to compare growth changes between consecutive harvests. Data analysis was done using residual or restricted maximum likelihood (REML) in GenStat 18th Edition. There were strong linear and quadratic trends over time (P&lt;0.001) indicating a non-linear growth pattern within and between locations, seasons, and genotypes for most traits. Some genotypes displayed early initiation and a determinate linear increase of bulking, while others showed late initiation following a quadratic growth pattern. Broad sense heritability of CSRFAB would be low due to large GxE interactions, however, it was relatively high (50.5%) compared to other yield related traits indicating high genetic influence and accuracy of the developed method to quantify yield overtime. A high level of reproducibility (89%) was observed comparing 2016B and 2017A seasons (A and B are first and second season, respectively) at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda. Choosing CSRFAB genotypes can more than double the sweetpotato production (average maximum yield of 13.1 t/ha for discontinuous storage root formation and bulking (DSRFAB) versus 28.6 t/ha for CSRFAB demonstrating the importance of this underresearched component of storage root yield.

English

This study was done to determine the mid-parent heterosis, the general (GCA) and specific (SCA) combining abilities of storage root yield, sweet potato virus resistance (SPVD), flesh color and vine weight of candidate sweet potato clones. Sixteen selected genotypes from two gene pools were crossed in an 8B&times;8A cross having 64 families. Trials were conducted with 1,896 offsprings and 16 parents during two seasons at the National Crops Resources Research Institute in Uganda (NaCRRI) using a Westcott design (only checks were replicated). Significant differences in performance were noted among families for all traits in both seasons (P &le; 0.001). Magabali&times;NK259L and Resisto&times;Naspot 7 were the best crosses for improving total storage root while Naspot 5&times;Naspot 7 stood out as the best cross for flesh color. The ratio of general combining ability to specific combining ability (GCA/SCA) for storage root, flesh color and SPVD ranged from 0.55 to 0.79, implying that additive gene effects were more important than non-additive gene effects for these traits.&nbsp; For vine weight, non-additive gene effects tended to be predominant.&nbsp; A susceptible parent Magabali and a moderately susceptible parent Naspot 1 had the most resistant progenies. This suggests that SPVD resistant alleles could be homozygous recessive, which may be confirmed in further studies. Correlation studies between traits were almost all significant except for flesh color and storage root yield. There was a positive and significant correlation (P &le; 0.001) between flesh color and SPVD resistance, with orange roots being the most resistant to SPVD. This important finding can help breeders to come up with orange-fleshed sweet potatoes that are highly resistant to virus diseases. Key words: Sweet potato combining ability, heterosis, genetic effect, storage root, sweet potato virus resistance (SVDP), flesh color, vine weight. &nbsp

Continuous Storage Root Formation and Bulking in Sweetpotato

This study investigated the phenotypic variation of continuous storage root formation and bulking (CSRFAB) growth patterns underlying the development of sweetpotato genotypes for identification of potential varieties adapted to piecemeal harvesting for small scale farmers. The research was conducted between September 2016 and August 2017 in Uganda. Genotypes from two distinct sweetpotato genepool populations (Population Uganda A and Population Uganda B) comprising 130 genotypes, previously separated using 31 simple sequence repeat (SSR) markers were used. Measurements (4 harvest times with 4 plants each) were repeated on genotypes in a randomized complete block design with 2 replications in 2 locations for 2 seasons. We developed a scoring scale of 1 to 9 and used it to compare growth changes between consecutive harvests. Data analysis was done using residual or restricted maximum likelihood (REML) in GenStat 18th Edition. There were strong linear and quadratic trends over time (P&lt;0.001) indicating a non-linear growth pattern within and between locations, seasons, and genotypes for most traits. Some genotypes displayed early initiation and a determinate linear increase of bulking, while others showed late initiation following a quadratic growth pattern. Broad sense heritability of CSRFAB would be low due to large GxE interactions, however, it was relatively high (50.5%) compared to other yield related traits indicating high genetic influence and accuracy of the developed method to quantify yield overtime. A high level of reproducibility (89%) was observed comparing 2017A and 2017B seasons (A and B are first and second season, respectively) at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda. Choosing CSRFAB genotypes can more than double the sweetpotato production (average maximum yield of 13.1 t/ha for discontinuous storage root formation and bulking (DSRFAB) versus 28.6 t/ha for CSRFAB demonstrating the importance of this underresearched component of storage root yield.

Genetic Variation and Trait Correlations in an East African Cassava Breeding Population for Genomic Selection.

Cassava (Manihot esculenta Crantz) is a major source of dietary carbohydrates for >700 million people globally. However, its long breeding cycle has slowed the rate of genetic gain for target traits. This study aimed to asses genetic variation, the level of inbreeding, and trait correlations in genomic selection breeding cycles. We used phenotypic and genotypic data from the National Crops Resources Research Institute (NaCRRI) foundation population (Cycle 0, C0) and the progeny (Cycle 1, C1) derived from crosses of 100 selected C0 clones as progenitors, both to evaluate and optimize genomic selection. The highest broad-sense heritability (H2 = 0.95) and narrow-sense heritability (h2 = 0.81) were recorded for cassava mosaic disease severity and the lowest for root weight per plot (H2 = 0.06 and h2 = 0.00). We observed the highest genetic correlation (rg= 0.80) between cassava brown streak disease root incidence measured at seedling and clonal stages of evaluation, suggesting the usefulness of seedling data in predicting clonal performance for cassava brown streak root necrosis. Similarly, high genetic correlations were observed between cassava brown streak disease severity (rg= 0.83) scored at 3 and 6 mo after planting (MAP) and cassava mosaic disease, scored at 3 and 6 MAP (rg= 0.95), indicating that data obtained on these two diseases at 6 MAP would suffice. Population differentiation between C0 and C1 was not well defined, implying that the 100 selected progenitors of C1 captured the diversity in the C0. Overall, genetic gain for most traits were observed from C0 to C1.

Continuous Storage Root Formation and Bulking in Sweetpotato

This study investigated the phenotypic variation of continuous storage root formation and bulking (CSRFAB) growth patterns underlying the development of sweetpotato genotypes for identification of potential varieties adapted to piecemeal harvesting for small scale farmers. The research was conducted between September 2016 and August 2017 in Uganda. Genotypes from two distinct sweetpotato genepool populations (Population Uganda A and Population Uganda B) comprising 130 genotypes, previously separated using 31 simple sequence repeat (SSR) markers were used. Measurements (4 harvest times with 4 plants each) were repeated on genotypes in a randomized complete block design with 2 replications in 2 locations for 2 seasons. We developed a scoring scale of 1 to 9 and used it to compare growth changes between consecutive harvests. Data analysis was done using residual or restricted maximum likelihood (REML). Data showed a non-linear growth pattern within and between locations, seasons, and genotypes for most traits. Some genotypes displayed early initiation and increase of bulking, while others showed late initiation. Broad sense heritability of CSRFAB was low due to large GxE interactions but higher in other traits probably due to high genetic influence and the effectiveness of the methodology. A high level of reproducibility (89%) was observed comparing 2016B and 2017A seasons (A and B are first and second season, respectively) at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda. Choosing CSRFAB genotypes can more than double the sweetpotato production (average maximum yield of 13.1 t/ha for discontinuous storage root formation and bulking (DSRFAB) versus 28.6 t/ha for CSRFAB, demonstrating the importance of this underresearched component of storage root yield.

Training Population Optimization for Prediction of Cassava Brown Streak Disease Resistance in West African Clones.

Cassava production in the central, southern and eastern parts of Africa is under threat by cassava brown streak virus (CBSV). Yield losses of up to 100% occur in cases of severe infections of edible roots. Easy illegal movement of planting materials across African countries, and long-range movement of the virus vector (Bemisia tabaci) may facilitate spread of CBSV to West Africa. Thus, effort to pre-emptively breed for CBSD resistance in W. Africa is critical. Genomic selection (GS) has become the main approach for cassava breeding, as costs of genotyping per sample have declined. Using phenotypic and genotypic data (genotyping-by-sequencing), followed by imputation to whole genome sequence (WGS) for 922 clones from National Crops Resources Research Institute, Namulonge, Uganda as a training population (TP), we predicted CBSD symptoms for 35 genotyped W. African clones, evaluated in Uganda. The highest prediction accuracy (r = 0.44) was observed for cassava brown streak disease severity scored at three months (CBSD3s) in the W. African clones using WGS-imputed markers. Optimized TPs gave higher prediction accuracies for CBSD3s and CBSD6s than random TPs of the same size. Inclusion of CBSD QTL chromosome markers as kernels, increased prediction accuracies for CBSD3s and CBSD6s. Similarly, WGS imputation of markers increased prediction accuracies for CBSD3s and for cassava brown streak disease root severity (CBSDRs), but not for CBSD6s. Based on these results we recommend TP optimization, inclusion of CBSD QTL markers in genomic prediction models, and the use of high-density (WGS-imputed) markers for CBSD predictions across population.

English

Rice blast caused by Magnaporthe grisea is an economically important disease which distributed in most rice growing areas of the world. Yield losses up to 100% are attributed to the blast disease in different rice growing regions of Uganda. In order to combat this disease screening of forty-six introduced Korean rice accessions and two checks IR-64 (resistant) and NERICA-1 (susceptible) were done in a 6 by 8 alpha lattice design in two replications under natural infestation in field conditions, and three replications in the screen house at National Crops Resources Research Institute (NaCRRI) of Uganda in 2015, A and B seasons. Final leaf blast severity, lesion size, area under disease progress curve (AUDPC) values, panicle blast and grain yield were highly significant among genotypes. Genotypes SRHB-133, SRHB-93 and SRHB-78 were resistant to rice blast in both field and screenhouse conditions and showed a lower lesion size. Therefore, these genotypes that consistently showed resistance to rice blast disease can be used as a source of resistance gene for rice blast. This leads to conclude that screening in both the field across seasons and confirming their resistance in the screen house helps the breeder to identify the genotypes that are truly resistant for further utilization as resistant sources. Key words: Rice blast, screening, Magnaporthe grisea, Uganda.