The use of multiplexed simple sequence repeat (SSR) markers for analysis of genetic diversity in African rice genotypes

Rice is an emerging food and cash crop in Eastern Africa. Thousands of germplasm accessions have been introduced from major rice breeding centers, such as the International Rice Research Institute (IRRI), and Africa Rice but the genetic variability among the introduced rice germplasm is unknown. Knowledge on genetic diversity would be useful in designing measures for comprehensive breeding and conservation. To address this knowledge gap, 10 highly polymorphic rice simple sequence repeat (SSR) markers were used to characterize 99 rice genotypes to determine their diversity and place them in their different population groups. The SSR markers were multiplexed in 3 panels to increase their throughput. An average of 15.9 alleles was detected, ranging from 6 alleles detected by marker RM7 to 30 by marker RM333. The UPGMA dendogram based on Nei’s genetic distance cluster analysis, revealed 5 genetic groups among the genotypes tested. Analysis of molecular variance indicated that 97% of the diversity observed was explained by differences in the genotypes themselves, and only 3% was due to the sources from which the genotypes were obtained. This study sets the stage for further diversity analysis of all the available germplasm lines using SSR markers to ensure effective utilization and conservation of the germplasm.Keywords: Genetic diversity, simple sequences repeat (SSR) markers, multiplexing, rice genotypes, structure. Abbreviation: IRRI, International Rice Research Institute; SSR, simple sequence repeat; NaCRRI, national crops resources research institute; RAPD, random amplified polymorphic DNA; AFLP, amplified fragment length polymorphisms; RFLP, restriction fragment length polymorphisms; SNP, single nucleotide polymorphisms; BAC, bacterial artificial chromosome; PAC, P1-derived artificial chromosome; PCR, polymerase chain reaction; Ho, heterozygosity; He, heterozygosity

Influence of spectral properties on cassava leaf development and metabolism

Cassava’s importance as a food security crop in Sub Saharan Africa will be enhanced by its special traits such as tolerance to drought and high yields under hydrothermal stress. Some of the special traits which include the light reflective and absorptive properties of the leaves that depend on the surface characteristics of the leaves, are variety dependent and may influence the plants’ reaction to light; hence, its photosynthetic capacity. We investigated the differences in the leaf spectral properties in different cassava varieties and related them to leaf biochemical properties using 20 cassava varieties established in a randomized complete block design in Kasese, western Uganda. Time dependent changes in leaf spectral characteristics were studied using Digimizer software and related to changes in sugar and pigment properties. Changes in the amount of reflected light were observed for the three main wavelengths used by plants (blue, green and red) with the blue being the most preferred. Total soluble free sugars exhibited a diurnal pattern from lower values (0.07 mg/g) after the dark period to higher values (0.313 mg/g) as the day progressed and was different from those of translocatable sugars such as sucrose. Chlorophyll a exhibited a curved pattern in all varieties increasing with increase in light intensity from 09:00 h (0.18 ug/g), peaking at 15:00 h (0.22 ug/g) and dropping down in concentration by 18:00 h (0.16 ug/g). Significant differences were observed in cassava varieties for the concentration of chlorophylls and carotenes. The results were obtained at a time of optimal growth conditions (four months after planting) and were used to classify these varieties into three broad groups showing that studies on spectral properties of leaves can still give a lot of insights in selection for stress tolerance under less optimal stress. The significant changes observed in the phenotype especially the foliar portion of the plant with the stay green and early recovering mechanisms of tolerance identified also tarried well with observed spectral differences. The results show that studies on plant spectral properties can be important in making inferences on the plants physiological and growth status.Keywords: Spectral properties, tolerance mechanisms, physiology, reflectance

Improvement of resistance to fusarium root rot through gene pyramiding in common bean

Fusarium root rot (FRR), caused by Fusarium solani f.sp. phaseoli , is one of the most serious root rot diseases of common bean ( Phaseolus vulgaris L.) throughout the world. Yield losses of up to 84% have been attributed to the disease. Development and deployment of resistant materials is the most feasible approach to managing the disease. The objective of this study was to estimate the number of pyramided Fusarium root rot resistance genes among the four resistant lines and determine their effectiveness in improving levels of resistance to Fusarium root rot in the susceptible bean cultivars. Crosses among four Fusarium root rot (Fusarium solani f.sp. phaseoli) resistant common bean (Phaseolus vulgaris) were developed. They involved six inbred lines, MLB-48-89A (M48), MLB-49-89A (M49), G2333 (G2) and G685 (G6), and two susceptible cultivars, K20 and Kanyebwa, The resistant lines were used to develop a double cross (DC) population. The DC F1 and each resistant parent were crossed to each of the two susceptible cultivars to form five-parent and single crosses, respectively. Developed populations were subjected to Fusarium solani f. sp. phasoeli isolate-3 under screenhouse conditions. There were segregation ratios of 15:1 (\u3c72 = 1.89, P = 0.17), 61:3 (\u3c72 = 0.18, P = 0.67) and 249:7 (\u3c72 = 1.74, P = 0.19) indicating that two, three and four genes independently condition resistance to F. solani in lines G2 x G6, M49 x M48 and (M49 x M48) x (G2 x G6). A good fit of only four genes in the double cross compared to two in the G2 x G6 , and three genes in the M49 x M48 cross suggests that at least one parent in the G2 x G6 cross have the same or closely linked genes as a parent in the M49 x M48 cross. The F1 means of the five-parent cross (FPC) involving either susceptible parent had lower disease scores, though not significantly (P > 0.05), than the single-crosses from that parent. The F2 of both FPC showed less disease than the single-cross (SC) means (P < 0.05) compared to the single-cross (SC) while the F2 of both FPC had a significant negative deviation (P < 0.05). The F2 frequency distributions also showed that the FPC in both Kanyebwa and K20 populations had higher proportions of resistant plants than any of the single crosses in the respective populations. The superior performance of the FPC over the SC demonstrates that combining resistance genes form different FRR resistance sources can provide a stable source of resistance than using single sources of resistance.Pourriture racinaire caus\ue9e par Fusarium solani f.sp. phaseoli est l\u2019une des plus dang\ue9reuses pourritures racinaires du haricot commun ( Phaseolus vulgaris L.) partout dans le monde. La maladie cause des pertes de rendement jusqu\u2019\ue0 84%. L\u2019objectif de cette \ue9tude \ue9tait d\u2019estimer le nombre de combinaisons de g\ue8nes de r\ue9sistance \ue0 la pourriture racinaire due au Fusarium parmi 4 lign\ue9es r\ue9sistantes et d\ue9terminer leur efficacit\ue9 dans l\u2019am\ue9lioration des niveaux de r\ue9sistance \ue0 la pourriture racinaire dans les vari\ue9t\ue9s sensibles. Les croisements ont \ue9t\ue9 d\ue9velopp\ue9s parmi les 4 vari\ue9t\ue9s de haricot commun r\ue9sistantes au Fusarium. Les croisements impliquaient six lign\ue9es, MLB48-89A, MLB-49-89A, G2333 et G685, et deux vari\ue9t\ue9s sensibles, K20 et Kanyebwa. Les lign\ue9es r\ue9sistantes \ue9taient utilis\ue9es pour d\ue9velopper une population \ue0 double croisement. Les individus de la g\ue9n\ue9ration F1 du double croisement et chaque parent r\ue9sistant \ue9taient crois\ue9s \ue0 chacun des deux cultivars sensibles pour former des croisements \ue0 cinq parents et simples, respectivement. Les populations d\ue9velopp\ue9es \ue9taient soumises \ue0 l\u2019isolat3 du Fusarium solani f.sp. phaseoli en serre. Les rapports de s\ue9gr\ue9gation \ue9taient de 15:1 (\u3c72 = 1.89, P = 0.17), 61:3 (\u3c72 = 0.18, P = 0.67) et 249:7 (\u3c72 = 1.74, P = 0.19), montrant que deux, trois et quatre g\ue8nes conditionnent ind\ue9pendamment la r\ue9sistance au F. solani dans les lign\ue9es G2 x G6, M49 x M48 et (M49 x M48) x (G2 x G6). Une bon adjustement de quatre g\ue8nes seulement dans le double croisement compar\ue9 \ue0 deux dans le croisement G2 x G6, et trois g\ue8nes dans le croisement M49 x M48 indique qu\u2019au moins un parent dans le croisement a les m\ueames g\ue8nes ou les g\ue8nes \ue9troitement li\ue9s pour un parent dans le croisement M49 x M48. Les moyennes des F1 issues des croisements \ue0 cinq parents impliquant le parent Kanyebwa et les populations de K20 avaient des d\ue9viations n\ue9gatives non significatives (P > 0.05) compar\ue9 au croisement simple. D\u2019autre part, les F2 des deux croisements \ue0 cinq parents avaient des d\ue9viations n\ue9gatives significatives (P < 0.05) issues des moyennes de croisements simples, ce qui indique une s\ue9v\ue9rit\ue9 des sympt\uf4mes de la pourriture racinaire plus faible dans les croisements \ue0 cinq parents que dans les simples croisements. La fr\ue9quence des distributions des F2 montrait aussi que les croisements \ue0 cinq parents \ue0 la fois dans les populations de Kanyebwa et celles de K20 avaient des proportions des plants r\ue9sistants plus \ue9lev\ue9es que toutes celles des croisements simples dans les populations respectives

DYNAMICS OF Cercospora zeina POPULATIONS IN MAIZE-BASED AGRO-ECOLOGIES OF UGANDA

Stability of pathogen populations characterised by slow temporal variation is important for durability of disease management systems in any agroecology. Temporal variation in population structure is attributed to factors related to ecology, biology and life history, and varies among organisms and ecosystems. The objective of this study was to investigate genetic variability of Cercospora zeina (previously called Cercospora zeae-maydis Type II) populations in maize ( Zea mays ) producing areas under Uganda conditions. Populations of the fungus were analysed for genetic variability using a fluorescent amplified fragment length polymorphism (AFLP) technique. Little or no genetic differentiation (\u3a6FST 0.05) was detected for populations sampled within the same year, within an agroecology. However, a weak to moderate population structure was detected between populations from different locations, within the same (\u3a6FST = 0.08) or different agroecologies (\u3a6FST = 0.09). Pair-wise comparisons using \u3a6FST gene diversity and genetic distance, showed a reduction in genetic diversity in younger populations, suggestive of minor effects of selection and genetic drift. Overall, the data suggest that during the 3 years of study the impact of selection and genetic drift on C. zeina populations in the two Ugandan agroecologies is slow, but progressive leading to homogenetity with agroecologies and differences between agroecologies.La stabilit\ue9 des populations d\u2019agents pathog\ue8nes caract\ue9ris\ue9e par une faible variation dans le temps, est importante pour la durabilit\ue9 dans les syst\ue8mes de gestion des pathologies des plantes dans n\u2019importe quelle zone agro-\ue9cologique. La variation dans le temps au sein d\u2019une population, est fonction de facteurs relatifs \ue0 l\u2019\ue9cologie, la biologie et l\u2019histoire de vie des pathog\ue8nes. Elle varie d\u2019un \ueatre vivant \ue0 un autre et d\u2019un \ue9cosyst\ue8me \ue0 un autre. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer la variabilit\ue9 g\ue9n\ue9tique au sein des populations de Cercospora zeina (pr\ue9cedemment appel\ue9 Cercospora zeae-maydis Type II) dans les zones productrice de ma\uefs ( Zea mays ) en Ouganda. Les populations de ce champignon microscopique ont \ue9t\ue9 soumises \ue0 une \ue9tude de variabilit\ue9 g\ue9n\ue9tique gr\ue2ce \ue0 la technique du polymorphisme de longueur de fragments amplifi\ue9s (AFLP). Tr\ue8s peu ou aucune variation g\ue9n\ue9tique (\u3a6FST 0.05) n\u2019a \ue9t\ue9 observ\ue9e pour les populations \ue9chantillonn\ue9es au cours de la m\ueame ann\ue9e, dans une zone agro-\ue9cologique donn\ue9e. N\ue9anmoins, une structure populationnelle d\u2019envergure faible \ue0 mod\ue9r\ue9e a \ue9t\ue9 observ\ue9e entre les populations de diff\ue9rentes origines, (\u3a6FST = 0.08) \ue0 l\u2019int\ue9rieur d\u2019une m\ueame population ou (\u3a6FST = 0.09) entre les populations de diff\ue9rente zones agro \ue9cologique. La comparaison par paires utilisant \u3a6FST diversit\ue9 des g\ue8nes et distance g\ue9n\ue9tique, a montr\ue9 une r\ue9duction de diversit\ue9 g\ue9n\ue9tique dans les populations les plus jeunes, sugg\ue9rant ainsi un effet mineur de s\ue9lection et de d\ue9rive g\ue9n\ue9tique. Au total, les donn\ue9es collect\ue9es indiquent un faible impact de s\ue9lection et de d\ue9rive g\ue9n\ue9tique sur les populations de C. zeina dans les deux zones agro-\ue9cologiques Ougandaise durant les 3 ann\ue9es de l\u2019\ue9tude, mais cet impact est progressif et responsable de l\u2019homog\ue9n\ue9it\ue9 au sein des zones agro-\ue9cologiques et des diff\ue9rences entre les zones agro-\ue9cologiques

QTL Mapping of Traits Associated with Dual Resistance to the African Stem Borer (Busseola fusca) and Spotted Stem Borer (Chilo partellus) in Sorghum (Sorghum bicolor)

Sorghum (Sorghum bicolor (L.) Moench) is an important food crop in semi-arid tropics. The crop grain yield ranges from 0.5 t/ha to 0.8 t/ha compared to potential yields of 10 t/ha. The African stem borer Busseola fusca Fuller (Noctuidae) and the spotted stem borer Chilo partellus Swinhoe (Crambidae), are among the most economically important insect pests of sorghum. The two borers can cause 15% - 80% grain yield loss in sorghum. Mapping of QTLs associated with resistance traits to the two stem borers is important towards marker-assisted breeding. The objective of this study was to map QTLs associated with resistance traits to B. fusca and C. partellus in sorghum. 243 F9:10 sorghum RILs derived from ICSV 745 (S) and PB 15520-1 (R) were selected for the study with 4,955 SNP markers. The RILs were evaluated in three sites. Data was collected on leaf feeding, deadheart, exit holes, stem tunnels, leaf toughness, seedling vigour, bloom waxiness, and leaf glossiness. ANOVA for all the traits was done using Genstat statistical software. Insect damage traits and morphological traits were correlated using Pearson’s correlation coefficients. Genetic mapping was done using JoinMap 4 software, while QTL analysis was done using PLABQTL software. A likelihood odds ratio (LOD) score of 3.0 was used to declare linkage. Joint analyses across borer species and sites revealed 4 QTLs controlling deadheart formation; 6 controlling leaf feeding damage; 5 controlling exit holes and stem tunneling damages; 2 controlling bloom waxiness, leaf glossiness, and seedling vigour; 4 conditioning trichome density; and 6 conditioning leaf toughness. Joint analyses for B. fusca and C. partellus further revealed that marker CS132-2 colocalised for leaf toughness and stem tunneling traits on QTLs 1 and 2, respectively; thus, the two traits can be improved using the same linked marker. This study recommended further studies to identify gene(s) underlying the mapped QTLs

STABILITY AND EXTENT OF RESISTANCE OF COWPEA LINES TO FLOWER BUD THRIPS IN UGANDA

Cowpea ( Vigna unguiculata (L.) Walp.) is a legume attacked by several field insect pests, with flower thrips ( Megalurothrips sjostedti Trybom) being the most damaging. It causes 20 to 100% yield losses. Cowpea constitutes an important source of protein for resource poor households in Africa. The objective of this study was to identify cowpea lines that are resistant to flower thrips as a step in developing sustainable thrips management strategies. Seventy two cowpea cultivars were screened in three locations and two rainy seasons in Uganda, for thrips damage and yield components. Up to 11 cultivars (IT2841*Brown (1.50), MU20B (1.58), EBELAT*NE39 (1.61), WC17 (1.63), WC29 (1.65), MU24C (1.65), WC5 (1.66), NE46 (1.67), WC30 (1.68), NE67 (1.69), and NE51 (1.71)) were the most resistant and stable across locations. However, thrips damage was negatively correlated with the number of days to flowering (r = -0.32), indicating that the resistance in the cultivars was explained by the flower thrips infestation escape due to later flowering. Cultivar MU9 was high yielding (813.87 kg ha-1) and the most adapted genotype to all the locations; while cultivars WC26, NE48, and NE5 were the most adapted to Arua and Serere, and WC48A was the most adapted to Makerere University Agricultural Research Institute, Kabanyolo (MUARIK). There is potential of finding resistance sources in the cultivars tested.Le ni\ue9b\ue9 ( Vigna unguiculata (L.) Walp.) est une l\ue9gumineuse attaqu\ue9e par plusieurs insectes au champ avec thrips ( Megalurothrips sjostedti Trybom) le plus nuisible causant 20-100% de perte de rendement. Le ni\ue9b\ue9 constitue une source de prot\ue9ine bon-march\ue9 pour beaucoup de pauvres m\ue9nages en Afrique. L\u2019objectif de cette \ue9tude \ue9tait d\u2019identifier des vari\ue9t\ue9s plus r\ue9sistantes au thrips pour le d\ue9veloppement des strat\ue9gies de lutte durable. Soixante-douze vari\ue9t\ue9s du ni\ue9b\ue9 ont \ue9t\ue9 \ue9valu\ue9es dans trois environnements pendant deux saisons en Uganda pour les dommages, le rendement et ses composantes. Les donn\ue9es ont \ue9t\ue9 soumises aux analyses de variance et biplot de l\u2019effet de g\ue9notype et l\u2019interaction entre g\ue9notype et environnement (GGE). Les r\ue9sultats ont montr\ue9 un effet significatif (P<0.001) de l\u2019interaction entre g\ue9notype, environnement pour les scores de dommages caus\ue9s par thrips. Les vari\ue9t\ue9s les plus r\ue9sistantes et stables \ue9taient IT2841*Brown (1.50), MU20B (1.58), EBELAT*NE39 (1.61), WC17 (1.63), WC29 (1.65), MU24C (1.65), WC5 (1.66), NE46 (1.67), WC30 (1.68), NE67 (1.69), and NE51 (1.71). Toutefois, une corr\ue9lation n\ue9gative (r = -0.32) a \ue9t\ue9 observ\ue9e entre les scores de dommage et le nombre de jours de floraison indiquant que la r\ue9sistance observ\ue9e, \ue9tait due \ue0 un \ue9chappement par une floraison tardive. Le cultivar MU9 avait le rendement le plus \ue9lev\ue9 (813, 87 kg ha-1) et constituait le plus adapt\ue9 aux diff\ue9rents environnements alors que les cultivars WC26, NE48, and NE5 \ue9taient les plus adapt\ue9s \ue0 Arua et Serere, et WC48A \ue9tait le plus adapt\ue9 \ue0 l\u2019Institut de Recherches Agricoles de l\u2019Universit\ue9 de Makerere, Kabanyolo (MUARIK). Il y a potentiel de trouver de source de r\ue9sistance parmi les vari\ue9t\ue9s \ue9valu\ue9es

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.Le germoplasme est une source pr\ue9cieuse de diversit\ue9 g\ue9n\ue9tique qui soutient les efforts d\u2019am\ue9lioration des cultures dans tout programme de s\ue9lection, mais il doit d\u2019abord \ueatre enti\ue8rement caract\ue9ris\ue9 pour ses traits \ue9conomiquement pr\ue9cieux avant de pouvoir \ueatre utilis\ue9 efficacement. Dans le riz ( Oryza sativa ), le d\ue9veloppement de nouvelles vari\ue9t\ue9s avec un ar\uf4me am\ue9lior\ue9 n\ue9cessite un ph\ue9notypage correct et une connaissance pr\ue9alable des g\ue8nes et all\ue8les disponibles r\ue9gissant le caract\ue8re aromatique dans le pool g\ue9n\ue9tique. Un ph\ue9notypage et un g\ue9notypage corrects peuvent \ueatre obtenus en utilisant des m\ue9thodes sensorielles et des marqueurs fonctionnels associ\ue9s \ue0 des polymorphismes qui d\ue9finissent les g\ue8nes aromatiques. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer le statut aromatique des accessions de riz et d\u2019\ue9valuer les diff\ue9rents all\ue8les du g\ue8ne badh2 \ue0 l\u2019aide de marqueurs fonctionnels. Un total de 56 accessions de riz ont \ue9t\ue9 \ue9valu\ue9es au National Crops Resources Research Institute (NaCRRI) en Ouganda pour leur ar\uf4me en utilisant des m\ue9thodes sensorielles et un marqueur mol\ue9culaire pour diff\ue9rencier les accessions aromatiques et non aromatiques. Les accessions aromatiques ont ensuite \ue9t\ue9 \ue9valu\ue9es pour les variations au sein du g\ue8ne de la b\ue9ta\uefne ald\ue9hyde d\ue9shydrog\ue9nase2 (badh2) responsable de l\u2019ar\uf4me du riz \ue0 l\u2019aide de marqueurs fonctionnels. L\u2019\ue9valuation sensorielle de l\u2019ar\uf4me a identifi\ue9 23 accessions comme aromatiques; tandis que 33 \ue9taient non aromatiques. Les r\ue9sultats mol\ue9culaires ont identifi\ue9 20 accessions comme aromatiques; tandis que 36 accessions n\u2019\ue9taient pas aromatiques. L\u2019analyse des marqueurs fonctionnels a indiqu\ue9 la pr\ue9sence d\u2019all\ue8les badh2-E7 dans 20 accessions aromatiques de cette collection qui pourraient \ueatre utilis\ue9es dans le programme de s\ue9lection pour le trait aromatique du riz

New sources of resistance to spotted stem borer, Chilo partellus in sorghum

The lepidopteran Chilo partellus Crambid, an introduced pest in East and southern Africa from Asia, is the most economically important stem borer species infesting cereals in Africa. Chilo partellus causes more than 40% yield loss in sorghum in East Africa. Cultural strategies, biological control using parasitoids, as well as pesticides are being employed, but are either ineffective or uneconomic for resource constrained farmers in cereal production. Thus host resistance remains the most economic viable strategy. Sorghum is an African crop and has thus co-evolved with several pests, inherently developing resistance to them as well as C. partellus. Moreover, C. partellus is exotic with limited sources of resistance in local sorghum. Sorghum from other ecologies with a long history of C. partellus infestation could thus provide additional and new sources of resistance. The objective of this study was to evaluate a panel of local and exotic sorghum genotypes for resistance to C. partellus. Seven genotypes from East Africa and twenty from India were evaluated at Kiboko, Kenya, for tolerance/resistance to C. partellus during long- and short-rainy seasons of 2010. Test plants were artificially infested with five stem borer neonates, and data were recorded on leaf feeding, deadhearts, stem tunneling and exit holes as well as agronomic parameters. Based on selection index generated, genotypes ICSA 472, ICSA 473, ICSV 700 and ICSA 464 were resistant owing to antibiosis and antixenosis mechanisms of resistance. These genotypes can be used in sorghum improvement to develop cultivars with high grain yield and resistance to C. partellus.

HERITABILITY, COMBINING ABILITY AND INHERITANCE OF STORAGE ROOT DRY MATTER IN YAM BEANS

Storage root dry matter content (RDM) is central to the improvement of consumer and industrial attributes of root crops. Yam bean ( Pachyrhizus species) is a legume root crop newly introduced in Uganda, but its adoption may be constrained by low RDM. The objective of this study was to investigate the magnitude of variance for general combining ability (GCA) and specific combining ability (SCA) effects, heritability estimates and inheritance of RDM in yam beans. Progenies of sixteen crosses, generated using the North Carolina (NCII) mating scheme, were evaluated in F1 and F2 field experiments, with three replications at the National Crops Resources Research Institute (NaCRRI), Namulonge in Central Uganda, during the first cropping seasons of April, 2013 and 2014, respectively. Significant (p<0.001) mean squares for general combining ability (GCA), and specific combining ability (SCA) were observed in F1 and F2 generations, demonstrating additive and non-additive genetic inheritance of RDM. High Baker\u2019s ratio in F1 (0.76) and F2 (0.78), and large \u3c32GCA/ \u3c32SCA (3.13) indicate predominance of additive gene effects. Narrow sense heritability was high in both F1 (0.74) and F2 (0.75), implying that RDM can be improved in yam beans through selection. The results provide a basis for selection of suitable parents for hybridisation and breeding programmes to develop high dry matter yam bean varieties in Uganda.La teneur en mati\ue8res \ue8che du stock racinaire (MSR) est essentiel en terme d\u2019am\ue9lioration des qualit\ue9s des cultures racinaires pour les consommateurs et d\u2019industriels. Le haricot-igname (esp\ue8ce Pachyrhizus ) est une culture racinaire l\ue9gumineuse nouvellement introduite en Ouganda, mais son adoption pourrait \ueatre handicap\ue9e par sateneur basse en mati\ue8res \ue8che racinaire. Cette \ue9tude avait pour objectif d\u2019\ue9tudier le niveau de la variance pour les effets de la capacit\ue9 de combinaison g\ue9n\ue9rale et la capacit\ue9 de combinaison sp\ue9cifique, estimations de l\u2019h\ue9ritabilit\ue9 et l\u2019h\ue9ritage de MSR dans les haricots ignames. Les prog\ue9nies de seize croisements g\ue9n\ue9r\ue9s \ue0 l\u2019aide du syst\ue8me de croisement de la Caroline du Nord (NCII), ont \ue9t\ue9 \ue9valu\ue9s dans des essais en champs de F1 et F2 avec trois r\ue9p\ue9titions \ue0 l\u2019Institut National de Recherche sur les Ressources V\ue9g\ue9tales (NaCRRI), Namulonge en Ouganda, pendant les premi\ue8res saisons culturalesd\u2019 Avril 2013 et 2014, respectivement. Les carr\ue9s moyens significatifs (P<0,001) de capacit\ue9 g\ue9n\ue9ralede combinaison et capacit\ue9 sp\ue9cifique de combinaison \ue9taient observ\ue9s dans les g\ue9n\ue9rations F1 et F2 d\ue9montrant ainsi un heritage g\ue9n\ue9tique additif et non additive de MSR. Le rapport \ue9lev\ue9 de Baker en F1 (0,76) et F2 (0,78), et \u3c32GCA/ \u3c32SCA (3.13) large indiquent la pr\ue9dominance des effets de g\ue8nes additifs. Une \ue9troite h\ue9ritabilit\ue9 d\u2019ordre de F1 (0.74) et F2 (0.75) \ue9tait observ\ue9e, ce qui implique que MSR peut \ueatre am\ue9lior\ue9 dans le haricot-igname par voie de s\ue9lection. Les r\ue9sultats constituent une base pour la s\ue9lection des parents appropri\ue9s pour les programmes d\u2019hybridation et d\u2019am\ue9lioration g\ue9n\ue9tique pour d\ue9velopper des vari\ue9t\ue9s de haricot-ignames \ue0 haute teneur en mati\ue8res\ue8 che en Ouganda

Genetic variability and gain for storage root yield and yield components in yam beans

There is limited information on the genetic parameters and genetic gain of yam bean ( Pachyrhizus species) accessions introduced to Rwanda. No comprehensive literature exists on the inheritance of yield and yield components, on segregating populations. This study investigated variability, heritability and genetic advance in F2 yam bean genotypes. Seven F2 yam bean hybrids were evaluated at the Rubona Research Station located in Southern Province of Rwanda, during growing season 2014B. Results revealed significant (P<0.01) genetic variability in plant vigour (PV), pod weight (WOP), plant height (PHT), 100 seed weight (100SW), total biomass yield (TBY), storage root yield (SRY), dry matter content (DMC), and starch content (STA). High genetic (\u3c32g) and phenotypic (\u3c32p) variances, and genotypic coefficients of variation (GCV> 25%) were observed for WOP, PHT, 100SW, TBY, DMC and STA. Estimates of heritability (H2) were high (greater than 50%) for all traits, except for seed yield, number of roots and number of pods. The GA and genetic advance, as percentage of the mean (GAM%), were high for PV, WOP, PHT, 100SW, TBY and DMC. There were positive and significant (P<0.05) associations between PV and PHT, protein content (PRO), 100SW, TBY, SRY, and DMC. Dry matter content also had positive and significant (P<0.01) correlations with STA. These results indicate presence of high genetic variability, heritability and expected genetic gain suggesting potential for genetic improvement of plant vigour, weight of pods, plant height, 100 seed weight, total biomass yield, storage root fresh yield, dry matter content and starch content of yam beans in Rwanda.Il existe peu d\u2019informations sur les param\ue8tres g\ue9n\ue9tiques et le gain g\ue9n\ue9tique des accessions de haricot-igname (esp\ue8ce Pachyrhizus ) introduites au Rwanda. Il n\u2019existe pas de litt\ue9rature compl\ue8te sur l\u2019h\ue9r\ue9dit\ue9 du rendement et des composantes du rendement, sur la s\ue9gr\ue9gation des populations. Cette \ue9tude a \ue9tudi\ue9 la variabilit\ue9, l\u2019h\ue9ritabilit\ue9 et l\u2019avanc\ue9e g\ue9n\ue9tique des g\ue9notypes de haricot-igname F2. Sept hybrides de haricot-igname F2 ont \ue9t\ue9 \ue9valu\ue9s \ue0 la Station de Recherche de Rubona situ\ue9e dans la Province M\ue9ridionale du Rwanda, pendant la saison agricole 2014B. Les r\ue9sultats ont r\ue9v\ue9l\ue9 une variabilit\ue9 g\ue9n\ue9tique significative (P <0,01) de la vigueur de la plante (PV), du poids de la gousse (WOP), de la hauteur de la plante (PHT), du poids de 100 graines (100SW), du rendement total en biomasse (TBY), du rendement des racines de stockage (SRY), teneur en mati\ue8re s\ue8che (DMC) et teneur en amidon (STA). Des variances g\ue9n\ue9tiques (\u3c32g) et ph\ue9notypiques (\u3c32p) \ue9lev\ue9es et des coefficients de variation g\ue9notypiques (GCV> 25%) ont \ue9t\ue9 observ\ue9s pour WOP, PHT, 100SW, TBY, DMC et STA. Les estimations de l\u2019h\ue9ritabilit\ue9 (H2) \ue9taient \ue9lev\ue9es (sup\ue9rieures \ue0 50%) pour tous les caract\ue8res, \ue0 l\u2019exception du rendement en graines, du nombre de racines et du nombre de gousses. Le GA et l\u2019avance g\ue9n\ue9tique, en pourcentage de la moyenne (GAM%), \ue9taient \ue9lev\ue9s pour PV, WOP, PHT, 100SW, TBY et DMC. Il y avait des associations positives et significatives (P <0,05) entre PV et PHT, la teneur en prot\ue9ines (PRO), 100SW, TBY, SRY et DMC. La teneur en mati\ue8re s\ue8che avait \ue9galement des corr\ue9lations positives et significatives (P <0,01) avec le STA. Ces r\ue9sultats indiquent la pr\ue9sence d\u2019une variabilit\ue9 g\ue9n\ue9tique, d\u2019une h\ue9ritabilit\ue9 et d\u2019un gain g\ue9n\ue9tique attendus \ue9lev\ue9s sugg\ue9rant un potentiel d\u2019am\ue9lioration g\ue9n\ue9tique de la vigueur des plantes, du poids des gousses, de la hauteur des plantes, du poids de 100 graines, du rendement total en biomasse, du rendement en racines fra\ueeches de stockage, de la teneur en mati\ue8re s\ue8che et en amidon de haricot-ignames au Rwanda