GENETIC DIVERSITY AMONG SORGHUM LANDRACES OF SOUTHWESTERN HIGHLANDS OF UGANDA

Sorghum ( Sorghum bicolor L. Moench) is an economic and staple crop in sub-Saharan Africa. The genetic diversity in its germplasm is an invaluable aid for its crop improvement. The objective of this study was to assess the existing genetic diversity among sorghum landraces in the southwestern highlands of Uganda. A total of 47 sorghum landraces, collected from southwestern highlands of Uganda, were characterised using 12 qualitative and 13 quantitative traits. The study was conducted at Kachwekano Research Farm in Kabale District, at an altitude of 2,223 m above sea level, during growing season of December 2014 to August 2015. Panicle shape and compactness were the most varied qualitative traits. Grain yield (1.23 to 11.31 t ha-1) and plant height (144.7 to 351.6 cm) were among quantitative traits that showed high variability. Days to 50% flowering (115 to 130 days) showed the least variability. Results of UPGMA cluster analysis generated a dendrogram with three clusters. Panicle weight, leaf width, stem girth, exertion length, peduncle length, panicle shape and compactness, glume colour and threshability were major traits responsible for the observed clustering (P<0.001). Principal Component Analysis revealed the largest variation contributors.Le sorgho ( Sorghum bicolor L. Moench) est une culture vivri\ue8re de grande consommation en Afrique au sud du Sahara. La diversit\ue9 g\ue9n\ue9tique au sein de son germplasm est d\u2019une valeur incalculable pour la production de semences am\ue9lior\ue9es. L\u2019objectif de la pr\ue9sente \ue9tude \ue9tait d\u2019\ue9valuer la diversit\ue9 existante au sein des cultivars des plateaux du Sud-ouest d\u2019Ouganda. Au total, 47 accessions de sorgho, collect\ue9es des plateaux du Sud-ouest d\u2019Ouganda, ont \ue9t\ue9 caract\ue9ris\ue9es en se servant de 12 traits quantitatifs et de 13 traits qualitatifs. L\u2019\ue9tude s\u2019est d\ue9roul\ue9e \ue0 la ferme de recherche de Kachwekano dans le district de Kabal\ue9, zone situ\ue9e \ue0 2223m d\u2019altitude, pendant la saison culturales de Decembre 2014 \ue0 Ao\ufbt 2015. La forme des panicules, et leur densit\ue9 \ue9taient les traits qualitatifs les plus diversifi\ue9s. Le rendement en grains (1,23 \ue0 11,31 t ha-1) et la hauteur des plants (144,7 \ue0 351,6 cm) \ue9taient les traits quantitatifs ayant pr\ue9sent\ue9 une grande variabilit\ue9. Le d\ue9lai de 50% de floraison (115 \ue0 130 jours) \ue9tait le trait le moins variable. La classification num\ue9rique a g\ue9n\ue9r\ue9 un dendrogramme avec trois groupes. Le poids des panicules, la largeur des feuilles, la circonf\ue9rence de la tige, la longeur des insertions, la longueur des p\ue9doncules, la forme des panicules et leur densit\ue9, la couleur de la glume et la facilit\ue9 au d\ue9corticage \ue9taient les traits majeurs ayant contribu\ue9 \ue0 la r\ue9partition en groupes (P<0.001). L\u2019analyse en composantes principales a r\ue9v\ue9l\ue9 les contributeurs \ue0 la plus grande variabilit\ue9

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

Genetic progress achieved in bean breeding in Uganda

Several cultivars of common bean (Phaseolus vulgaris L.) have been released in Uganda over a period of five decades, but the genetic gain to selection in respect of yield and agronomic characteristics has not been determined. This study was conducted to estimate the gain in selection over the 1960 - 2016 period, of common bean breeding in Uganda. Twenty nine bush and eleven climbing type cultivars were evaluated for yield and yield components, in three locations, during 2017B and 2018A cropping seasons. The study was carried out at the National Crop Resources Research Institute (NaCCRI), Nakabango Research Institute in central and Kwachwekano Zonal Agriculture Research Institute in southwestern Uganda. The design used was a randomised complete blocks with three replicates for the climbing types; and a 3x10 Alpha lattice design with three replicates for bush types. Significant differences (P<0.001) were recorded among cultivars for most traits in both bush and climbers, except seed number per pod (NSP). The range of genetic gain in grain yield was between 1,505 to 2,418 kg ha-1 for bush type cultivars, and 1,641 to 2,687 kg ha-1 for the climbing types. Yield has increased by16.3 and 26.3 kg ha-1 per year for bush and climbers, respectively; with a relative gain of 1.27%/year for bush types and 1.54%/year for the climbing types. Biomass yield and harvest index explained most of the variation in grain yield and number of pods per plant in climbing types. Among climbing types, biomass yield was significantly and positively correlated with grain yield per plant and grain yield per ha (P<0.05, and r= 0.87) and with grain yield per ha (P<0.01 r = 0.98) for bush types, biomass yield was significantly and positively correlated with grain yield per plant (P<0.05, and r= 0.59) and with grain yield per ha (P<0.01 r = 0.80) and harvest index (P<0.5 r = 0.80)

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

Genetics of resistance to groundnut rosette virus disease

Groundnut Rosette Virus disease (GRD) has long been regarded a major limiting biotic constraint to groundnut production in Sub-Saharan Africa (SSA). The disease is caused by a complex of three viral components that interact in a synergistic fashion resulting into severe crop losses. A study was conducted to better understand the genetics of inheritance of GRD resistance. Nineteen groundnut genotypes among which twelve F2 families populations arising from a 3x4 North Carolina II mating design, were evaluated for their percentage disease severity (PDS) and incidence (PDI). There was significant genetic variability for resistance to GRD among the materials studied with more significant additive gene action as compared to non additive. However, since specific combining ability effects were not so consistent among the F2 family populations, evaluation and testing of progenies alongside with their parents would be more meaningful and selection in the early generations would be the most effective strategy. Further, narrow sense heritability of 53% suggests that prerformance of groundnut progenies could be partly predicted by both parental and individual cross mean

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

New sources and stability of resistance to aphids in cowpea germplasm across locations in Uganda

Open Access ArticleThe cowpea aphid (Aphis craccivora Koch) is an economically important pest, whose feeding effects cause stunting, delayed flower initiation and yield reduction in cowpea (Vigna unguiculata L. Walp). Host plant resistance offers an alternative for controlling aphids; while simultaneously reducing reliance on chemical pesticides. The objective of this study was to evaluate a multi-parent advanced generation inter-cross (MAGIC) population of cowpea against aphids, across cowpea growing regions in Uganda. The study was arranged in alpha lattice design, with two replicates in three locations over two seasons (2018B and 2019A). Results revealed significant effects (P<0.001) for the main treatment effects, genotype x location and location x season interaction for both infestation and damage. The genotype x season interaction was significant (P<0.01) for both aphid infestation and damage; while the three-way interaction was only significant (P<0.001) for aphid infestation, but not for damage. The study identified five new resistant and stable genotypes from the MAGIC panel, including MAGIC131, MAGIC-132, MAGIC149, MAGIC170 and MAGIC280; and one resistant parent, SUVITA-2. The study further revealed MAGIC-125, MAGIC-171, MAGIC153, MAGIC-333, MAGIC177, MAGIC-292, MAGIC282, MAGIC249, MAGIC162, SEC 4W * SEC 5T, NAROCOWPEA 4, MAGIC-204, MAGIC-039, MAGIC060, MAGIC-097, NAROCOWPEA 3, MAGIC-233, MAGIC090 and MU 9 to be moderately resistant and high yielding genotypes. The above genotypes are recommended for use in the cowpea breeding programme, to develop improved resistant lines against aphids in Uganda

Identification of common bean genotypes with dual leaf and pod resistance to common bacterial blight disease in Uganda

Common Bacterial Blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), is a serious disease that affects common bean production worldwide. In Uganda, it is the most severe and widely occurring bacterial disease, causing significant yield losses in common bean. Although various sources of resistance have been developed around the world, none of the varieties grown in Uganda is known to be resistant. The objective of this study was to identify lines with combined leaf and pod resistance for introgression into locally adapted but susceptible Ugandan genotypes. A total of 132 common bean accessions was evaluated in a screenhouse and under field conditions, in an 11x12 alpha lattice design. Genotypes were inoculated with a local isolate in a screenhouse; while the plants were left to undergo natural infestation in field. Results indicated significant differences (P&lt;0.001) in genotypic reactions against the CBB disease, with a range of disease scores of 2.2 - 7.8 on leaves and 2.6 - 7.1 on pods (1-9 CIAT disease scale), suggesting high genetic variability among the tested germplasm. Relatively low correlation (r = 0.39) was observed between leaf and pod reactions, suggesting differential expression of CBB resistance in these two plant organs. Overall, four genotypes, NE2-14-8, NE17-14-29, NE14-09-78 and VAX3, consistently showed resistance in both screenhouse and field evaluations, leaf and pod inoculations and at all sampling stages. These genotypes were, therefore, identified for transferring CBB resistance into Ugandan susceptible market class bean varieties.Le fl\ue9trissement bact\ue9rien commun (CBB) caus\ue9 par Xanthomonas campestris pv. phaseoli (Xcp) et Xanthomonas spp. var. fuscans (Xcpf) est une s\ue9rieuse maladie qui affecte, de fa\ue7on globale, la production du haricot commun. En Ouganda, elle est, de loin, la maladie bact\ue9rienne la plus s\ue9v\ue8re et vastement r\ue9pandue causant de pertes significatives au rendement du haricot commun. Malgr\ue9 que de nombreuses sources de r\ue9sistance aient \ue9t\ue9 d\ue9velopp\ue9es dans le monde, aucune des vari\ue9t\ue9s cultiv\ue9es en Ouganda n\u2019est connue \ueatre r\ue9sistante. L\u2019objectif de cette \ue9tude \ue9tait d\u2019identifier des lignes \ue0 r\ue9sistance combin\ue9e des feuilles et gousses pour son introgression dans les vari\ue9t\ue9s locales adapt\ue9es mais susceptibles. Au total, 132 accessions de haricot commun \ue9taient \ue9valu\ue9es sous serre et dans le champ dans un dispositif experimental alpha-lattice 11x12. Les g\ue9notypes \ue9taient inocul\ue9s sous serre par un isolat local pendant que l\u2019infestation \ue9tait naturelle dans le champ. Les r\ue9sultats montrent de diff\ue9rences hautement significatives dans la r\ue9action des g\ue9notypes face \ue0 la maladie CBB avec des scores variant de 2,2 \ue0 7,8 sur les feuilles et de 2.6 \ue0 7.1 sur les gousses (l\u2019\ue9chelle 1-9 de CIAT) indiquant une forte variabilt\ue9 g\ue9n\ue9tique au sein du germoplasm test\ue9. Une corr\ue9lation relativement faible (r = 0.39) \ue9tait observ\ue9e entre la r\ue9action des feuilles et celle des gousses sugg\ue9rant une expression diff\ue9rentielle de la r\ue9sistance \ue0 la maladie CBB dans ces deux organes de la plante. De fa\ue7on g\ue9n\ue9rale, quatre g\ue9notypes NE2-14-8, NE17-14-29, NE14-09-78 and VAX3 ont \ue9t\ue9, de fa\ue7on constante, r\ue9sistants aux \ue9valuations sous serre et dans le champ, aux inoculations des feuilles et des gousses et durant toute la p\ue9riode de mesure. Ces g\ue9notypes \ue9taient donc identifi\ue9s pour le transfert de la r\ue9sistance dans les vari\ue9t\ue9s locales susceptibles d\u2019Ouganda

Genetic Variability and Evolutionary Implications of RNA Silencing Suppressor Genes in RNA1 of Sweet Potato Chlorotic Stunt Virus Isolates Infecting Sweetpotato and Related Wild Species

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