Genetic homogeneity among Ugandan isolates of Xanthomonas campestris pv. musacearum revealed by randomly amplified polymorphic DNA analysis

The Random Amplification of Polymorphic DNA (RAPD) analysis was used to detect the genetic diversity among Ugandan isolates of Xanthomonas campestris pv. musacearum (Xcm), the causal agent of banana Xanthomonas wilt (BXW) disease. Seven random primers were used because of their ability to amplify reproducible and reliable fingerprints generated between 6 - 12 amplicons each from the Xcm isolates obtained from central core of pseudostems, peduncles, fruit peelings, sap, nectar,insects’ bodies and bacterial oozes. Regardless of the source and geographical origin, similar fingerprints were generated from the tested isolates. Using a similarity coefficient of 58%, the unweighted pair group method with arithmetic averaging (UPGMA) analysis did not reveal anysignificant differences in clustering, with exception of a single isolate that had unique fingerprints. Prior to the genetic analysis, all the isolates compared showed no significant difference (P = 0.92) with regardto incubation period for appearance of symptoms and the severity of symptoms in pathogenicity test. Thus, our data indicates that the population of Xcm in Uganda is clonal, that is, one uniform populationbeing spread fast and efficiently, suggesting that there is a low likelihood of the current population to rapidly evolve, in the near future, into more virulent strains to overcome any resistance deployed

The survival of Xanthomonas Campestris PV.musacearum in soil and plant debris

No Abstract

Spatial and temporal distribution of insect vectors of Xanthomonas campestris pv. musacearum and their activity across banana cultivars grown in Rwanda.

Insect vectors of Xanthomonas campestris pv musacearum (Xcm) have played a major role in long distance and plant to plant transmission of Xanthomonas wilt of banana (XW). The prevalence of insects has been reported to vary in space and time. Some banana cultivars have also been reported to attract more insect vectors of Xcm than others. The present study was conducted to determine the spatial and temporal distribution of insect vectors of Xcm and assess their activity across banana cultivars grown in Rwanda. The study was carried out in four banana growing areas of Rwanda selected on the basis of their altitude (i.e.Low, Medium and High). The Kivu Lake Border region was selected as a fourth site due to the high prevalence of XW. Insects were sampled in the four annual seasons (short dry, short rainy, long dry and long rainy) and at different times of the day. During sampling of insects, the incidence of XW-male bud infection was also recorded. Collected insects were immediately sorted into taxonomic groups and conserved in vials containing 70% ethanol for further identification to genus and species level. Five insect specimens in each taxon were put aside for the isolation of Xcm on their external body parts. There was a high prevalence of fruit flies, honey bees and other flies (in other families than Drosophilidae and Tephritidae) compared with wasps, ants and beetles. More insects were recorded in the low altitude area and during the long rainy season. These findings correlated with the observed high incidence of XW in the wet seasons. Incidence of floral infections was higher in the low altitudes declining with the increase in altitude, correlating with the decline in insect activity as altitude increased. The activity of insects on banana male buds varied among banana cultivars, with more activity on beer (AAA-East African Highland (EAH) and ABB types) and dessert banana cultivars compared with cooking or mixed use cultivars. Among the cooking types only ‘Injagi’ and its clone sets ‘Barabeshya’ and ‘Incakara’ attracted large insect populations. Banana cultivars ‘Nkazikamwe’ (cooking AAA-EAH), ‘Impura’ (beer AAAEAH) and ‘Ikinyangurube’ (dessert AAA) possessed persistent male bracts and neuter flowers and were less attractive to flower visitors. These cultivars could be promoted in areas prone to insect vector infections. Timely and proper de-budding should be emphasized with special attention during the rainy seasons and for banana cultivars with non-persistent male buds

Studies of the genetics of inheritance of stem rust resistance in bread wheat

Pgt race TTKSK (Ug99) has a wide virulence range with respect to currently grown wheat cultivars worldwide. Aspects of migration, mutation, recombination and selection in the pathogen have led to previously deployed stem rust resistance genes being ineffective. Race TTKSK has further evolved to acquire virulence for resistance genes such as Sr24 (race Ug99 + Sr24) and Sr36 (Ug99 + Sr36). Five resistant wheat lines (KSL-2, KSL-3, KSL-5, KSL-12 and KSL-19) which were resistant in tests during 2008, 2009 and 2010 were used as parents in crosses with stem rust susceptible line CACUKE to develop genetic populations for determining the inheritance of resistance to stem rust. F3 populations were evaluated at KARI Njoro in the 2012 off season and 2012 to 2013 main season. The adult plant stem rust responses were scored using the modified Cobb’s scale. The F2:3 lines of population(s) exhibiting qualitative variation were grouped as homozygous resistant (HR), segregating (Seg) and homozygous susceptible (HS). Heavy disease pressure was present during the cropping seasons with the check CACUKE displaying 90% susceptibility. Chi square analysis revealed that the segregation data in the parent KSL-2 did not deviate significantly from the single gene model (1:2:1) suggesting that the resistance to stem rust is conditioned by a single dominant gene. The Chi square test also revealed that the stem rust resistance in the parents KSL-3, KSL-5, KSL-12 and KSL-19 was conditioned by two genes. The families from the KSL-2 and KSL-3 crosses also segregated for the presence of the pseudo black chaff implying that the Sr2 gene could be present in the background of these wheat parents. The superior transgressive segregants identified in these crosses will be used in breeding.Keywords: Genetic, wheat, gene, resistanceAfrican Journal of Biotechnology Vol. 12(21), pp. 3153-315

Variation in nectar volume and sugar content in male flowers of Musa cultivars grown in Rwanda and their non-effect on the numbers of visiting key diurnal insect vectors of banana Xanthomonas wilt

Insects are a major mode of banana Xanthomonas wilt (XW) spread. High insect activity has been blamed for the high XW incidence in ‘Kayinja’ (ABB-genome) dominated banana landscapes across east and central Africa. ‘Kayinja’ male bud nectar composition reportedly contributes to high insect activity. The variation in nectar composition with agro-ecological zones and banana cultivars and its influence on the number of visiting insects in Rwanda were assessed. Three male buds were collected per cultivar for nectar extraction and analysis using a high performance liquid chromatography. Nectar volume and sugar concentrations varied (P<0.001) across 27 banana cultivars, annual seasons and agro-ecological zone. The highest nectar volume was recorded among the East African highland cooking cultivars (AAA-genome) in the high altitude site and the short-heavy rainy season. Nectar contained three sugars: glucose, fructose and sucrose, though hexose (glucose and fructose) was dominant. The three sugars varied significantly (P<0.001) within each cultivar. The total nectar-sugar concentration ranged from 2.3–32%, with the highest among dessert cultivars ‘Kamaramasenge’ (AAB-genome) and ‘Gisukari’ (AAA-genome). No strong correlation occurred between insect population and total nectar sugar concentration or nectar volume. Insect populations were rather influenced by the weather conditions, the long rainy season characterized by moderate well distributed rainfall recording the highest insect populations as compared to the short rainy season (with heavy rainfall) and the dry seasons

Prevalence of viruses infecting cowpea in Uganda and their molecular detection

The main areas for cowpea cultivation in Uganda were surveyed in June and October 2006 for viruses affecting the crop. Seed and leaf samples from symptomatic and asymptomatic plants were collected from farmers’ fields and analysed for infecting viruses using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). The viruses detected in the leaf and seed samples were: cucumber mosaic cucumovirus (CMV), cowpea mild mottle calarvirus (CPMMV), cowpea mottle carmovirus (CPMoV), Cowpea chlorotic mottle bromovirus (CCMV), Cowpea yellow mosaic comovirus (CYMV), cowpea severe mosaic comovirus (CPSMV), cowpea aphid-borne mosaic potyvirus (CABMV) and Southern bean mosaic sobemovirus (SBMV). CPMV was detected only in leaf samples. CMV and CABMV were later confirmed using reverse transcription polymerase chain reaction (RT-PCR). Of the viruses detected in leaf samples, 53.26% occurred as single infections, 24.46% dual and 22.28% multiple infections. Similarly, analysis of seed samples revealed infection of 40.6, 34.6 and 24.8% for single, dual and multiple infections, respectively. Multiple virus infections were associated with more disease severity and higher yield losses. The seed transmission levels of 23.0, 20.3 and 16.4% were recorded for CMV, CPMMV and CABMV, respectively. This study identified six more viruses in addition to what was previously reported in the country, of which eight were seed-borne. This necessitates the need for the production and use of virus-free seeds, development of virus resistant genotypes and adoption of efficient seed certification systems.Keywords: Vigna unguiculata, disease incidence, seed-borne viruses, ELISA, (RT-PCR

Distribution of common bacterial blight disease under different agroecologies in Uganda

Common bacterial blight disease (CBB) causes severe yield and seed quality losses on common bean worldwide. Information about CBB distribution is important in designing effective control strategies. This disease has been managed using intergraded strategies, involving use of certified seed produced in areas of low disease pressure. Unfortunately, areas of low CBB pressure have not been mapped in Uganda. This study was conducted to determine the distribution and intensity of CBB in Uganda, in order to establish low pressure areas for multiplication of clean certified seed. A survey was conducted in farmers\u2019 fields in18 locations found in four rainfalls-based agroecology in Uganda, for two seasons of 2016. The Victoria Cresent and Mbale farmland had the highest disease intensity index (29%); followed by Central woodland savannah (21%). The Northwest farm land and South west grass farm lands had low CBB intensity index of 2.5 and 7.8%, respectively. Thus, The Northwest farm land (Arua, Amuru, Nwoya) and South west grass farm lands (Rakai, Ntungamo Lwengo and Bukomansimbi), are recommended for production of CBB free bean seeds.La maladie bact\ue9rienne commune (MBC) provoque de graves pertes de rendement et de qualit\ue9 des semences de haricot commun dans le monde entier. Les informations sur la distribution du MBC sont importantes pour la conception de strat\ue9gies de contr\uf4le efficaces. Cette maladie a \ue9t\ue9 g\ue9r\ue9e \ue0 l\u2019aide de strat\ue9gies intercal\ue9es, impliquant l\u2019utilisation de semences certifi\ue9es produites dans des zones de faible pression de la maladie. Malheureusement, les zones de faible pression du CBB n\u2019ont pas \ue9t\ue9 cartographi\ue9es en Ouganda. Cette \ue9tude a \ue9t\ue9 faite pour d\ue9terminer la distribution et l\u2019intensit\ue9 du CBB en Ouganda, afin d\u2019\ue9tablir des zones de basse pression pour la multiplication de semences certifies qui sont propres. Une enqu\ueate a \ue9t\ue9 faite dans les champs d\u2019agriculteurs dans 18 localit\ue9s situ\ue9es dans quatre agro\ue9cologies en Ouganda bas\ue9es sur les pr\ue9cipitations, pendant les deux saisons de 2016. Les terres agricoles de Victoria Cresent et de Mbale pr\ue9sentaient l\u2019indice d\u2019intensit\ue9 de maladie le plus \ue9lev\ue9 (29%); suivi de la savane bois\ue9e centrale (21%). Les terres agricoles du nord-ouest et celles du sud-ouest avaient un indice d\u2019intensit\ue9 de CBB faible de 2,5 et 7,8%, respectivement. Ainsi, les terres agricoles du Nord-Ouest (Arua, Amuru, Nwoya) et celles du Sud-Ouest (Rakai, Ntungamo Lwengo et Bukomansimbi) sont recommand\ue9es pour la production de semences de haricot exemptes de CBB

Evaluation of tomato genotypes for tolerance to major diseases in Uganda

Tomato ( Solanum lycopersicum L.) is a priority vegetable in Uganda, but due to its limited genetic base, its cultivated types are prone to a variety of diseases. The objective of this study was to evaluate new tomato genotypes for resistance to major tomato diseases under hotspot conditions in Uganda. Fourty-five tomato genotypes were evaluated for reactions to tomato bacterial wilt, tomato bacterial speck, early blight and late blight. The study was conducted for two rainy seasons in 2019, at the National Crops Resources Research Institute, Namulonge in Uganda. Data for severity and incidence were collected at two-week intervals after transplanting. Twelve genotypes (Nouvella F1, Rambo F1, Commando F1, AVTO1315, AVTO922, AVTO1701, AVTO1219, AVTO1464, MT56, ADV1287A, Pruna and Vega) exhibited high levels of tolerance to bacterial wilt; while bacterial speck presented mild symptoms majorly seen on Vega, Zodiac and AVTO9802. Rhino, AVTO1418, AVTO1314, Eureka, Roma VFN, MT56, Pinktop, Assila F1, Money-maker, AVTO0922 and AVTO1464 were the least affected by early blight; while AVTO1219, AVTO1701, ADV12021, ADV12076 and ADV1287A expressed low AUDPC values for late blight. Overall, AVTO1315 was the best yielder (30.8 metric tonnes ha-1), followed by AVTO0301 (29.0 t ha-1) and Nouvella F1 (26.1 t ha-1). Among the tomato genotypes evaluated, we recommend AVTO1701, AVTO0922, AVTO1464, AVTO0301 AVTO1315, AVTO1219, Pruna, Vega, ADV1287A and MT56 for the national performance trials.La tomate ( Solanum lycopersicum L.) est un l\ue9gume prioritaire en Ouganda, mais en raison de sa base g\ue9n\ue9tique limit\ue9e, ses types cultiv\ue9s sont sujets \ue0 une vari\ue9t\ue9 de maladies. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer des g\ue9notypes de tomates s\ue9lectionn\ue9s pour leur r\ue9sistance aux principales maladies de la tomate dans des conditions de hotspot en Ouganda. Quarante-cinq g\ue9notypes de tomates ont \ue9t\ue9 \ue9valu\ue9s pour leurs r\ue9actions au fl\ue9trissement bact\ue9rien de la tomate, \ue0 la tache bact\ue9rienne de la tomate, au mildiou et au mildiou. L\u2019\ue9tude a \ue9t\ue9 men\ue9e pendant deux saisons des pluies en 2019, au National Crops Resources Research Institute, \ue0 Namulonge en Ouganda. Les donn\ue9es de gravit\ue9 et d\u2019incidence ont \ue9t\ue9 recueillies \ue0 des intervalles de deux semaines apr\ue8s la transplantation. Douze g\ue9notypes (Nouvella F1, Rambo F1, Commando F1, AVTO1315, AVTO922, AVTO1701, AVTO1219, AVTO1464, MT56, ADV1287A, Pruna et Vega) pr\ue9sentaient des niveaux \ue9lev\ue9s de tol\ue9rance au fl\ue9trissement bact\ue9rien; tandis que la tache bact\ue9rienne pr\ue9sentait des sympt\uf4mes b\ue9nins principalement observ\ue9s sur Vega, Zodiac et AVTO9802. Rhino, AVTO1418, AVTO1314, Eureka, Roma VFN, MT56, Pinktop, Assila F1, Money-maker, AVTO0922 et AVTO1464 ont \ue9t\ue9 les moins touch\ue9s par le mildiou; tandis que AVTO1219, AVTO1701, ADV12021, ADV12076 et ADV1287A ont exprim\ue9 de faibles valeurs AUDPC pour le mildiou. Dans l\u2019ensemble, AVTO1315 a \ue9t\ue9 le meilleur producteur (30,8 tonnes m\ue9triques ha-1), suivi par AVTO0301 (29,0 t ha-1) et Nouvella F1 (26,1 t ha-1). Parmi les g\ue9notypes de tomates \ue9valu\ue9s, nous recommandons AVTO1701, AVTO0922, AVTO1464, AVTO0301 AVTO1315, AVTO1219, Pruna, Vega, ADV1287A et MT56 pour les essais de performance nationaux

INHERITANCE OF ROOT DRY MATTER CONTENT IN SWEETPOTATO

There has been much emphasis on breeding for increased sweetpotato storage root yield, but less on dry matter yield, and its inheritance. High dry matter content (DMC) is associated with consumer preferences, and is important for the processing industry. This study was conducted to determine the type of gene action controlling DMC and to assess genotype by environment (G x E) interaction effect on DMC in sweetpotato. Five parental clones varying in DMC were hand-crossed in a half-diallel design to generate ten families. Ten genotypes of each family were planted in a trial at Namulonge (swamp and upland environments) and Serere in Uganda in 2009 and 2010. Highly significant (P&lt;0.001) differences were found both between genotypes and between families for DMC. High significant general combining ability (GCA) (P&lt;0.001) and specific combining ability (SCA) (P&lt;0.01) were obtained, meaning that the differences among families for high DMC were due to both GCA and SCA. The relative importance of GCA and SCA was 0.59, indicating that additive gene action was slightly more predominant than non-additive gene action in predicting progeny performance for high DMC. Broad sense heritability (H) estimates for DMC were 0.70 and 0.73, respectively on genotype and family means across environments basis, suggesting that DMC was moderately influenced by the environment. Rapid selection for best genotypes would be possible, since progenies can be predicted from the phenotype of the parents. Parent SPK (GCA = 1.02) was the best combiner. The effect of location was less significant compared to seasons, suggesting the need to evaluate genotypes for several seasons, but in few locations to save resources.Plusieurs efforts ont \ue9t\ue9 fournis dans le cadre d\u2019augmenter le rendement de la patate douce, mais peu d\u2019efforts visant le rendement sec et son h\ue9ritabilit\ue9. La mati\ue8re s\ue8che est associ\ue9e aux pr\ue9f\ue9rences des consommateurs et elle est importante dans l\u2019industrie de transformation. Cette \ue9tude a \ue9t\ue9 men\ue9e dans le but de d\ue9terminer le type de l\u2019action g\ue9n\ue9tique contr\uf4lant la mati\ue8re s\ue8che, ainsi que d\u2019\ue9valuer l\u2019effet d\u2019interaction g\ue9notype x environnement sur la mati\ue8re s\ue8che sur la patate douce. Cinq diff\ue9rents parents en terme de mati\ue8re s\ue8che ont \ue9t\ue9 crois\ue9s en moiti\ue9 diall\ue8le et dix familles sont obtenues. Les semences sont plant\ue9es dans les boites en bois dans les serres \ue0 Namulonge, Uganda. Dix g\ue9notypes pour chacune des familles sont plant\ue9es dans l\u2019essai \ue0 Namulonge (environnement marrais et hautes terres) et Serere en bloques compl\ue8tement randomis\ue9es, avec deux r\ue9p\ue9titions, durant la p\ue9riode Octobre 2009-Mars 2010. Pour d\ue9terminer la mati\ue8re s\ue8che, une quantit\ue9 de 200 g pour chacune des g\ue9notypes a \ue9t\ue9 s\ue9ch\ue9e \ue0 650C jusqu\u2019\ue0 ce que le poids soit constant. Les donn\ue9es sont analys\ue9es en utilisant le logiciel Genstat. Aptitude g\ue9n\ue9rale \ue0 la combinaison (AGC) et aptitude sp\ue9cifique \ue0 la combinaison (ASC) sont calcul\ue9es selon Mod\ue8le I, M\ue9thode 4 selon la description de Griffing (1956). Hautes significative (P&lt; 0,001) diff\ue9rences sont trouv\ue9es aussi bien entre g\ue9notypes que familles pour la mati\ue8re s\ue8che. Hautes significatives AGC (P&lt;0,001) et ASC (P&lt;0,01) sont trouv\ue9es, signifiant que les diff\ue9rences observ\ue9es entre les familles pour la mati\ue8re s\ue8che sont dues \ue0 la fois \ue0 AGC et ASC. L\u2019importance relative de l\u2019AGC et ASC \ue9tait 0,59, ce qui indique que l\u2019action g\ue9n\ue9tique additive \ue9tait un peu plus importante que l\u2019action g\ue9n\ue9tique non-additive en pr\ue9dicant la performance des prog\ue9nitures pour la mati\ue8re s\ue8che. L\u2019h\ue9ritabilit\ue9 en large sens (H) pour la mati\ue8re s\ue8che \ue9tait de 0,70 et 0,73 en se basant respectivement sur la moyenne du g\ue9notype et celle de la famille sur tous les environnements, sugg\ue9rant que la mati\ue8re s\ue8che \ue9tait mod\ue9r\ue9ment influenc\ue9e par l\u2019environnement. Ceci indique que la s\ue9lection rapide des g\ue9notypes serait possible, car les prog\ue9nitures peuvent \ueatre pr\ue9venues en se basant sur le ph\ue9notype des parents. Parent SPK (GCA=1,02) \ue9tait la meilleure combinant dans cette \ue9tude. L\u2019effet des locations \ue9tait moins significatif comparable aux saisons, sugg\ue9rant l\u2019importance d\u2019\ue9valuer les g\ue9notypes sur plusieurs saisons, mais dans les moins de locations dans le cadre d\u2019\ue9conomiser les ressources

Pathogenicity and virulence of Ugandan isolates of common bacterial blight disease pathogen ( Xanthomonas spp.)

Breeding for resistance is a major component in the integrated management of common bacterial disease of beans ( Phaseolus vulgaris L.). Use of less virulent strains or strains with attenuated virulence may lead to selection of resistant genotypes with intermediate response, when exposed to more virulent strains of the pathogen. The objective of this study to identify and characterise Ugandan isolates of common bacterial blight disease-causing pathogens for virulence. Bacteria were isolated from leaf samples collected from districts of Kabale, Masaka, Bukomansimbi, Mubende, Mbale, Bulambuli and Apac, all in Uganda, during the first season of 2016. The bacteria were tested for pathogenicity, as well as virulence on both breeding and local varieties. The study identified three most virulent isolates, namely MBL020, KAB-3 and BUL-14, all belonging to Xathomonas citri pv fuscans. These isolates are very similar to those previously identified from Uganda (NCPB 670 and NCCPB 1402) more than 50 years ago. The study further revealed that NAROBEAN1, NAROBEAN 2, NAROBEAN 4, VAX 3, VAX5 and NE 2- 14- 8 had better resistance compared to other tested genotypes.La s\ue9lection pour la r\ue9sistance est un \ue9l\ue9ment majeur de la gestion int\ue9gr\ue9e des maladies bact\ue9riennes courantes des haricots ( Phaseolus vulgaris L.). L\u2019utilisation de souches moins virulentes ou de souches \ue0 virulence att\ue9nu\ue9e peut conduire \ue0 la s\ue9lection de g\ue9notypes r\ue9sistants \ue0 r\ue9ponse interm\ue9diaire, lorsqu\u2019ils sont expos\ue9s \ue0 des souches plus virulentes du pathog\ue8ne. L\u2019objectif de cette \ue9tude etait d\u2019identifier et de caract\ue9riser les isolats ougandais de pathog\ue8nes causant la maladie bact\ue9rienne commune pour la virulence. Des bact\ue9ries ont \ue9t\ue9 isol\ue9es \ue0 partir d\u2019\ue9chantillons de feuilles pr\ue9lev\ue9s dans les districts de Kabale, Masaka, Bukomansimbi, Mubende, Mbale, Bulambuli et Apac, tous en Ouganda, au cours de la premi\ue8re saison de 2016. Les bact\ue9ries ont \ue9t\ue9 test\ue9es pour leur pathog\ue9nicit\ue9, ainsi que leur virulence \ue0 la fois pour la reproduction et vari\ue9t\ue9s locales. L\u2019\ue9tude a identifi\ue9 les trois isolats les plus virulents, \ue0 savoir MBL020, KAB-3 et BUL-14, tous appartenant \ue0 Xathomonas citri pv fuscans. Ces isolats sont tr\ue8s similaires \ue0 ceux pr\ue9c\ue9demment identifi\ue9s en Ouganda (NCPB 670 et NCCPB 1402), il y a plus de 50 ans. L\u2019\ue9tude a en outre r\ue9v\ue9l\ue9 que NAROBEAN1, NAROBEAN 2, NAROBEAN 4, VAX 3, VAX5 et NE 2- 14-8 avaient une meilleure r\ue9sistance par rapport aux autres g\ue9notypes test\ue9s