Prevalence and Implications of Sweetpotato Recovery From Sweet Potato Virus Disease in Uganda

Sweet potato virus disease (SPVD) is the most important disease of sweetpotato in the tropics. It causes yield losses of up to 98% and extinction of elite cultivars. Although there are no reports of immune cultivars, disease recovery phenomenon (a manifestation of some form of resistance) was reported in many vegetatively propagated crops including sweetpotato. A total of 1320 sweetpotato cultivars from 3 major sweetpotato growing regions in Uganda were field evaluated for SPVD severity, of which 24% showed recovery from SPVD. The nature of SPVD recovery was assessed in the screenhouse using 20 distinct cultivars after graft inoculation with SPCSV and SPFMV, the SPVD causing viruses. SPVD progress in 20 graft inoculated cultivars was significantly (P<0.05) different; Munyeera was the most resistant cultivar followed by New Kawogo and Polyster. The 3 resistant cultivars (disease score 1-2) displayed recovery from SPVD which was correlated with a reduction in SPFMV titers as observed from quantitative ELISA. Reversion was not evident since all cuttings taken from recovered vine tips later tested positive for both viruses. Cultivars with the ability to recover were common in farmers' fields in central (36.4%) and western (33.3%) regions of Uganda, which are high SPVD pressure zones. Conversely, fewer cultivars (5.6%) from the low disease pressure eastern region displayed recovery. The very susceptible cultivars (disease score of 4-5) were not prevalent in central and western regions. These observations suggest that SPVD recovery has an influence on the cultivars grown in different SPVD pressure zones, where more susceptible cultivars are preferred in areas of low disease pressure.La maladie de virus de la patate douce (SPVD) est une maladie la plus importante de la patate douce dans les tropiques. Elle provoque des pertes de production allant jusqu'\ue0 98 % et voir m\ueame l'extinction des cultivars d'\ue9lite. Bien qu'il n'ya pas de rapports sur les cultivars r\ue9sistants, le ph\ue9nom\ue8ne de r\ue9couvrement contre la maladie (manifestation de quelques formes de r\ue9sistance) \ue9tait signal\ue9 dans beaucoup de cultures v\ue9g\ue9tativement propag\ue9es dont la patate douce. Au total 1320 cultivars de patate douce provenant de 3 grandes r\ue9gions cultivatrices de la culture en Ouganda \ue9taient \ue9valu\ue9s au champs pour la s\ue9v\ue9rit\ue9 en SPVD parmi lesquels 24% ont montr\ue9 une r\ue9sistance \ue0 la SPVD. La nature de la r\ue9sistance au SPVD \ue9tait \ue9valu\ue9e en serre utilisant 20 diff\ue9rents cultivars apr\ue8s inoculation de la greffe avec SPCSV et SPFMV, les SPVD causant les virus. Le progr\ue8s de la SPVD dans 20 greffes innocul\ue9es \ue9tait significativement (P<0.05) diff\ue9rent; Munyeera \ue9tait le cultivar le plus r\ue9sistant suivi de New Kawogo et Polyster. Les 3 cultivars r\ue9sistants (score de maladie: 1-2) ont montr\ue9 un r\ue9couvrement de SPVD correl\ue9 avec une r\ue9duction dans les titres de SPFMV comme observ\ue9 dans l'enzyme quantitatif ELISA. La r\ue9version n'\ue9tait pas \ue9vidente depuis que toutes les bout\ufbres prises des cultivars r\ue9sistants \ue9taient finalement infect\ue9es par les virus SPCSVet SPFMV. Les cultivars ayant la capacit\ue9 de se r\ue9tablir du virus \ue9taient commun dans les champs de fermiers dans les r\ue9gions centrale (36.4%) et ouest ( 33.3%) de l'Ouganda, qui \ue9taient des zones sous pression \ue9lev\ue9e de SPVD. Au contraire, tr\ue8s peu de cultivars (5,6%) provenant de la r\ue9gion east \ue0 niveau bas de pression de maladie ont manifest\ue9 un r\ue9tablissement. Les cultivars les plus susceptibles (score de maladie: 4-5) n'\ue9taient pas pr\ue9valents dans les r\ue9gions centrale et ouest. Ces observations sugg\ue8rent que le r\ue9couvrement de la patate contre le SPVD a une influence sur les cultivars cultiv\ue9s dans diff\ue9rentes zones de pression sous SPVD o\uf9 plus de cultivars susceptibles sont pr\ue9f\ue9r\ue9s dans des milieux \ue0 basse pression de maladie

Occurrence of rice yellow mottle virus resistance breaking isolates in lowland catchment zones of Uganda

Rice (Oryza spp; 2n=24.) production in Uganda and Africa in general, is seriously threatened by the Rice yellow mottle virus disease (RYMVD), a disease caused by Rice yellow mottle virus (RYMV) within the genus Sobemovirus; family Sobemoviridae. This study investigated the existence and distribution of resistance-breaking RYMV pathotype in the three major lowland rice catchment areas in Uganda. Four known rice accessions resistant to Rice yellow mottle virus (RYMV) namely; Gigante, Tog5672, Tog5674 and Tog5681, carrying resistant allele’s rymv1-2, rymv1-4 & RYMV3, rymv1-5 and rymv1-3, respectively, were tested for their response to different RYMV isolates. The isolates were collected from three major lowland rice catchment areas of Doho, Kibimba, and Olweny in Uganda. Out of 100 leaf samples collected from the field and assayed for RYMV and confirmed to be positive using RT-PCR, 83 isolates induced symptoms on IR64- the RYMV susceptible line. Seventy-seven (92.8%) isolates were able to overcome resistance in at least one of the four differential rice accessions, as confirmed by the presence of RYMV symptoms; while 6 (7.2%) isolates were asymptomatic. Variation in time (days) for symptom development post-inoculation (dpi) and AUDPC were observed. Symptoms appeared within 5-7 days on IR64; while it took on average 11, 18, 36, and 18 days to appear on Gigante, Tog5672, Tog5674 and Tog5681, respectively. The highest AUDPC was observed on IR64 (254.7); while the lowest was observed on Tog5681 (74.1). Two major patho-groups were observed; those that broke down resistance in Gigante only (25.3%) and Gigante & Tog5672 (33.7%). Five isolates from Doho (Budaka & Bugiri districts) and Kibimba (Butaleja district) catchment areas broke down RYMV resistance in three accessions i.e. (Tog5681, Gigante & Tog5672) and (Tog5674, Gigante & Tog5672), respectively. Resistance breaking isolates were confirmed in all  the three sampled catchment zones, however, Doho and Kibimba had some unique isolates that broke down resistance in accessions carrying resistance allele rymv 1-3 and rymv1-5 in addition to rymv1-2. Results from this study showed that RYMV isolates in Uganda can break down resistance conferred by the rymv1-2 resistance gene allele. However, accessions Tog5681 and Tog5674 seem to hold stable RYMV resistance and, thus are recommended for RYMV breeding

BANANA JUICE AS AN ALTERNATIVE ENERGY SOURCE FOR BANANA IN VITRO GROWTH MEDIUM

Energy sources in tissue culture media are important for plants whose photosynthetic efficiency is insufficient under in vitro conditions. However, the cost of tissue culture grade energy sources is high, thus making tissue culture derived plantlets expensive. The cost of table sugar commonly used in commercial tissue culture laboratories and a substitute for tissue culture grade sucrose in Uganda, is also relatively high given the volumes used. The aim of this study was to evaluate the possibility of exploiting banana ( Musa spp.) juice, as an energy source in place of table sugar or tissue culture grade sucrose. Banana juice was extracted from the locally available East African Highland Banana (EAHB) beer cultivars, Mbidde-Kabula, Pisang awak (Kayinja) and Km 5, and used at levels of 20, 30, 40 and 50 ml l-1. The quality and amount of juice necessary to support in vitro growth of cooking EAHB cultivars Nakabululu, Nakitembe and Nakinyika was evaluated. The juice had varied composition of salts, sugars and organic acids; but with pH compared with table sugar solution. The highest number of shoots and shoot height was observed when bananas were cultured on media supplemented with 50 ml l-1 Kayinja juice. This response was greater than that observed with culture media supplemented with the control energy source of 30 g l-1 of table sugar. Results also showed that banana juice not only enhanced micropropagation but also improved in vitro plantlet vigour and reduced the cost of energy sources by 30%.Les sources d\u2019\ue9nergies sont importantes dans les milieux de culture in-vitro des plantes dont l\u2019efficacit\ue9 photosynth\ue9tique est insuffisante dans les conditions de culture in-vitro . Cependant, le co\ufbt des sources d\u2019\ue9nergies utilis\ue9es en culture in-vitro de tissus est \ue9lev\ue9, ceci rend couteux les plantules produites par culture in-vitro. Le co\ufbt du sucre de table habituellement utilis\ue9 dans les laboratoires commerciaux de culture de tissus in-vitro ainsi que celui du substitut de sucrose utilis\ue9 en Ouganda reste relativement \ue9lev\ue9, \ue9tant donn\ue9 les volumes utilis\ue9s. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer la possibilit\ue9 d\u2019exploiter le suc de bananier ( Musa spp.), comme une source d\u2019\ue9nergie en lieu et place du sucre de table ou du sucrose. Le suc de bananier a \ue9t\ue9 extrait des vari\ue9t\ue9s de bananier localement disponible\ua0; bananier de terre ferme de l\u2019Afrique de l\u2019Est (EAHB), Mbidde-Kabula, Pisang awak (Kayinja) and Km 5, et utilis\ue9 \ue0 diff\ue9rentes concentrations telles que 20, 30, 40 and 50 ml l-1. La qualit\ue9 et la quantit\ue9 de suc n\ue9cessaire pour assurer la croissance in-vitro des vari\ue9t\ue9s EAHB, Nakabululu, Nakitembe and Nakinyika a \ue9t\ue9 \ue9valu\ue9. Le suc avait des concentrations vari\ue9es en sels, sucres et acides organiques; mais avec un pH comparable \ue0 celui du sucre de table en solution. Le plus grand nombre de rejetons et les pousses les plus hautes ont \ue9t\ue9 obtenues lorsque les tissus du bananier sont cultiv\ue9s dans un milieu contenant 50 ml l-1 de suc de Kayinja. Cette r\ue9ponse \ue9tait plus \ue9lev\ue9e que celle obtenue avec culture sur un milieu t\ue9moin (30 g l-1 de sucre de table). Les r\ue9sultats indiquent que le suc de bananier au-del\ue0 de renforcer la micro propagation, am\ue9liore aussi la vigueur des plantules en verre et r\ue9duit de 30% le co\ufbt des sources d\u2019\ue9nergies utilis\ue9es en culture de tissus in-vitro

Morphotypes, distribution and uses of false banana in Uganda

Enset ( Ensete ventricosum ) is commonly known as the \u201cfalse banana\u201d because of its close resemblance to the domesticated banana ( Musa spp.) plant. It is Ethiopia\u2019s most important traditional staple crop in the densely populated south and south-western parts of the country; where it is grown and exploited for its starch to make various food and industrial products. In Uganda, little is known about enset regarding its ethno-botany and distribution, yet it occurs in the country. The objective of this study was to map out the distribution and document the ethno-botany and uses of enset in Uganda. A survey was carried out throughout the country to identify its natural habitats in different regions. Local people were interviewed on the uses of enset, etymology, and identification of different morphotypes. Morphological descriptors and sex of enset accessions were used in classification or identification of morphotypes. Enset was generally widely, but sparsely distributed in the different regions in Uganda; growing at elevations ranging between 988 (Moyo district) to 2,150 (Kapchorwa district) metres above sea level (masl) and in a variety of habitats. Out of the 80 districts of Uganda (as of 2009), enset was reported and observed in 30 districts. Thirteen local names of enset and their meanings were documented; but it was widely referred to as Kitembe. Different plant parts were used for medicinal purposes; while the leaves were used in local beer brewing. There were five enset morphotypes distinguished by morphological traits, such as plant height (short vs tall), mid-rib colour (light green vs pink), pseudostem background appearance (light green vs brown), leaf margin colour, male bud colour, and leaf length-breadth ratio. A detailed molecular level genetic diversity assessment is recommended for further validation of the morphotypes.Le Bananier d\u2019Abyssinie ( Ensete ventricosum ) est commun\ue9ment appel\ue9 comme \uab\ua0fausse banane\ua0\ubb \ue0 cause de sa tr\ue8s grande ressemblance au plant de banane ( Musa spp) domestiqu\ue9. C\u2019est un aliment de base traditionnel tr\ue8s important dans les r\ue9gions de grande densit\ue9 de population du Sud et Sud-Ouest d\u2019Ethiopie\ua0; o\uf9 il est cultiv\ue9 et exploit\ue9 pour son amidon utilis\ue9 pour divers produits alimentaires et industriels. En Ouganda, tr\ue8s peu d\u2019informations relatives \ue0 son ethnobotanique et \ue0 sa distribution sont disponibles sur Bananier d\u2019Abyssinie, pourtant il est pr\ue9sent dans le pays. L\u2019objective de cette \ue9tude \ue9tait de cartographier la distribution et de documenter l\u2019ethnobotanique et les usages du bananier d\u2019Abyssinie en Ouganda. Une enqu\ueate a \ue9t\ue9 conduite \ue0 travers le pays pour identifier ses habitats naturels dans diff\ue9rentes r\ue9gions. Les populations locales ont \ue9t\ue9 interview\ue9es sur les usages du bananier d\u2019Abyssinie, l\u2019\ue9tymologie, et l\u2019identification des diff\ue9rents morphotypes. Les descripteurs morphologiques et le sexe des accessions du bananier d\u2019Abyssinie ont \ue9t\ue9 utilis\ue9s dans la classification ou l\u2019identification des morphotypes. Le bananier d\u2019Abyssinie a \ue9t\ue9 largement, but sporadiquement distribu\ue9 dans les diff\ue9rentes r\ue9gions en Ouganda\ua0; les altitudes de cultures varient entre 988 (district de Moyo) \ue0 2150 m\ue8tres (district de Kapchorwa) au-dessus du niveau de la mer (masl) et dans une vari\ue9t\ue9 d\u2019habitats. Sur les 80 districts (comme en 2009), le bananier d\u2019Abyssinie a \ue9t\ue9 rapport\ue9 et observ\ue9 dans 30 districts. Les treize noms locaux du bananier d\u2019Abyssinie et leurs significations ont \ue9t\ue9 document\ue9s\ua0; mais il a \ue9t\ue9 largement r\ue9f\ue9r\ue9 au Kitembe. Les diff\ue9rentes parties du plant ont \ue9t\ue9 utilis\ue9es \ue0 des fins m\ue9dicinales, alors que les feuilles ont \ue9t\ue9 utilis\ue9es dans la pr\ue9paration de la bi\ue8re locale. Il y avait cinq morphotypes du bananier d\u2019Abyssinie distingu\ue9s par des traits morphologiques, tels que la hauteur du plant (courte vs haute), couleur de mid-nervure (vert-clair vs rose), fond d\u2019apparence de pseudo tige (vert-clair vs marron), couleur de la marge de la feuille, m\ue2le mais la couleur, et un ratio longueur/largeur de la feuille. Une \ue9valuation d\ue9taill\ue9e de la diversit\ue9 g\ue9n\ue9tique mol\ue9culaire est recommand\ue9e pour davantage validation des morphotypes

Optimisation of in vitro techniques for Cassava brown streak virus elimination from infected cassava clones

Cassava brown streak disease (CBSD), caused by Cassava brown streak virus (CBSV), is an economically important disease of cassava ( Manihot esculenta Crantz) in East Africa. The objective of this study was to optimise in vitro techniques for CBSV elimination from infected Ugandan cassava cultivars. Using semi-solid half-strength Murashige and Skoog (MS) basal medium, hormone concentration and heat treatment regimes were optimised for micropropagation of farmer's preferred cassava cultivars and CBSV elimination. Single nodes from young cassava stems were cultured for four weeks on 1/2MS medium supplemented with 6-benzyl amino purine (BAP) and 2,4-dichlorophenoxy acetic acid (2,4-D). The BAP and 2,4-D concentration (mg 1-1) combinations used were 0.0 and 0.0, 0.5 and 0.1, 1.0 and 0.2, 1.5 and 0.3, and 2.0 and 0.4, respectively. The optimum medium was used for in vitro thermotherapy using four temperature regimes, namely 30-34, 34-38, 36-40 and 38-42 \ub0C for 8 hours darkness and 16 hours light, respectively, for four weeks. The best plantlet growth in terms of height was observed on MS medium supplemented with 0.5 mg 1-1 BAP and 0.1 mg 1-1 2,4-D. Highest CBSV elimination efficiency of 40%, with 49% plantlet survival was observed at 36 \ub1C for 8 hours darkness and 40 oC for 16 hours light. These results indicate that in vitro techniques can greatly enhance CBSV elimination and, thus, provide a means of CBSD management through dissemination and conservation of popular but CBSD susceptible cultivars.La maladie de la striure brune du manioc (CBSD) caus\ue9e par le virus de la striure brune (CBSV), est une maladie \ue9conomiquement importante du manioc ( Manihot esculenta Crantz) en Afrique de l'Est. L'objectif de cette \ue9tude \ue9tait d'optimiser les techniques in vitro pour l'\ue9limination du CBSV des cultivars ougandais infect\ue9s. En utilisant le m\ue9dium basal semi-solid half strength Murashige and Skoog, la concentration d'hormone et les regimes de traitement de chaleur \ue9taient optimis\ue9s pour la micropropagation des cultivars de manioc pr\ue9f\ue9r\ue9s par les fermiers et l'\ue9limination du CBSV. Les nodes simples des jeunes tiges de manioc \ue9taient cultiv\ue9s pendant quatre semaines sur le m\ue9dium 1/2 MS suppl\ue9ment\ue9s avec 6-benzyl amino purine (BAP) et 2,4-dichlorophenoxy acetic acid. Les combinaisons de concentrations (mg 1-1) de BAP et de 2.4-D utilis\ue9es \ue9taient 0.0 et 0.0, 0.5 et 0.1, 1.0 et 0.2, 1.5 et 0.3, et 2.0 et 0.4, respectivement. Le m\ue9dium optimum \ue9tait utilis\ue9 pour la thermoth\ue9rapie utilisant quatre regimes de temp\ue9rature dont 30-34, 34-38, 36-40 et 38-42 \ub0C pendant 8 heures en obscurit\ue9 et 16 heures sous lumi\ue8re, respectivement pendant quatre semaines. La meilleure croissance en hauteur des plantules \ue9tait observ\ue9e sur le m\ue9dium MS suppl\ue9ment\ue9 avec 0.5 mg 1-1 BAP et 0.1 mg 1-1 2,4-D. L'efficience la plus \ue9lev\ue9e de 40 % en terme d'\ue9limination du CBSV, avec 49 % de la survie de plantules \ue9tait observ\ue9e \ue0 36 \ub0C pendant 8 heures sous obscurit\ue9 et 40 \ub0C pendant 16 heures sous lumi\ue8re. Les r\ue9sultats indiquent que les techniques in vitro peuvent grandement promouvoir l'\ue9limination du CBSV et offrent ainsi un moyen de gestion de CBSD \ue0 travers la dissemination et la conservation des cultivars aussi populaires que susceptibles au SBSD

Detection of cowpea aphid-borne mosaic virus (CABMV) in cowpea by reverse transcription polymerase chain reaction

The occurrence of CABMV on cowpea ( Vigna unguiculata L. Walp) in Uganda was described recently in several studies. This study developed and optimised a reverse transcription polymerase chain reaction (RT-PCR) based assay for the detection of CABMV in leaf samples, and compared it to previous RT-PCR and ELISA assays. Use of the forward primer (CABFF1, 5'- GGT AAC AAY AGT GGR CAA CC-3') and the reverse primer (CABRR1, 5'- CTG AGC ACT CMA ACC GGG-3') yielded a product of ~ 1,642 bp. Amplicon sequencing and subsequent BLASTN analysis showed that Ugandan isolates were 89.3-94.3% identical indicating they belong to the same strain of CABMV. Phylogenetic analysis also placed the Ugandan isolates in the same cluster different from other isolates but closer to those from Burkina Faso. However, the previously reported RT-PCR assay (GF/GR primer pair) did not give the expected PCR fragment (221 bp) and gave no virus hits upon amplicon sequencing and sequence analysis. The ELISA assay did not differentiate between positive and negative samples. The newly developed RT-PCR assay for detecting CABMV, described in this study, has important applications for plant quarantine, resistance breeding, host range studies as well as epidemiological studies for the control of CABMV in the country.L\u2019apparition de CABMV sur le ni\ue9b\ue9 ( Vigna unguiculata (L.)) en Ouganda a \ue9t\ue9 d\ue9crite r\ue9cemment dans plusieurs \ue9tudes. Cette \ue9tude a d\ue9velopp\ue9 et optimis\ue9 un essai bas\ue9 sur la transcription inverse- r\ue9action en cha\ueene par polym\ue9rase (RT-PCR) pour la d\ue9tection du CABMV dans les \ue9chantillons de feuilles, et la compar\ue9 aux essais pr\ue9c\ue9dents bas\ue9s sur la RT-PCR et ELISA. L\u2019usage de l\u2019amorce direct (CABFF1, 5'- GGT AAC AAY AGT GGR CAA CC-3\u2019) et d\u2019amorce r\ue9verse (CABRR1, 5'- CTG AGC ACT CMA ACC GGG-3') a donn\ue9 ~ 1,642 bp. Le s\ue9quen\ue7age d\u2019amplicon et l\u2019analyse subs\ue9quente de BLASTN ont montr\ue9 que les isolats d\u2019Ouganda \ue9taient \ue0 89,3-94,3% identiques indiquant qu\u2019ils appartiennent \ue0 la m\ueame souche de CABMV. Les analyses phylog\ue9n\ue9tiques ont aussi plac\ue9 les isolats Ougandais dans la m\ueame classe qui est diff\ue9rente des autres isolats mais proche de ceux du Burkina-Faso. N\ue9anmoins, les essais de RT-PCR (GF/GR paire d\u2019amorces) pr\ue9c\ue9dents n\u2019ont pas donn\ue9 les fragments PCR esp\ue9r\ue9s (221 bp) et n\u2019ont donn\ue9 aucune d\ue9tection de virus \ue0 partir du s\ue9quen\ue7age d\u2019amplicon et de l\u2019analyse de la s\ue9quence. L\u2019essai de l\u2019ELISA n\u2019a pas diff\ue9renci\ue9 entre les \ue9chantillons positifs et n\ue9gatifs. L\u2019essai RT-PCR nouvellement d\ue9velopp\ue9 pour d\ue9tecter le CABMV, d\ue9crit dans cette \ue9tude, a d\u2019importantes applications pour la mise en quarantaine de la plante, s\ue9lection pour la r\ue9sistance, les \ue9tudes des gammes d\u2019h\uf4tes ainsi que les \ue9tudes \ue9pid\ue9miologiques pour le contr\uf4le du CABMV dans le pays

IN VITRO PROPAGATION OF THREE COMMERCIAL PASSIONFRUIT VARIETIES IN UGANDA

Small purple ( Passiflora edulis f. edulis ) and yellow ( P. edulis f. flavicarpa ) and KPF 4 (a cross between the two varieties) passionfruit varieties are of high economic importance in Uganda. Production of passionfruit is greatly constrained by viral diseases, leading to significant yield losses. This is aggravated by lack of adequate quantities of clean planting material. In vitro propagation through nodal sections is one way that has been successful in rapidly producing planting materials of vegetatively propagated crops that are clean and true-to-type. This study was aimed at obtaining optimum in vitro growth conditions for rapid micropropagation of the commercial passionfruit varieties in Uganda. Surface sterilised nodal sections from two month old plants were used as explants. For shoot regeneration, explants were cultured on Murashige and Skoog (MS) media, supplemented with varying concentrations of 6-Benzylaminopurine (BAP), either singly or in combination with Kinetin (KIN). Rooting MS media was fortified with varying concentrations of 1-Naphthalene acetic acid (NAA), either singly or in combination with BAP. MS medium supplemented with a combination of 2 mg l-1 BAP and 0.5 mg l-1 KIN, optimally supported shoot regeneration of the three passionfruit varieties. The average number of shoots and shoot height were 3.3 and 3.1 cm, respectively. Optimal root development was observed on MS media containing 3 mg l-1 NAA, with a mean number of 5.5 leaves and a length of 2.4 cm. The rooted in vitro plantlets were successfully established in a potting mixture containing loam soil and manure in ratio of 1:1.Les vari\ue9t\ue9s de fruit de la passion petit violet ( Passiflora edulis f. edulis ), jaune ( P. edulis f. flavicarpa ) et KPF 4 (croisement r\ue9alis\ue9 entre les deux vari\ue9t\ue9s pr\ue9c\ue9dentes) sont d\u2019une importance \ue9conomique tr\ue8s \ue9lev\ue9e en Ouganda. La production du fruit de la passion est sujette \ue0 aux maladies virales, causant d\u2019\ue9normes pertes de rendement. Ceci est aggrav\ue9 par l\u2019inexistence en quantit\ue9 suffisante des semences de qualit\ue9. La propagation In vitro au moyen des sections nodales, est un proc\ue9d\ue9 qui a connu du succ\ue8s dans la production rapide des semences de bonne qualit\ue9 chez les plantes \ue0 propagation vegetative. La pr\ue9sente \ue9tude a \ue9t\ue9 r\ue9alis\ue9e afin de d\ue9terminer les conditions optimales de croissance in vitro en vue d\u2019une micropropagation rapide des vari\ue9t\ue9s commerciales de fruit de la passion en Ouganda. Des sections nodales pr\ue9lev\ue9es sur des plants de fruit de la passion ages de deux mois, ont \ue9t\ue9 st\ue9rilis\ue9es en surface et utilis\ue9es comme explants. Pour la r\ue9g\ue9n\ue9ration plantulaire, les explants ont \ue9t\ue9 cultiv\ue9s sur des milieu de culture Murashige et Skoog (MS), additionn\ue9s de diverses concentrations de 6- Benzylaminopurine (BAP), soit uniquement ou en combinaison avec de la Kinetine (KIN). Le milieu de culture MS pour la croissance racinaire a \ue9t\ue9 renforc\ue9 avec diverses concentrations de 1-Naphthalene acide ac\ue9tique (NAA), soit uniquement ou en combinaison avec BAP. Le milieu MS additionn\ue9 de 2 mg l-1 BAP et 0,5 mg l-1 KIN, a permis une r\ue9g\ue9n\ue9ration optimale des explants des trois vari\ue9t\ue9s test\ue9es. Le nombre moyen de plantule et la longueur des racines \ue9taient respectivement de 3,3 et 3,1 cm. Un d\ue9veloppement racinaire optimal a \ue9t\ue9 observe sur milieu MS contenant 3 mg l-1 NAA, avec une moyenne de 5,5 feuilles et une longueur moyenne de 2,4 cm. les plantules in vitro ont repiqu\ue9es sur pots contenant un m\ue9lange de sol argileux et de la fumure dans des proportions 1:1

HERITABILITY ANALYSIS OF PUTATIVE DROUGHT ADAPTATION TRAITS IN SWEETPOTATO

Drought stress is a constraint to sweetpotato ( Ipomoea batatas L. (Lam)) production in many parts of Sub-Saharan Africa. In this region, crop farming is predominantly rain fed; therefore, breeding for drought tolerance is appropriate for addressing low sweetpotato productivity since the crop is largely produced by resource-limited farmers. As part of developing drought tolerant genotypes in Uganda, this study aimed at determining the nature of genetic control and heritability associated with selected drought adaptation traits. Ten randomly chosen clones from each family were evaluated for three traits; tuber yield, crop vigour and canopy cover as well as five traits (leaf senescence, leaf rolling, leaf retention, SPAD readings and root vertical pulling) at 80% field capacity and under no watering conditions for three weeks in a glasshouse. Diallel analysis revealed significant effects for both GCA and SCA, indicating both additive and non-additive gene actions were present. Baker\u2019s ratio was large in most traits (>0.50), indicating predominance of additive effects. Heritability coefficients were high in most traits (>0.50), indicating that genetic gains can be achieved by conventional breeding. The predominance of additive genetic control realised in this study implies that use of small numbers of parents with suitable GCA effects is most appropriate for drought tolerance improvement in sweetpotato.La s\ue9cheresse constitue une contrainte importante \ue0 la production de la patate douce ( Ipomoea batatas L. (Lam)) dans beaucoup de parties de l\u2019Afrique sub Saharienne. Dans cette r\ue9gion, l\u2019agriculture est \ue0 predominance pluviale, ainsi, l\u2019am\ue9lioration pour la tol\ue9rance \ue0 la s\ue9cheresse est appropri\ue9e pour adresser la faible productivit\ue9 de la patate douce d\u2019autant plus que la culture est largement produite par les fermiers \ue0 resources limit\ue9es. Comme contribution au d\ue9veloppement des genotypes tolerant la s\ue9cheresse en Ouganda, cette \ue9tude a pour but de d\ue9terminer la nature de l\u2019heritabili\ue9 et le contr\uf4le g\ue9n\ue9tique associ\ue9s aux traits d\u2019adaptation \ue0 la s\ue9cheresse. En suite, dix clones al\ue9atoirement choisis dans chaque famille \ue9taient \ue9valu\ue9s au champs pendant dix huit semaines pour trois traits dont le rendement en tubercules, la vigueur de la plante et la couverture de la canop\ue9e ainsi que cinq traits (la senescence foliaire, l\u2019enroulement de la feuille, la retention foliaire, ls lectures du SPAD et l\u2019attrait de la racine verticale) \ue0 80% de la capacit\ue9 au champ et sans r\ue9gime de conditions d\u2019arrosage pendant trois semaines dans une serre). L\u2019analyse Diall\ue8le a r\ue9v\ue9l\ue9 des effets significatifs pour le GCA et SCA, indicant la pr\ue9sence des actions additives et non additives de g\ue8nes. Le rapport de Baker \ue9tait large dans laplupart des traits (>0.50), indicant la pr\ue9dominance des effets addidifs. Les coefficients d\u2019heritabilit\ue9 \ue9taient \ue9lev\ue9s dans la plupart des traits (>0.50), montrant que des gains g\ue9n\ue9tiques peuvent \ueatre acquis par l\u2019am\ue9lioration conventionnelle. La pr\ue9dominance du contr\uf4le g\ue9n\ue9tique additif r\ue9alis\ue9 dans cette \ue9tude implique que l\u2019utilisation d\u2019un petit nombre de parents avec effets GCA appropri\ue9s est la plus indiqu\ue9e pour l\u2019am\ue9lioration de la tol\ue9rance \ue0 la s\ue9cheresse dans la patate douce

Distribution of potato viruses in Uganda

Viral diseases are among the major factors affecting potato ( Solanum tuberosum L.) production in Uganda. Knowledge of the types of viruses and their distribution levels in the country is vital for targeting sound management strategies. The objective of this study was to assess the prevalence and distribution of potato viruses in different potato growing areas in Uganda. Virus diagnostic surveys were conducted across the main potato producing regions and virus detection was done using DAS-ELISA and RT-PCR techniques. The study showed that the most widely distributed and economically important potato viruses were: PVS (31-90.9%), PLRV (2.6-81.3%), PVY (7.1-54.5%) and PVX (8.3 -53.3%); while the least detected viruses were PVM (18.2%) and PVA (9%). The viruses were prevalent either singly or in mixtures. Up to 42.8% of the samples were infected with one virus, 20.9% with two viruses and 4.2% with three viruses; while no virus was detected in 31.3% of the samples. Of the double infections, the PVY+PVS combination was the most common and widely distributed (2.1-18.2%) in 12 districts; followed by PVY+PLRV (1.8-21.3%) occurring in six districts, PVM+PVS (7.9-16.7%), PLRV+PVX (2.4-14.3%) in 5 districts and PVY+PVX (2.4-4.4%) in 3 districts. Triple infections involving PVY+PLRV+PVS were recorded at prevalence levels of 2.2-18.6% in six district. Altitude, temperature, varieties and seed sources showed relationships with the variation in the prevalence of the viruses. There were high virus prevalence and disease severity levels in low altitude areas (1088-1334 m.a.s.l) of mid-western sub-region (Mbarara and Lwengo), Central (Kibaale, Mubende) and Mid Northern (Pader) sub region compared to high altitude areas (>1600 m.a.s.l). The Virus risk Area Modeling results showed the largest area (48.6%; 1,308,160 ha) at moderate risk of virus infection; while 27.3% (732,305 ha) was at high risk of virus infection. Based on the distribution level of the viruses, potato production could be intensified in areas with less virus pressure mainly, in parts of West Nile and Rwenzori regions.Les maladies virales sont l\u2019un des principaux facteurs affectant la production de pommes de terre ( Solanum tuberosum L.) en Ouganda. La connaissance des types de virus et de leurs niveaux de distribution en Ouganda est essentielle pour cibler des strat\ue9gies de gestion rationnelles. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer la pr\ue9valence et la distribution des virus de la pomme de terre dans diff\ue9rentes zones de culture de la pomme de terre en Ouganda. Des enqu\ueates de diagnostic viral ont \ue9t\ue9 men\ue9es dans les principales r\ue9gions productrices de pommes de terre et la d\ue9tection des virus a \ue9t\ue9 effectu\ue9e \ue0 l\u2019aide des techniques DAS-ELISA et RT-PCR. L\u2019\ue9tude a montr\ue9 que les virus de la pomme de terre les plus largement r\ue9pandus et les plus importants sur le plan \ue9conomique \ue9taient: PVS (31-90,9%), PLRV (2,6-81,3%), PVY (7,1-54,5%) et PVX (8,3% -53,3%); tandis que les virus les moins d\ue9tect\ue9s \ue9taient le PVM (18,2%) et le PVA (9%). Ces virus \ue9taient r\ue9pandus seuls ou en m\ue9langes. Jusqu\u2019\ue0 42,8% des \ue9chantillons \ue9taient infect\ue9s par un virus, 20,9% par deux virus et 4,2% par trois virus; alors qu\u2019aucun virus n\u2019a \ue9t\ue9 d\ue9tect\ue9 dans 31,3% des \ue9chantillons. Parmi les doubles infections, la combinaison PVY + PVS \ue9tait la plus courante et la plus r\ue9pandue (2,1 \ue0 18,2%) dans 12 districts; suivi de PVY + PLRV (1,8-21,3%) survenant dans six districts, PVM + PVS (7,9-16,7%), PLRV + PVX (2,4-14,3%) dans 5 districts et PVY + PVX (2,4-4,4%) dans 3 les quartiers. Des infections triples impliquant PVY + PLRV + PVS ont \ue9t\ue9 enregistr\ue9es \ue0 un niveau de pr\ue9valence de 2,2 \ue0 18,6% dans six districts. L\u2019altitude, la temp\ue9rature, les vari\ue9t\ue9s et les sources de semences ont montr\ue9 une relation avec la variation de la pr\ue9valence des virus. La pr\ue9valence du virus et la gravit\ue9 de la maladie virale \ue9taient \ue9lev\ue9es dans les zones de basse altitude (1088-1334 m d\u2019altitude) de la sous-r\ue9gion du centre-ouest (Mbarara et Lwengo), du centre (Kibaale, Mubende) et du centre-nord (Pader) par rapport aux zones de haute altitude (> 1600 m d\u2019altitude). Les r\ue9sultats de la mod\ue9lisation des zones \ue0 risque viral ont montr\ue9 que la plus grande zone (48,6%; 1 308 160 ha) pr\ue9sente un risque mod\ue9r\ue9 d\u2019infection virale; tandis que 27,3% (732 305 ha) \ue9taient \ue0 haut risque d\u2019infection virale. Sur la base du niveau de distribution des virus, la production de pommes de terre pourrait \ueatre intensifi\ue9e dans les zones o\uf9 la pression virale est moindre, principalement dans certaines parties des r\ue9gions du Nil occidental et de Rwenzori