Relationship between Tomato Yellow Leaf Curl Viruses and the Whitefly Vector

Abstract · Tomato yellow leaf curl is prevalent in tomato growing districts of Uganda. The disease is known to be spread by a whitefly (Bemisia tabaci) in a persistent manner. Some of its symptoms are leaf curl, marginal leaf yellowing, malformation of fruits, stunting and dieback (in case of primary infection at early seedling stage), so the disease is economically important. Therefore, this study delved into the relationship between the disease and the vector in selected agro-ecosystems in the Country. The influence of weather and seasonality on the incidence of the disease and the vector was also investigated through a series of field experiments across a period of two years. New methods for trapping the vector were developed and applied to estimate its populations on individual plants and in the overall field environment. The findings were that whereas incidence of the disease is low at seedling stage, the whitefly population is highest at this stage. It was also found that the vector population is favoured by drought, so rainy conditions reduced it tremendously

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

Timing and distribution of attack by the banana weevil (Coleoptera: curculionidae) in East African highland banana (Musa spp.)

Timing and distribution of attack on East African highland banana (Musa AAA- EA) by the banana weevil, Cosmopolites sordidus (Germar), (Coleoptera: Curculion- idae) was studied in a field trial at a farm 25 km NE of Kampala, Uganda. Weevils were released at three densities (5, 20 and 40 females per mat) in 324 m' banana plots (cv Atwalira) that had been established 18 months earlier and maintained relatively free of weevils. Two weeks after release, entire mats were removed and examined for weevil eggs and first instar larvae. At a density of 20 weevils per mat, oviposition occurred on 25% of plants less than 6 six months old (suckers) with an average of three eggs (range 0-16) per infested plant. At the same time, 85% of flowered plants were at- tacked with mean oviposition of 15 eggs (range 0-41) per plant. An inverse relation- ship existed between weevil population density and eggs/female/plant. Five females per mat produced an average of 7.2 eggs per flowered plant, whereas 20 females pro- duced 15 eggs per flowered plant and 40 females produced 12.5 eggs. This suggests the existence of density-dependent factors in weevil oviposition. Over 90% of the oviposi- tion occurred in the base of the pseudostem, with the remaining eggs found in the corm and roots near the soil surface. However, in stands displaying high mat, (a con- dition in which part of the corm appears above the soil surface) more eggs were found on the corm than pseudostem

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

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

Portable PCR field-based detection of sweetpotato viruses

Sweetpotato ( Ipomoea batatas Lam.) production is greatly constrained by viral infections, especially Sweet potato feathery mottle virus and Sweet potato chlorotic stunt virus that synergistically cause a severe sweetpotato virus disease. The impact of viruses is aggravated by the vegetative nature of the crop and inaccessibility to dependable diagnostic tools in rural areas where sweetpotato production is done. This makes it hard for seed inspectors to perform quality checks prior to use of vines for planting. The objective of this study was to develop a procedure that allows for detection of sweetpotato viruses on-site. This involved modification of the Lodhi et al. (1994) nucleic acid extraction procedure, by omitting some of the laboratory specific steps and varying the incubation time in liquid nitrogen, instead of the freezer. Incubation in liquid nitrogen for only 1.5 hours yielded as high quality RNA compared to that of the original protocol, when incubation was done at 4\ub0C overnight in a freezer. Reverse transcriptase (RT) was run using a portable miniPCR thermocycler; and the resulting cDNA was amplified using this miniPCR machine instead of using a laboratory stationed conventional PCR thermocycler. The cDNA was efficiently amplified and amplicons were similar to those obtained with the original extraction protocol and subsequent amplification by the conventional RT-PCR. Our protocol reduced extraction time from about 16 hours for the original protocol, to about 2 hours and 45 minutes. If this tool is utilised by the crop protection departments, we believe it will contribute greatly towards sustainable sweetpotato production through making timely recommendations.La production de la patate douce ( Ipomoea batatas Lam.) est fortement limit\ue9e par les infections virales, en particulier le virus de la marbrure plumeuse de la patate douce et le virus du stunt chlorotique de la patate douce qui provoquent en synergie une maladie virale grave de la patate douce. L\u2019impact des virus est aggrav\ue9 par la nature v\ue9g\ue9tative de la culture et l\u2019inaccessibilit\ue9 des outils fiables pour le diagnostic dans les zones rurales o\uf9 la production de patate douce est r\ue9alis\ue9e. Cela rend difficile les inspecteurs des semences d\u2019effectuer des contr\uf4les de qualit\ue9 avant l\u2019utilisation des vignes par les agriculteurs. L\u2019objectif de cette \ue9tude \ue9tait de d\ue9velopper une proc\ue9dure permettant la d\ue9tection des virus de la patate douce sur place. Cela impliquait une modification de Lodhi et al. (1994) proc\ue9dure d\u2019extraction d\u2019acide nucl\ue9ique, en omettant certaines des \ue9tapes sp\ue9cifiques du laboratoire et en faisant la variation de temps d\u2019incubation dans l\u2019azote liquide, au lieu du cong\ue9lateur. L\u2019incubation dans l\u2019azote liquide pendant seulement 1,5 heure a donn\ue9 un ARN de haute qualit\ue9 comme le protocole d\u2019origine, lorsque l\u2019incubation a \ue9t\ue9 effectu\ue9e \ue0 4 \ub0 C pendant une nuit dans un cong\ue9lateur. La transcriptase inverse (RT) a \ue9t\ue9 faite en utilisant un thermocycleur mini PCR portable et l\u2019ADNc, et r\ue9sultant a \ue9t\ue9 amplifi\ue9 en utilisant cette machine mini PCR au lieu d\u2019utiliser un thermocycleur PCR conventionnel stationn\ue9 en laboratoire. L\u2019ADNc a \ue9t\ue9 efficacement amplifi\ue9 et les amplicons \ue9taient similaires \ue0 ceux obtenus avec le protocole d\u2019extraction original et l\u2019amplification ult\ue9rieure par la RT-PCR conventionnelle. Notre protocole a r\ue9duit le temps d\u2019extraction d\u2019environ 16 heures pour le protocole d\u2019origine, \ue0 environ 2 heures et 45 minutes. Si cet outil est utilis\ue9 par le d\ue9partement de la protection des cultures, nous pensons qu\u2019il contribuera grandement \ue0 la production durable de patate douce en faisant des recommandations en temps opportun

Detection and Elimination of Sweetpotato Viruses

In sub-Saharan Africa, sweetpotato ( Impomoea batatas L.) production is greatly constrained by sweetpotato virus disease (SPVD) complex. This study was conducted to assess the incidence of viruses in healthy-looking sweetpotato in Uganda and to optimise modern technologies for virus diagnosis. A collection of healthy-looking sweetpotato vines from central Uganda were serologically assayed for sweetpotato viruses and the positive samples were confirmed by RT-PCR. A multiplex RT-PCR assay was optimised for simultaneous detection of Sweet potato chlorotic stunt virus (SPCSV), Sweet potato feathery mottle virus (SPFMV) and Sweet potato mild mottle virus (SPMMV). The use of in vitro thermotherapy was also investigated as a means of eliminating sweetpotato viruses. Four viruses namely SPCSV, SPFMV, SPMMV and SPCFV were detected mostly as single infections in the healthy looking plants. SPCSV (70. 6%) recorded highest incidence followed by co-infection of SPFMV and SPCSV (8.3%). Based on shoot survival and effectiveness of virus elimination, the best results were obtained by exposing plantlets to daily temperature regime of 32 \ub0C for 8 hr of darkness and 36 \ub0C for 16 hr of light for four weeks. Meristem-tip culture combined with thermotherapy allowed elimination of SPFMV and SPMMV in 77% of plants that were previously infected with the respective viruses. However, elimination of SPCSV was unsuccessful.En Afrique sub saharienne, la production de la patate douce ( Impomoea batatas L.) est grandement affect\ue9e par un complexe de maladies de virus (SPVD). Cette \ue9tude \ue9tait conduite pour \ue9valuer l'incidence maladie des virus sur des boutures apparemment saines de la patate douce en Ouganda et optimiser les technologies pour diagnostic de virus. Des boutures apparemment saines de patate douce collect\ue9es au centre de l'Ouganda \ue9taient s\ue9rologiquement test\ue9es et les \ue9chantillons infect\ue9s \ue9taient confirm\ue9s par RT-PCR. Un essai multiplexe RT-PCR \ue9tait optimis\ue9 pour la detection simultan\ue9e du virus du rabougrissement chlorotique de la patate douce (SPCSV), le virus de la marbrure duveteuse de la patate (SPSMV) et le virus de marbrure mod\ue9r\ue9e de la patate douce (SPMMV). L'usage de la thermoth\ue9rapie in vitro \ue9tait aussi test\ue9 comme moyen d'\ue9limination des virus de la patate. Quatre virus dont SPCSV, SPFMV, SPMMV et SPCFV \ue9taient detect\ue9s surtout comme seules infections des plantes apparemment saines. Le SPCSV (70. 6%) avait pr\ue9sent\ue9 une incidence \ue9lev\ue9e, suivi de SPFMV et SPCSV dont le niveau d'infection \ue9tait le m\ueame (8.3%). Bas\ue9 sur la survie des pousses et l'efficacit\ue9 de l'\ue9limination de virus, les meilleurs r\ue9sultats \ue9taient obtenus en exposant les plantules \ue0 un regime de temp\ue9rature de 32 \ub0C pendant 8 heures sous obscurit\ue9 et 36 \ub0C pendant 16 heures sous lumi\ue8re durant quatre semaines. La culture du bout du m\ue9rist\ue8me combin\ue9e \ue0 la thermoth\ue9rapie a perimis l'\ue9limination de SPFMV et SPMMV dans 77 % des plants qui \ue9taient au d\ue9part infect\ue9s avec des virus respectifs. Par ailleurs, l'\ue9limination de SPCSV avait \ue9chou\ue9

Performance of selected grain sorghum genotypes for improved food security and livelihoods

Sorghum is a useful cereal crop cultivated by numerous resource poor farmers in semi arid regions. The crop is indigenous thus well adapted to various environments in Kenya. Sorghum performs better than other cereal staples particularly maize especially during extended dry periods. Experiments to determine the performance of different sorghum genotypes were conducted. Results showed that grain yield varied significantly (Pd”0.01) among the genotypes evaluated. The best four ranked performers in decreasing order were Kari-mtama 1, IESV 930 SH, IS 27329 and Seredo