Carry-over effect of Thidiazuron on banana in vitro proliferation at different culture cycles and light incubation conditions

Thidiazuron (TDZ) is an active cytokinin that was shown to induce increased shoot proliferation and habituation in black walnut, Phaseolus lunatus and evergreen azalea, which are tree species but has not been widely investigated in bananas. Unlike other cytokines commonly in use that are adeninebased, TDZ is a urea based cytokinin and therefore is  non-degradable by cytokinin-oxidase enzymes in plant tissues. This quality causes TDZ to be persistent in tissues hence transforming them from cytokinin dependence to cytokinin autonomy. This therefore makes use of TDZ cost effective but there is lack of information on this quality in banana micropropagation. A study was therefore conducted to investigate the carry over effect of varying concentrations of TDZ and 22.2 mM benzylaminopurine (BAP) as control on proliferation of five banana cultivars on a hormone free medium under various incubation conditions. The results showed that TDZ had a carry-over effect that enabled shoots to continue proliferating on a hormone free medium as the culture cycles increased and that this effect was significantly (P<0.05) higher than that of BAP. Accumulation of TDZ to high levels resulted in suppression of shoot proliferation but on exposing such tissues to a cytokinin-free medium insubsequent subcultures would result in increased shoot proliferation and elongation. The results further showed dark conditions enhanced higher proliferation rates than light conditions in some cultivars suggesting that banana in vitro proliferation is a photomorphogenically responsive processthat is enhanced under dark conditions

TDZ AND 4-CPPU in Gamborg B5 salts with MS vitamins doubles embryogenic 191 response from male flowers of EA-AAA banana.

Conventionally, auxins have been used in MS medium in combination or without purine-based cytokinins for induction of embryogenesis in EA-AAA banana (Musa spp.). Besides, low embryogenic response, it has been rare for more than two cultivars to respond similarly to a single treatment. This study investigated the efficacy of urea-type cytokinins, N-phenyl-N’-1,2,3-thidiazol-5-ylurea (TDZ) and N-(2-chloro-4-pyridyl)-N'-phenylurea (4-CPPU); and salt formulations, Chu (N6), Eriksson, Gamborg B5, MS, Nitsch, NLN, SH and White for embryogenic callus induction in different EA-AAA banana cultivars. Immature male flowers of cultivars Mpologoma, Mbwazirume, Nakabululu, Nakinyika and Nfuuka were cultured on callus induction medium, supplemented with different TDZ and 4-CPPU combinations. Most of the cultivars had embryogenic response to the medium with 10μM TDZ+10μM CPPU. Cultivar Nakabululu recorded 22.2% embryogenic response, followed by Mwazirume (5.7%), Nakinyika (5.3%) and Mpologoma (4.6%). Cultivar Nfuuka had 9.1% embryogenic response on 15μM TDZ+15μM CPPU. When cultivars Mpologoma and Nakinyika were cultured on the same medium containing 10μM TDZ+10μM CPPU, but the MS salts substituted with the other salt formulations, their cultures recorded 11.4 and 8.3% embryogenic response, respectively to Gamborg B5 salts; which was almost twice their response to MS medium. The results suggested that TDZ and 4-CPPU, particularly in Gamborg B5 salt formulation, could increase percentage of embryogenic callus induced from male flowers of EA-AAA banana cultivars, and would improve plant regeneration and consequently help in the process of genetic improvement of EA-AAA banana.Key Words: Cytokinins, embryogenic response, Musa spp., Thidiazuro

Generation of cell suspensions of East African highland bananas through scalps

The improvement of East African highland bananas (EAHBs) using conventional breeding methods is difficult due to their biology and therefore focus on improving them has shifted to exploring methodsfor establishment of embryogenic cell suspensions, which can then be targeted, for genetic transformation. Shoots of four cultivars namely ‘Musakala’, ‘Kibuzi’, ‘Mbwazirume’ and ‘Lwadungu’ were transferred to a multiplication media modified by adding a combination of N6-benzylaminopurine (BAP) and thidiazuron (TDZ) at concentrations of 24.8/0.45, 16.2/1.14, 14.4/3.50, 12.4/4.55, 10/5.68 mM forscalp generation. These media are referred to as M1, M2, M3, M4 and M5, respectively. Two other treatments designated as M6 and M7 with concentrations of 10 mM TDZ and 100 mM BAP, respectivelywere included for comparison purposes. The scalps developed were excised and inoculated into liquid induction medium supplemented with either BAP or Zeatin to generate cell suspensions. Scalpformation was achieved earlier and at much lower concentrations of combined BAP and TDZ than when singly applied. Combinations of 12.4/4.55 and 10/5.68 M BAP/TDZ produced the best scalps. Thestructure of the cell suspension and the rate of cell growth were found to be dependent on the cultivar regardless of the hormone treatment in the induction medium. Cultivars ‘Musakala’, ‘Kibuzi’ and ‘Mbwazime’ produced cell culture of clustered and aggregated cells and high cell numbers, which are a prerequisite for embryo cells development

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

Male Fertility in Uganda Banana Germplasm

Identification of fertility levels in banana germplasm collection at Kabanyolo, Uganda, was conducted by dehiscing the anthers using a glass rod. The study involved 151 accessions. The quantity of pollen grains per anther was ranked 0-5; where 0 had no grains and 5 had abundant pollen grains. A correlation between pollen output and inflorescence characters revealed a positive relationship (r = 0.69, P ≤ 0.01) to inflorescence diagnostic characters. A quantitative determination of pollen output per anther and percentage pollen viability based on starch test using the Heamocytometer method revealed that the amount of starch filled grains did not proportionally vary with the total pollen output. Pollen output varied from cultivar to cultivar. Most East African highland banana cultivars were found to have more pollen than the recently introduced banana cultivars. A few highland banana cultivars were non-polleniferous. The results indicate the relative potential of using various cultivars in hybridization and, anther and pollen culture programmes.Keywords: Bananas, Heamocytometer, fertility, polle

Testing for a suitable culture medium for micropropagation of East african higland bananas

No Abstract

Variability in the root system of East African banana genotypes

The banana (Musa spp.) root system is important for plant anchorage and the uptake of nutrients and water and thus, strongly influences plant growth and subsequent yields. Previous research studies on the Musa spp. root system have predominantly focused on high value export dessert bananas (AAA group) and plantains (AAB group). The study reported in this paper compared root system development of East African highland bananas (AAA-EA group) with other Musa groups. Two separate studies were conducted. One of the studies focused on variability in root system development of 25 Musa genotypes, including 10 East African highland bananas, while the other experiment assessed variability in root distribution for ‘Kibuzi' (AAA-EA, cooking banana), ‘Gonja' (AAB, plantain) and ‘Sukali Ndiizi' (AAB, dessert banana). Plants in the first study were completely excavated at 20 weeks after planting (WAP), while a sub-set of 5 East African highland bananas was also assessed at flower emergence. A 90° section of the root system was assessed for pre-flowering plants in the second trial. Significant positive correlations were found between shoot and root traits for the plants assessed at 20 WAP and at flower emergence. In addition, there was no significant genotypic effect on the shoot root ratio indicating that all genotypes had a similar partitioning of dry matter between the shoot and the root system. In contrast, at 20 WAP significant genotypic effects were observed on individual shoot and root traits. Soil depth and genotype significantly (

Biochemical and secondary metabolites changes under moisture and temperature stress in cassava (Manihot esculenta Crantz)

Cassava’s (Manihot esculenta Crantz) importance as a food security crop in Sub Saharan Africa is enhanced by its special traits such as tolerance to drought and high yields under drought stress. However, full understanding of tolerance mechanisms under hydrothermal stress in cassava is a key in developing highly tolerant varieties with increased yield. In our study, the effects of low soil moisture and increased temperature on cassava physiology were investigated. Twenty (20) cassava varieties were evaluated in a Randomized Complete Block Design in western Uganda. Hydrothermal stress was described as a period of no rainfall for a period of eight weeks leading to low soil moisture (contents between 28 to 35%) and average daily temperatures of ≥35°C. The average daily relative humidity during this period was considerably low (≤40%) further complementing already enhanced stress conditions. As such, the contents of important biochemicals and secondary metabolites in the plants were altered in a bid to counteract the effects of stress. Significant differences occurred in accumulation of main biochemicals such as soluble proteins (P<0.05), free reducing sugars (P<0.05) and bound reducing sugars (P<0.05) while reductions in the total starch yield by 70 to 100% of the original composition before stress were observed in all the test varieties. Changes in pigment properties were also observed with a decrease in the total carotenoid content (~65%) and chlorophyll a (Chla) (~40%) but no significant changes were observed for chlorophyll b (Chlb). Secondary metabolites such as phenolics and tannins too depicted varied but non-significant changes and they existed in low quantities. There were also significant changes in the phenotype (foliar portion of the plant) with at least two mechanisms of tolerance identified. The study showed the importance of carbohydrate and nitrogen cycle related metabolites in mediating tolerance in cassava by affecting their phenotypic expression in the plant.Keywords: Hydrothermal stress, bio-chemicals, pigments, secondary metabolites, cassava.African Journal of Biotechnology, Vol 13(31) 3173-318

Population studies of fungal plant pathogens: Perspectives for control with specific reference to grey leafspot

Plant diseases hinder food production globally. Of the known crop plant pathogens, fungi are perhaps the most widely adapted organisms. For disease control, host resistance has been the main method used through major gene deployment. Equally important, has been the use of fungicides. Over the last two decades these two control strategies have been fraught with rapid resistance erosion commonly referred to as the “boom and burst cycle,”. This raises urgent concerns with regard to development of effective alternative strategies such as use of fungicides. The use of fungicides is an effective strategy but they are potential sources of pollution into the environment, pose serious health risks to humans and are uneconomical for low-resource farmers. In this article the potential of how improved disease management strategies embodied in integrated disease management (IDM) can be developed based on a clear understanding of the pathosystem is discussed. We demonstrate that population and molecular genetics can be used to define pathosystems, estimate the evolutionary responsiveness of pathogens and from the data, design appropriate durable control methods. Various population and molecular genetic methodologies are described and how they can be incorporated into standard pathogen characterisation studies. Using grey leaf spot of maize (Cercospora zeae-maydis) as a case study, we show how these techniques can be used to generate information on genetic variability, providing for logical development of a durable IDM programme. Key words: Cercospora zeae-maydis, disease management, genetic tools, molecular markers RÉSUMÉ Les maladies de plante entravent globalement la production de nourriture. Des pathogènes de plante connus, les champignons sont peut être les plus rependus organismes adaptés. Pour le contrôle de maladie, la résistance hôte a été la méthode principale utilisée à travers le déploiement de gène majeur. Egalement important, a été l'usage des fongicides. Pour plus de deux décennies ces deux stratégies de contrôle ont été angoissées avec une rapide érosion de résistance communément connu à nous comme “boom and burst cycle” (cycle de boom et d'explosion). Ceci soulève les inquiétudes urgentes avec respect au développement des stratégies alternatives effectives comme l'usage des fongicides. L'usage des fongicides est une stratégie effective mais ces fongicides sont des sources potentielles de pollution dans l'environnement, pose des risques sérieux de santé aux humains et ne sont pas économiques pour les fermiers de faibles ressources. Dans cet article le potentiel de comment les stratégies améliorées de gestion des maladies incarnées dans une gestion intégrée des maladies (IDM) peut être développé basé sur une compréhension claire du pathosystème est discutée. Nous démontrons que la population et les génétiques moléculaires peuvent être utilisés pour définir les pathosystèmes, estimer les non réponses évolutionnaires des pathogènes et à partir des données, concevoir des méthodes de contrôle durables. Diverses populations et méthodologies génétiques moléculaires sont décrites et comment elles peuvent être incorporées dans les études de caractérisation de pathogène standard. Utilisant la tache grise de feuille de maïs (Cercospora zeae-maydis) comme cas d'étude, nous montrons comment ces techniques peuvent être utilisées pour générer l'information sur la variabilité génétique, pourvoyant le développement logique d'un programme d'IDM durable. Mots clés: Cercospora zeae-maydis, gestion de maladie, outils génétiques, indicateur moléculaire African Crop Science Journal Vol.12(4) 2004: 327-34