RP-Department of Plant and Microbial Sciences
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Browsing RP-Department of Plant and Microbial Sciences by Author "Alakonya, Amos E."
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Item Bioactivity determination of methanol and water extracts for roots and leaves of Kenyan Psidium guajava L landraces against pathogenic bacteria(springerplus, 2013) Alakonya, Amos E.; Mercy, Liharaka Kidaha; Aggrey, Benard NyendePsidium guajava L) is native to South America and exists as both wild and cultivated. Guava has been used as a source of food and raw materials for pharmaceuticals. The aim of this study was to determine bioactivity of methanol and water extracts from root and leaves of Kenyan guava landraces against selected pathogenic bacteria. Study samples were collected from Western and South Coast of Kenya. One hundred grams of leaf and root ground powders were used for sequential extraction using methanol and water. Extracts were evaporated and 0.2gms dissolved using the extraction solvent and tested against gram positive (Staphylococcus aureus, Bacillus subtilis) and negative bacteria (Escherichia coli). Data on inhibition zone was taken in mm and analyzed at 95% confidence interval. Extracts from Western region had significant inhibition compared to Coastal region. The two regions have different climatic conditions that result in these plants having different compounds even though they are the same species. Roots had higher inhibition compared to the leaves as they contain high levels of tannins compared to leaves. Water as an extracting solvent had higher inhibition than methanol as it is more polar and it absorbs more bioactive compounds. S. aureus was most inhibited followed by E. coli and B. subtilis respectively. There was no significant difference between the gram positive and negative bacteria. Remarkably, some methanol and water root extracts had significant inhibition against bacteria when compared to some commercial antibiotics used. Results of this study indicate that Kenyan guava roots from Western Kenya extracted with methanol and water have a potential to be used as a source of active compounds in treatment of gram positive and gram negative bacteria pathogens.Item Efficacy of selected medicinal plants from Eastern Kenya against Aspergillus flavus(2014) Kiswii, M.T.; Monda, E. O.; Bii, Christine; Alakonya, Amos E.Aflatoxins are a major problem in Eastern Province of Kenya and Aspergillus flavus has been associated with frequent outbreaks of aflatoxicoses in this region. This study evaluated the efficacy of 15 selected medicinal plants from Eastern Kenya against A. flavus. Different concentrations of 1000mg/ml, 750mg/ml and 400mg/ml using Agar Well Diffusion Method were used. Plants found to have inhibition zones of more than 10mm at 400mg/ml had their bark further assayed for antifungal activity. Both the leaf and bark extracts that were found to be effective were assayed for minimum inhibition concentrations (MIC) and minimum fungicidal concentrations (MFC) using Sabouraund Dextrose broth (SDB) micro-dilution method. The methanolic leaf and bark extracts of the fifteen plants assayed displayed concentration depended antifungal activities that was comparable to that of the reference drug Miconazole at 10mg/ml. Leaf extracts showed better antifungal activity than the bark extracts. For instance, Boscia coriacea (mean 17.40mm) had the highest zone of inhibition followed by Zanthoxylem chalybeum (mean 17.20mm). For the bark extracts, Croton megalocarpus (mean 15.0mm) recorded significantly high antifungal activity while Tithonia diversfolia (mean 13.0mm) had the lowest at 400mg/ml. Senna siamea had the lowest MIC and MFC of 6.25mg/ml and 12.5mg/ml respectively. The preliminary phytochemical analysis of the 15 effective medicinal plants revealed the presence of bioactive compounds that included tannins, saponins, flavonoids, terpenoids, cardiac glycosides and alkaloids. The results obtained from the study could be used as a viable management strategy against A. flavus and aflatoxins in the region so as to ensure low mycotoxin exposure as well as low environmental pollutionItem Fumonisin b1 and aflatoxin b1 levels in kenyan maize(Journal of Plant Pathology, 2009) Alakonya, Amos E.; Monda, E. O.; Ajanga, S.Maize ear rot is an important disease of maize in Kenya. In this study fumonisin Bx (FBj) and aflatoxin Bx (AFBj) analysis were conducted on symptomless and rotten maize harvested at different harvest time points after physiological maturity (HTPAPM). Fusarium verti- cillioides dominated at all HTPAPM. Other fungi re- ported include Aspergillus flavus, Aspergillus parasiticus and Sternocarpella may dis. In 2001, FBX levels in symp- tomless maize ranged between 22 to 1348 pg/kg. Mean FBj levels at 4, 8, and 12 weeks HTPAPM for Malava were 56, 80 and 317 jig/kg respectively. In Tongaren during 2001 mean FBl levels of 41, 179 and 590 pg/kg were recorded at 4, 8, 12 week HTPAPM respectively. The FBj levels in rotten maize ranged from 39 to >5000 pg/kg and increased with HTPAPM. The highest AFB1 level was 17 pg/kg in rotten maize. The results suggest that delayed harvesting could increase FBX contamina- tion in maize. Maize ear rot, Fusarium verticillioides, As- pergillus flavus , mycotoxins, food safety.Item Lack of GFP Trafficking from Transgenic Nicotiana benthamiana to Parasitizing Cuscuta pentagona(IDOSI Publications, 2010) Alakonya, Amos E.; Runo, Steven; Dan, K; Monda, E. O.; Machuka, Jesse; Sinha, N.This work reports lack of GFP transport from transgenic N. bethamiana under the control of constitutive promoter CAMV 35S to Cuscuta pentagona. The data on N. bethamiana and C. pentagona host-parasite system suggests that macromolecular trafficking from host to parasite is host–parasite specific and such results should not be generalized outside the system studied. This data further suggests that molecular trafficking from host to parasite through either symplastic or apoplastic mechanisms is not fully understood. This is so for as especially the gating mechanisms involved. Macromolecular trafficking between host and parasite holds potential application in parasitic plant management and in basic research. It is therefore important to investigate why such contradictions exist in even very closely related host parasite systems like the genera Nicotiana and Cuscuta.Item Management of Fusarium verticillioides Root Infection Court in Maize Using Organic Soil Amendments(World Applied Sciences Journal, 2008) Alakonya, Amos E.; Monda, E. O.; Ajanga, S.Abstract: In this study the efficacy of various soil organic amendments were evaluated for their potential to manage Fusarium verticillioides root infections in maize. The soil organic amendments used were neem cake, sunflower cake, cotton cake, goat manure and farmyard manure. In a field experiment F. verticillioides was inoculated to seed holes with different soil organic amendments at planting. Soil and root samples were collected for mycological analysis at 10, 30 and 60 days after silking. Upon maturity maize was harvested at 4 and 8 weeks after physiological maturity where assorted data was collected. Rotten and symptomless maize samples were collected and subjected to mycological and mycotoxin analysis. Significantly high recovery rates of F. erticillioides from control soil and roots than in amended soil was evident. At 60 days after silking the percent recovery of F. verticillioides was reduced to even zero in some treatments indicating that organic soil amendments have a mechanism of suppressing the survival of F. verticilliodes in the soil and hence limit its root infection ability. Mycological analysis on symptomless kernels revealed high recovery of F. verticilliodes from in control plots than amended treatments indicating the ability of the amendment to manage root infections of F. verticilliodes. Mycotoxin analysis revealed widespread FB1 contamination across treatments and in both asymptomatic and rotten maize. Average FB1 in symptomless maize was 333.98 μg kg and 357.4 μg kg at 4th 1 1 and 8th weeks after physiological maturity respectively. All rotten maize samples had over 5000 μg kg 1 of FB .1Aflatoxins were only present in three samples at 4th week after physiological maturity. The results show that soil organic amendments could limit root infection by F. erticillioides however, it cannot if singly used as a management strategy against the pathogen guarantee 100% eradication of the pathogen and associated mycotoixins. This therefore calls for an integrated approach that could involve use of resistant hybrids, soil solarization, early land preparation, insect control, fungicide treated seed and good post harvest handling practices. Mycotoxin ignorant maize consumers in Africa especially need to be educated on the risks they face if they consume rotten maize given the very high levels of FB1 revealed in this study and elsewhere. Key words: Infection court Fumonisins Aflatoxins Organic soil amendments Ear rot fungi ELISA Zea mays KenyaItem No More Free Lunch: Using RNA Interference in the Host to Reduce Growth of a Parasitic Plant(American Society of Plant Biologists, 2012) Alakonya, Amos E.; Kumar, R.; Koenig, D.It is generally correct to think of plants as the hearty autotrophs, gamely harnessing photons to make food and existing perennially (or annually) at the bottom of the food chain. However, thousands of plant species have lost the ability to feed themselves and have become adapted, instead, to live as parasites of other plants. Not surprisingly, these parasitic plants, especially witchweed root parasites such as Striga and Orobanche, have become major agricultural problems, causing substantial agricultural losses in regions where resources such as water are limited. Parasitic plants grow penetrating structures called haustoria, which connect to the vasculature of the host, allowing them to take water and nutrients from the host plant. Removing a parasite is a not so simple matter of finding a treatment that will kill the parasite, but not the host. When both host and parasite are plants, the matter becomes increasingly complicated (reviewed in Rispail et al., 2007). Agronomic practices such as crop rotation and selective herbicides have proved to be of limited usefulness. Moreover, genetic resistance for resistance to parasitic plants has been difficult to find and has only proven successful in a few instances, although transgenic and marker-assisted selection strategies may provide more success. These complications show that novel strategies will be required to control these damaging parasites. Macromolecules can be transferred from host to parasite; for example, RNA interference (RNAi) has been proposed, and explored with limited success, as one potential mechanism to control plant parasites (reviewed in Yoder et al., 2009). Alakonya et al. (pages 3153–3166) use the broad host-range parasitic plant dodder (Cuscuta pentagona) and the host plant tobacco (Nicotiana tabacum) to test an RNAi strategy. For the RNAi target, their examination of gene expression found that KNOTTED-like homeobox (KNOX) transcription factors are upregulated during early haustorial development, and they focus specifically on the KNOX factor SHOOT MERISTEMLESS-like (STM). KNOX factors affect cell differentiation in the shoot apical meristem and induce cytokinin biosynthesis, which is required for haustorium formation. The authors next express an RNAi construct targeting dodder STM in the tobacco host plants. To avoid affecting the host, they express the STM RNAi construct under the control of an Arabidopsis thaliana vasculature-specific promoter, targeting the RNAi to tissues that interact with the parasite. The authors detect STM-specific small RNAs in both the transgenic tobacco host and in the dodder grown on that host. They also find that, when growing on STM-RNAi tobacco, dodder shows strong downregulation of STM, poor establishment, limited growth (see figure), early onset of flowering, and reduced seed set. Therefore, with STM as a starting point, the authors show that novel strategies such as RNAi have strong potential for the control of parasitic plants.Item An optimized protocol for high frequency regeneration of selected groundnut (Arachis hypogaea L) varieties from East Africa using cotyledons(International Journal of Agriculture and Crop Sciences., 2013) Alakonya, Amos E.An efficient protocol for regenerating high yielding groundnut varieties; ICGV-CG2 and CG2 through direct organogenesis has been optimized using 6-benzylaminopurine and 2,4- dichlorophenoxyacetic acid. Murashige and Skoog medium with B5 vitamins was supplemented with individual treatments of BAP and 2,4-D and with their combinations to induce shoot bud formation. Preliminary results showed no shoot formation on media with the individual plant growth regulators. The highest and lowest regeneration requencies in CG2 were 93.33% and 36.67% respectively on medium supplemented with 1 mg/L 2,4-D and 4.5 mg/L BAP. In ICGV-CG2 the highest frequency was 90% on media with 1.5 mg/L 2, 4-D and 4.5mg/L BAP with a low of 46.67%. Three (3) to ten (10) shoots were recorded per explant, with a maximum of ten shoots recovered from the best performing plant growth regulator regimes. Shoots elongated on MS with reduced BAP levels (0.75-4.5mg/L), rooted on media with α-naphthalene acetic acid and later acclimatized in the glasshouse on peat moss. Hardening and growth of plants to maturity was achieved in the glasshouse on a sand-soil mixture (1:1 w/w) in pots. In vitro induction of flowers in one of the explants could have been as a result of somaclonal variation. This work has developed an optimized protocol that sets up a platform for improvement of these varieties that are adapted to East Africa with novel genes through genetic transformationItem Use of organic soil amendments in management of fusarium moniliforme(African Crop Science Society, 2013) Alakonya, Amos E.; Monda, E. O.; Owino, P. O.; Ajanga, S.Efficacy of soil amendments in management of root infection by Fusarium moniliforme was evaluated in the greenhouse at Kenyatta University. The amendments used were neem cake, sunflower cake, cotton cake, goat manure, farmyard manure (Fym), and a combination of Fym with neem cake, sunflower cake, cotton cake, or goat manure. F. moniliforme used was isolated from kernels in western Kenya, a maize ear rot disease prevalent region. Seeds of a susceptible maize variety H622 seeds were used during the study. Non-amended soil acted as the control. Plants were harvested at 30,60 and 90 days after planting. At every interval, plant length, shoot dry weight, root dry weight were assessed. Pathogen recovery from the soil, roots, crown and node was also evaluated at the intervals. The results revealed that different soil organic amendments had significant effects on the pathogenecity of F. moniliforme and plant performance. Goat manure had significant suppressive effects on root infection when used singly, but the effects were less than those obtained from a mixture of goat/Farm yard manure. Efficacy of various amendments were rated as follows starting from the most to the least effective; goat, goat/Fym, neem/fym, cotton, Fym, cott/Fym, sun/fym, neem and sunflower respectively. In general organic amendments reduced the survival and infection of maize plants by F. moniliforme compared to controls. The population of F. moniliforme reduced gradually with time after planting. Results from this study suggest that the use of organic amendments might be a viable option in the management F. moniliforme in areas where the pathogen is prevalent. Key words: Fusarium moniliforme, ear rot, maize, soil organic amendments.