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Articles by J.W. Kimenju
Total Records ( 11 ) for J.W. Kimenju
  A.K. Chirchir , J.W. Kimenju , F.M. Olubayo and G.K. Mutua
  A study was conducted to determine the factors influencing plant-parasitic nematode occurrence, abundance and distribution in the sugarcane fields. Four sugarcane growing zones; Nzoia, Mumias, West Kenya and Busia of Kenya were selected from which 81 fields randomly selected and sampled. Soil samples were taken from sugarcane rhizospheres and nematodes extracted from 200 cm3 soil using the modified Baermann funnel technique. Nematodes were then fixed and mounted on slides and identified to genera level using identification keys. Nematodes of the genera Pratylenchus, Scutellonema and Meloidogyne were predominant in the sugarcane belt of western Kenya with mean densities of 61, 54 and 39, respectively. Nzoia, which falls in a marginal sugarcane zone harboured the highest proportion of these plant parasitic nematodes (55%), while West Kenya zone had the least proportion (4%). Soil texture influenced nematodes with more than 50% occurring in sandy soils compared to other soil types. Build-up of plant parasitic nematodes occurred with subsequent ratoon crops up to the second ratoon before declining in the third ratoon. Anthropogenic effects were significant with 70% higher numbers of plant parasitic nematodes in the out-grower farms compared to the factory-managed farms. This study has revealed the influence of soil texture, crop cycle and anthropogenic factors on abundance and distribution of plant parasitic nematodes in western Kenya sugarcane zones. It has also set the justification of further work to determine the economic importance of the nematodes.
  A.K. Chirchir , J.W. Kimenju , F.M. Olubayo and G.K. Mutua
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  J.O. Nyasani , J.W. Kimenju , F.M. Olubayo , S.I. Shibairo and G.K. Mutua
  This study was aimed at determining the occurrence of entomopathogenic nematodes (EPNs) in different agroecosystems and their potential as biocontrol agents in the management of DBM. Soil samples were taken from a planted forest, pasture, a coffee field and a vegetable garden. EPNs were isolated from the soil using Galleria mellonella as the bait insect. Laboratory bioassays were conducted to determine the lethal time fifty (LT50), which is time till 50% lethality, of the EPN isolates to DBM larvae using the leaf disc bioassay method. Five isolates of EPNs namely Heterorhabditis indica, Steinernema karii, Steinernema wesieri, Steinernema sp. and Heterorhabditis sp. were used. The frequency of occurrence of EPNs was lowest, 27%, in the soil from vegetable garden, followed by forest soil, 33%. EPNs were present in 50 and 77% of the soil samples from pasture and coffee ecosystems, respectively. The LT50 of S. karii, H. indica and S. wesieri was 38.10, 20.27 and 23.80 h, respectively. Heterorhabditis indica, S. karii, S. wesieri, Steinernema sp. and Heterorhabditis sp. caused 96.0, 93.3, 92.0, 88.0 and 86.7% mortality in the DBM larvae within 72 h, respectively. This study has demonstrated that the frequency of occurrence of EPNs is different in various agroecosystems. The study has also showed that EPNs have a great potential that may be exploited along with other suitable strategies in integrated management of DBM.
  J.W. Kimenju , A.M. Kagundu , J.H. Nderitu , F. Mambala , G.K. Mutua and G.M. Kariuki
  Green manure plants were evaluated to determine their suitability as rotation crops with common bean to suppress root-knot (Meloidogyne spp.) nematodes. They were also evaluated as soil amendments in nematode control. The plants were Calliandra calothyrsus, Canavalia ensiformis, Chenopodium quinoa, Crotalaria juncea, Desmodium uncinatum, Gliricidia sepium, Leucaena leucocephala, Mucuna pruriens, Tephrosia purpurea, Tithonia diversifolia, Vicia villosa, Sesbania sesban and Tagetes minuta. In the glasshouse, pots were filled with steam-sterilized soil and sown with green manure plants. The rotation experiment entailed growing green manure plants for three months before uprooting them and planting beans in the same pots. The potting medium was infested with 6000 eggs/juveniles of Meloidogyne javanica. The field experiments were carried out in microplots infested with a mixture of M. javanica and M. incognita. Damage to bean roots due to root-knot nematodes was based on galling indices while nematode reproductive potential was based on egg mass index. Tithonia diversifolia, D. uncinatum, T. minuta, L. leucocephala and C. juncea were among the most effective in root-knot nematode suppression when used in rotation with beans. Their galling indices ranged between 1.0 and 1.5 under field conditions and were thus considered resistant. Vicia vilosa, T. purpurea and S. sesban were susceptible with galling indices ranging between 6.2 and 7.7. The resistant plants reduced the reproductive potential of Meloidogyne spp. by up to 80% while the susceptible plants caused an increase of up to 600%. Therefore, T. diversifolia, D. uncinartum, T. minuta, L. leucocephala and C. juncea can be recommended for use in fields infested with root-knot nematodes.
  A.N. Mweke , J.W. Kimenju , A.A. Seif , E.W. Mutitu and G.K. Mutua
  The response of different crops to a mixed population of root-knot nematodes, Meloidogyne javanica and M. incognita and their potential as suppressants in sequential cropping systems was evaluated in greenhouse and field experiments. Crops rated as resistant were five maize cultivars, four sorghum cultivars, two millet varieties, guwar and two pigeonpea cultivars which had galling indices ranging between 1.4-3.6. cowpea cv. K80 was rated as moderately resistant with a galling index of 4 while greengram and cowpea cv. KKI were rated as susceptible with galling indices ranging from 5.6 to 7.4. Four crops namely sweetcorn, babycorn, maize cv. Pioneer (Ph3253) and guwar were selected after the greenhouse tests for field trials, based on their poor host status to root-knot nematodes as well as relative acceptability to vegetable growers. These crops were then incorporated into a rotation program with okra. Initial and final J2 numbers in the field were determined before planting and at the end of the season, respectively. Okra was then sown in the plots previously grown with the selected nematode suppressive crops and the nematode numbers determined mid and end of the season. A 44 and 21% decline in nematode numbers was recorded in plots under guwar or sweetcorn and babycorn, respectively. In contrast, a 441% increase in nematode numbers was recorded in plots under continuous crop of okra. The galling index on a crop of okra that followed sweetcorn was 3.3 compared to 8.6 in the control which was continuously under okra, resulting in an increase in yield within a range of 60-92%. This underscores the potential of rotating highly susceptible crops with poor hosts in the management of root-knot nematodes.
  J.K. Langat , J.W. Kimenju , G.K. Mutua , W.M. Muiru and W. Otieno
  This study was carried out with the aim of evaluating the effect of ecologically sound approaches for nematode management on non-target organisms, free-living nematodes. The materials tested were sugarcane bagasse, molasses, tea and flower composts, neem (Achook), a biological agent (Paecilomyces lilacinus) and fenamiphos (Nemacur). The treatments were administered before planting carnation var. White Natila in flower beds that were naturally infested with nematodes. Application of bagasse, molasses, tea and flower composts resulted in increased abundance of free-living nematodes compared to the control where nothing was applied. Bacterial feeders, fungal feeders, and predators comprised 73, 14 and 13%, respectively of the free-living nematodes recovered. Members of the genus Rhabditis were the most abundant (10%) among the bacteriovores while Mononchus (10%) and Aphelenchoides (14%) dominated among the predators and fungivorous trophic groups, respectively. The highest numbers of free-living nematodes were recorded at 90 Days after Planting (DAP) in plots treated with bagasse and molasses but the numbers declined at 180 DAP. A steady increase in numbers of free-living nematodes was observed in plots treated with tea and flower composts up to 180 DAP. Significant reductions in abundance of free-living nematodes were recorded in plots treated with fenamiphos and neem. This study has established that application of organic substrates serve as a stimulus to processes leading to build-up of free-living nematodes. The organic substrates can strongly be recommended for use in sustainable carnation production systems.
  P.M. Wachira , J.W. Kimenju , S. Okoth , R.K. Mibey and J. Mung`atu
  This study was undertaken with the objective of determining the occurrence of nematode destroying fungi in soil under different land use systems, with the ultimate goal of harnessing their potential in the control of plant parasitic nematodes. Soil samples were collected from an indigenous forest, maize/bean, napier grass, shrub and vegetable fields, which represented the main land use types in Taita Taveta district of Kenya. The fungal isolates obtained were grouped into seven genera the species identified were Arthrobotrys oligospora, A. dactyloides, Monacrosporium cionopagum, A. superba, Harposporium anguillulae, Harposporium sp., Dactyllela lobata, Acrostalagums obovatus, Haptoglosa heterospora and Nematoctonous georgenious. Occurrence of nematode destroying fungi was significantly (P: 3.81x10-7) different among the land use systems in the study area. Out of the isolates that were positively identified, 33.7, 27.9, 20.9, 11.6 and 5.8% were from fields under vegetable, maize/bean, napier grass, shrub and forest, respectively. The diversity of nematode destroying fungi was highest in the maize/bean fields and lowest forest soil. Fungal isolates from vegetable gardens were most diverse but the least even while the forest land use was most even but least diverse. The total richness of nematode destroying fungi was 9, in vegetable and maize/bean fields while was 7, 6 and 3 in napier, shrub and forest habitats, respectively. This study has established that nematode destroying fungi are widely distributed and that land use has a significant effect on their diversity.
  P.M. Wachira , J.W. Kimenju , S.A. Okoth and R.K. Mibey
  A screenhouse experiment was conducted to evaluate the effect of cow manure, chicken manure and their combinations on nematode destroying fungi, nematode community and growth of tomato (Solanum lycopersicum L.). The amendments were applied at the rate of 5% w/w in all the treatments. Isolation of nematode destroying fungi was done using the soil sprinkle technique. Nematodes were extracted from soil using the modified Baermann technique. Tomato growth was estimated through plant height and dry weight. Application of the organic amendments resulted in significant differences (p≤0.05) in occurrence of nematode destroying fungi amongst the treatments. The nematode destroying fungi occurred at frequencies of 50, 29.4, 17.6 and 2.9% in soil amended with chicken manure, cow/chicken combination, cow manures and the control, respectively. Eight species of nematode destroying fungi were identified in this study. The fungus Arthrobotrys oligospora (Fresenius) was most dominant fungus in all the treatments including control pots with an isolation frequency of 38.2%. Addition of organic amendments into the soil also resulted in an increase of bacterial and fungal feeding nematodes and reduction of plant parasitic nematodes. Specifically there was a 225, 96 and 62% increase in bacterial feeding nematodes and 391, 96 and 74% increase in fungal feeding nematodes in soil amended with chicken manure alone, combination of chicken and cow manure alone in that order. Numbers of plant-parasitic nematodes were 92% lower in soil treated with chicken manure compared to the control. Plant height and leaf widths were highest in plants treated with combination of cow and chicken manures. The plants mean dry weight were 6.6, 5.6, 2.0 and 1.5 in combination of chicken and cow manure, chicken manure alone, cow manure alone and control, respectively. This study has therefore, revealed that organic amendments stimulate the occurrence of nematode destroying fungi in the soil and also reduce plant parasitic nematodes. In addition, the combination of cow and chicken manure stimulates plant growth.
  J.W. Kimenju , G.O.M. Odero , E.W. Mutitu , P.M. Wachira , R.D. Narla and W.M. Muiru
  This study aimed at evaluating the suitability of selected substrates for mushroom production. Ten different substrates namely water hyacinth (Eichhornia crassipes), maize cobs (Zea mays), coconut fibre (Cocos nucifera), finger millet straw (Seteria microcheata), banana fibre (Musa sp.), sawdust (Eucalyptus sp.), rice straw (Oryza sativa) bean straw (Phaseolus vulgaris) and wheat straw (Tritichum aestivum) were tested for their suitability in mushroom production. Plastic bags were filled with 250 g of substrate and arranged in a randomized complete block design. The substrates had a significant (p≤0.05) effect on days to pinning, number of caps and biological efficiency. Compared to the control, which pinned at 28 days, maize cobs, sawdust and coconut fiber had short pinning durations of 19, 22 and 23 days, respectively. With the exception of sawdust, water hyacinth and maize cobs, the rest of the organic substrates significantly increased the marketable caps of the oyster mushroom. The straws, namely, bean, rice, finger millet and wheat had the highest biological efficiency in decreasing order of 106, 92, 85 and 77%, respectively. Stipe length was longest in oyster mushroom grown on bean straw, followed by finger millet straw, maize cobs, banana fiber and shortest in sawdust. Mushroom yield was, 80, 78, 76, 73 and 68%, higher in bean straw, rice straw, millet straw, wheat straw and banana fibre treatment compared to the control. Mushroom yields on sawdust were 60% lower than the control. In descending order of suitability bean, rice, finger millet and wheat straws can be recommended for oyster mushroom production.
  W.M. Muiru , B. Koopmann , A.V. Tiedemann , E.W. Mutitu and J.W. Kimenju
  Eighty nine Exserohilum turcicum isolates comprising 56 Kenyan, 26 German and 7 Austrian isolates were isolated from diseased maize plants and cultured on complete liquid medium to generate mycelium for DNA extraction. DNA extraction was done following the CTAB method, DNA purified using spermidin and fingerprinting conducted using Amplified fragment length polymorphism (AFLP) procedure. NTSYSpc, pop gene and Arlequin programs were used to analyze the data and to generate the dendograms. The number of amplified bands and polymorphism varied with the different primer combinations with primer combinations E-ACA/T-CCA, E-ACA/T-CAC, E-ACA/T-CGA, E-ACA/T-CTA revealing a high (79%) level of polymorphism. Cluster analysis of the 607 polymorphic bands from these primer combinations using UPGMA algorithms generated dendograms with 7 main AFLP groups with isolates from different localities grouping together with only two outliers. Pair wise similarity matrix derived with SIMQUAL program showed a wide variation in the AFLP fingerprint of the E. turcicum isolates. Nei’s genetic distance matrix showed that the three populations of E. turcicum isolates differed genotypically with the Kenyan isolates being more genetically related to Austrian isolates (genetic identity of 0.9998) whereas the isolates from Germany and Austria were more diverse (genetic identity of 0.9978). This study showed that AFLP marker is useful in the study of genetic variation of E. turcicum and the pathogen has a high level of genetic diversity.
  A.G. Wagura , J.W. Kimenju and B.M. Gichimu
  Raw and processed products of Ocimum gratissimum reportedly contain some antibacterial effects. In this study, raw plant extracts and essential oils derived from leaves of Ocimum gratissimum were screened for their antibacterial properties on Ralstonia solanacearum, the causal agent of bacterial wilt in Irish potato at varying concentrations. The raw extracts were obtained through sequential cold extraction using methanol solvent while the essential oils were extracted through steam distillation. The test products were used at concentrations of 0.4, 0.2, 0.1, 0.05 and 0.025 mg mL-1. Antibacterial tests were done using paper disc diffusion inhibition method and antibacterial activity was determined by measuring the size of inhibition zones. The results showed that the five different concentrations of essential oils and plant extracts exhibited highly significant (p<0.0001) differences on their effects against growth of R. solanacearum. The study confirmed the antibacterial effects of O. gratissimum and further demonstrated that the active compound (s) against Ralstonia solanacearum is (are) concentrated in the essential oils.
 
 
 
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