RP-Department of Plant and Microbial Sciences
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Item Pea Aphid: Interaction of Insecticides and Alfalfa Varieties(Entomological Society of America, 1978-02) Mueke, J. M.; Manglitz, G. R.; Kerh, W. R.Carbofuran, methoxychlor, Mobile MCA-600 (benzo [b]thien-4-yl methylcarbamate), leptophos, methidathion, and dialifor were evaluated for control of Acyrthosiphon pisum (Harris) on the alfalfa varieties `Cody', `Dawson',` Team', and `Vernal' in the greenhouse. Dawson and Team are resistant to pea aphids; Cody and Vernal are susceptible. Use of leptophos significantly increased pea aphid numbers on the resistant variety Team but only slight increases resulted from its use on resistant Dawson, with slight decreases in pea aphid numbers following its use on susceptible Vernal. The other insecticides, with the exception of methoxychlor, effectively reduced pea aphid numbers. There were indications that carbofuran, Mobil MCA 600, leptophos, and dialifor increased growth rate of some of the alfalfa varieties, possibly because of aphid control. However, the height of Team was reduced by carbofuran, methoxychlor, and methidathion.In an outdoor cage, leptophos, as the only treatment, also significantly increased pea aphid numbers on Cody, Team, and Vernal but not on Dawson. In a field study with carbofuran, leptophos, and methidathion, the leptophos treatment increased pea aphid numbers (but not to the point of significance) on Dawson and Vernal but not on Team. It was not determined whether the increase in pea aphid numbers was due to change in physiology of the aphid or its host or both.Item The induction of a light requirement in bidens pilosa seeds by leaf canopy shade(Wiley, 1980-01) Fenner, M.The aim of these experiments was to determine whether exposure to leaf-canopy shade induces a light requirement for germination in Bidens pilosa seeds. Seeds of this species were pretreated by placing them in the shade of a natural canopy for 12 days and then setting half of them to germinate in full light and the other half in darkness. Canopy-treated seeds acquired a marked light requirement. The pretreatment was more effective if the seeds were imbibed during it. Fresh and old seeds gave similar results. In a second experiment the effect of time of exposure to canopy shade on the induction of a light requirement was investigated. It was found that only 1 h exposure to leaf-transmitted light is required to induce an almost complete light requirement in this species. The ecological implications of the results are discussed.Item The inhibition of germination of bidens pilosa seeds by leaf canopy shade in some natural vegetation types(Wiley, 1980-01) Fenner, M.The inhibition of germination by leaf canopies was investigated in Bidens pilosa, a widespread tropical colonizing weed species. Seeds of this species were sown in the shade of four natural vegetation types: early colonizing stage of an old field succession, a later stage of the same sere, short grass, and long grass. There were four control treatments: full sunlight on open soil, banana-leaf shade, ‘neutral’ shade under white paper, and darkness. Since the temperature regimes under the canopies differed, the effect of temperature on the germination of the seeds was investigated. The results show that the leaf canopies of the vegetation types investigated are markedly effective in inhibiting germination of this species in the field. Inhibition by unfavourable temperatures could have been only a contributory factor. It is suggested that seed sensitivity to leaf canopy shade may be of importance in effecting changes in species composition in early successional stages, and in excluding open-habitat species from closed vegetation generally.Item Control of the potato tuber moth (Phthorimaea operculella) (zell) in storage using dust formulated insecticides.(Ministry of Agriculture, 1980-01) Ojero, M. F. O.Tubers of potato variety Roslin Gucha were dusted with the followign insecticides:- Pirimiphosmethyl (1 percent, permethrin (1 percent) cypermethrin (0.5 percent), Fenvalarate (1 percent) and etrimfos. The adult moths were left exposed for 21 days after which the paper bags were closed and clipped for another 30 days. This was done in order to allow already laid eggs to develop. Then the tubers were examined for the tubermoth infestation. The untreated tubers were 90 percent infested which justifiedinsecticides treatments for tuber protection against (Phthorimaea operculella) (Zell). At all treatment rates, all the insecticides achieved some control except pirimiphosmethyl. All the insecticides were very effective in controlling (P operculella) infestaion. Fenvarate and etrimfos were more effective in suppressing the population of (P. operculella) in storage than permethrin, cypermethrin and pirimiphosmethyl. Although both rates to 100 and 75 gms of product per bag of potatoes were more effective than 50 gms, it is better to use 75 gm. These treatments produced good results and would be recommended for use in storage for large quantitiesItem Germination tests on thirty-two East African weed species(Wiley, 1980-06) Fenner, M.The seeds of thirty-two species of common East African weeds were set to germinate in the light and in the dark. Eighteen species with more than 40% germination in the light were also germinated in leaf shade and in neutural shade of equal intensity. Germination of fifteen of these was inhibited by darkness, and of sixteen by leaf shade, with complete inhibition in six species. A high degree of dormancy was found in fourteen species. Only one species in this group responded to alternate wetting and drying of the seeds. In eight species dormancy was less in older seeds. The ecological implications of the results are briefly discussed, and comparisons made with temperate weeds.Item Aspects of the ecology of acacia-commiphora woodland near Kibwezi, Kenya(1982-07) Fenner, M.Item Factors that influence yield in close-spaced coffee, 1: Light, dry matter production and plant water status.(Kenya Coffee (Kenia). Oct 1984. v. 49(580) p. 203-211., 1984-10) Gathaara, M. P. H.; Kiara, J. M.Photosynthetically active radiation (PAR) flux, dry matter production and partitioning and leaf water potential were compared in five tree densities with and without irrigation using the coffee cultivar SL28. The effect of PAR flux through the tree canopy on fruit, foliage and wood dry weight yield is discussed. It is concluded that the downward flux of PAR through the coffee canopy more than any other factor was the major determinant of fruit productionItem Factors that influence yield in close-spaced coffee. 2. Yield components(1985) Gathaara, M. P. H.; Kiara, J. M.Yield components (number of nodes, fruits per node, and fruits per primary branch) were compared in five densities with and without irrigation; using / Coffea arabica / var. SL-28. Measurements were taken at 3 levels of foliage. The fruits and fruit per node per primary branch fell in the lower part of the tree. Irrigation decreased production of knots, fruits per node, and fruits per primary branch in the middle and upper part of the plant. The fruits and fruit per node per primary branch had a negative linear correlation with tree density. The effect of irrigation and tree density in determining yield components is discussed. It is concluded that irrigation and short distances increase vegetative growth by reducing the passage of light through the foliage.Item Factors that influence yield in close-spaced coffee.(1985-07) Gathaara, M. P. H.; Kiara, J. M.Yield components (total and bearing nodes, fruits per node and fruits per primary) were compared in five tree densities with and whithout irrigation using Coffea arabica L cultivar SL 28. Measurements were taken at three canopy levels. Fruits per node and fruits per primary decreased down the tree canopy. Irrigation decreased bearing nodes, fruits per node and fruits per primary in the middle and bottom canopies. Fruits per node and fruits per primary had negative linear correlation with tree density. The effect of irrigation and tree density on the determination of yield components is discussed. It is concluded that irrigation and close-spacing enhanced vegetative growth which reduced light transmission through the tree canopy. This in turn resulted in poor yield parametersItem Effects of some seed advancement treatments on the germination of Coffea arabica L. [coffee hybrid] seeds [in Kenya](1986) Gathaara, M. P. H.Wighed seeds of four varieties of Coffea arabica L. were subjected to some seed advancement treatments. The treatments resulted in earlier germination but did not increase the final germination percentage. It is concluded that the treatment elicited physiological activity which resulted in rapid seed germination but did not significantly influence seed viabilityItem Effects of some seed advancement treatments on the germination of Coffea arabica L. seeds(1986) Gathaara, M. P. H.Weighed seeds of four varieties of Coffea arabica L. namely: SL28, SL34, K7 and Ruiru 11, a hybrid, were subjected to some seed advancement treatments. The treatments were allowing the seeds to imbibe known quantities of various solutions for 48 hours before drying them back to their initial weight. They were then plated out on filter papers in petri dishes. Germination counts were recorded every 24 hours. Seed advancement treatments resulted in earlier germination but did not increase the final germination percent. Acetone resulted in the fastest germination time but inhibited subsequent radicle development. It is concluded that the treatments elicited physiological activity which resulted in rapid seed germination but did not significantly influence seed viabilityItem Arabica coffee production in Kenya: an overview.(1986) Gathaara, M. P. H.; Masaba, D. M.; Owuor, J. B. O.The cultural practices, crop protection and breeding programmes in Arabica coffee in Kenya are reviewed. Examples of major insect pests are leaf miners (Leucoptera spp.), antestia bugs (Antestiopsis spp.) and scales. Major plant diseases include coffee berry disease (CBD; Colletotrichum coffeanum), coffee leaf rust (Hemileia vastatrix) and bacterial blight of coffee (Pseudomonas syringae). In the 1960s, severe losses from CBD led to the launching of an intensive breeding programme that has resulted in a new cultivar Ruiru 11 which is disease resistant, high yielding, compact in growth and produces good quality coffee. Arabica coffee in Kenya is grown on soils of volcanic origin (Kikuyu red loam soils) which have a field capacity of 1200 mm of water, and irrigation is applied when a soil moisture deficit of 150 mm is recorded. Replenishing 50-75 of this deficit is sufficientItem Plant regeneration via somatic embryogenesis in mature embryo-derived callus culture of Sinocalamus latiflora (Munro) McClure(Science Direct, 1987) Yeh, Meei-Ling; Chang, Wei-ChinSomatic embryogenesis and subsequent formation of plantlets was achieved from callus cultures derived from mature zygotic embryos of Sinocalamus latiflora (Munro) McClure (Bamboo). Embryogenic callus was initiated on Murashige and Skoog's medium (MS) supplemented with 6 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D), 3 mg/l kinetin, 250 mg/l polyvinylpyrrolidon and 5% sucrose. Prolonged culture of the embryogenic callus on the same medium resulted in embryoid formation. The embryoids developed further to yield whole plantlets when transferred to a medium containing lower concentrations of 2,4-D (3 mg/l) and kinetin (2 mg/l).Item Effects of irrigation rates and frequency on the growth and yield of arabic coffee(1988) Gathaara, M. P. H.; Kiara, J. M.A trial was set up to find out the optimum irrigation rate and interval and their effects on tree growth and yield of Arabica coffee. The irrigation rates were 38, 76 and 100 mm of water applied at 14, 21 and 28 days intervals. Results indicate that there were no significant yield differences between the rates and between the intervals. Irrigation however increased Grade "A" coffee by 43 per cent. The best rate x interval combination was 76 mm at 28 day interval which is the current practice. This was 113 kg per ha. more than 38 mm at 21 day interval. It is concluded that there was very little yield advantage occurring from the higher irrigation rates. The practical implications of these results are discussedItem Nutrient-phytoplankton relationships in a tropical meromictic soda lake(Kluwer Academic Publishers, 1988) Njuguna, S. G.Seasonal variation through one year in total nitrogen (TN), total phosphorus (TP), phytoplankton biomass, phytoplankton species composition and other environmental factors were examined in Lake Sonachi, a tropical meromictic soda lake. Mean concentrations of TN and TP were 11 000 µg N l-1 and 100 µg P l-1, respectively. Maximum concentrations of TN and TP occurred in the monimolimnion. Phytoplankton biomass ranged from 350 to 1260 mg m-3. Synechococcus bacillaris, a small coccoid cyanophyte, dominated the phytoplankton. The mean chlorophyll a concentration of 37 mg • m-3 was a modest value when compared with those of other tropical soda lakes. High TN:TP ratios indicated phosphorus limitation in the lake.Item Tree performance at close-spacing as influenced by pruning cycle and site(1988) Gathaara, M. P. H.Data on 10 years of productions / Coffea arabica / variety Caturra (dwarf type) and SL28 (high type) grown at 1400, 1600 or 1800 meters, at densities of 2,222, 3,322, 5,000 and 7,463 trees / ha, are presented pruning cycles 3, 4, 5 or 6 years. Both the highest and lowest sites, SL 28 gave the highest yields, while at intermediate sites was little difference between the productions. In mid-altitude sites, the optimal density for both cultivars was 5,000 trees / ha and 7,463 Caturra trees / ha and optimal pruning cycles were 5 and 6 years, respectively.Item Susceptibility of eight potato cultivars to Myzuz pericae Silver in the Green House.(Cambridge University Press, 1989-04) Nderitu, J. H.; Mueke, J. M.Eight potato cultivars namely Anett, Desiree, Feldeslohn, Kerr's Pink, Kenya Baraka, Roslin Eburu, Roslin Gucha and Roslin Tana were tested in the greenhouse to compare their susceptibility to Myzus persicae Sulzer. Differences in the susceptibility of the potato cultivars to aphids were reflected in the number of the apterae aphids that developed on them. Anett, Kerr's Pink and Feldeslohn supported the highest, and Roslin Tana the lowest population of M. persicae. Roslin Tana was found to be resistant. The bottom leaves of most potato cultivars maintained the highest aphid population while the upper leaves maintained the lowest. There were no significant correlations between leaf area and yield of potatoes with the number of apterae aphids on the eight potato cultivars.Item The conversion of 2-furaldehyde into some potentially useful bifunctional derivatives(Elsevier B.V., 1990) Musau, Richard. M.; Munavu, Raphael. M.2-Fluraldehyde was converted into 2-(5-R-2-furyl)-1, 3-dioxanes; 5-R-2-cyanofurans where R = H, Br, I or NO2; bis(5-bromo-2-furyl-1,2-R diimine where R = ethyl or butyl; and 5-hydroxymethyl-2-furaldehyde. Furfuryl alcohol, obtained from 2-furaldehyde by the Cannizaro reaction, and 5-hydroxymethyl-2-furaldehyde were reacted with hydrogen sulphide to give 2,2′-difurfuryl thioether in 5% yield and thiobis (5-methyl-2-furaldehyde) in 6% yield, respectively. Furfuryl alcohol reacted with 5-hydroxymethyl-2-furaldehyde to yield 5-formyl-2,2′-difurfuryl ether in 6% yield. The dioxanes were found to decompose when stored at room temperature for more than six months, while the other compounds were relatively stable when stored for the same period of time.Item Density and fertilizer requirements of the compact and disease resistant arabica coffee.(1990) Gathaara, M. P. H.; Kiara, J. M.Sixteen NPK fertilizer combinations and 6 coffee planting densities were tried in Kenya between 1981 and 1988 using the compact and disease resistant Catimor. Yield differences due to fertilizer treatments were not significant. However, yields of over 2 t/ha were obtained from NP or NPK combinations. Yield increased linearly with the planting density but peaked at 5128 trees/ha. The results are discussed. It is concluded that while the fertilizer requirements for the compact cultivar are not different from the traditional tall types the optimal density is about 5128 trees/ha. From authors' summary.Item Effects of ergostim biostimulant on the growth, yield and quality of Arabica coffee(1991) Gathaara, M. P. H.; Gitau, K. M.The effect of Ergostim (folic acid plus L-cysteine) A bioestimulante on growth, yield and quality Arabica coffee, was studied in a field trial in Kenya. Ergostim was sprayed at rates of 0, 250, 500, 750 and 1000 ml per hectare. The first application was made before flowering while the second was applied every 6 weeks later. The treatments significantly increased the growth of the expansion, the production of clean coffee beans AA class and improved the quality of the drink. It is concluded that the best treatment in terms of overall production of clean coffee was 500 milliliters per hectare.