Browsing by Author "Guthrie, E.J."
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Item Control of Cassava Mosaic Disease in Kenya(1982) Bock, K.R.; Guthrie, E.J.Mosaic disease of cassava is one of the most important factors limiting production in East Africa. The disease can be controlled by the use of healthy planting material. Plots of carefully selected apparently healthy cassava of several cultivars of differing genetic constitution were established and successfully kept free of disease by inspection and rouging. The rate of spread of mosaic disease into mosaic-free plots over a five-year period was consistently very low (less than 2% and most frequently less than 1 %l irrespective of cultivar type or size of plot (0.02-1.00 ha, which clearly indicates that mosaic disease can be effectively controlled in Kenya by the use of mosaic free propagation material. Comparative yield data indicated that yields of local cassavas are at least equal to those of improved resistant cultivars and suggest that agronomic evaluation of Kenya cultivars would be of great value.Item Measurement of Yield Losses Caused by Maize Streak Disease(1978) Guthrie, E.J.; Kenya Agriculture Research institute P.O Box 30148 Nairobi Kenya.In trials at Muguga, Kenya in 1975-6 the effect of maize streak virus on the yield on maize cv. H512 was studied. Under natural infection 19 out of 360 plants were infected and the mean grain yield was reduced by 33.3% from 156.3 to 104.3 g. When infected artificially at the 1st leaf stage grain yield was reduced by 61% from 158.5 to 61.3 g. A significant relationship was found between the stage of the plant at infection and the yield loss. Yield losses ranged from 55.3% at the 2nd leaf stage to 24.9% at the 10th leaf stage (75.7 and 127.3 g, resp. compared with 169.4 g/plant for the controls). ADDITIONAL ABSTRACT:Yield reduction of maize infected with maize streak virus was measured under field conditions at Muguga, Kenya. Losses were 25-60%. There was a strong correlation between time of infection and yield loss.Item A Note on Copper Deficiency In The Njoro Area, Kenya(1965) Pinkerton, A.; Barrett, M.W.; Guthrie, E.J.Severe yellowing and die-back of young wheat in the Njoro area in 1963 was shown to be due to copper deficiency aggravated by the application of super phosphate fertilizers.Item Notes on East African Plant Virus Diseases(1974) Guthrie, E.J.; East African Agricultural and Forestry Research OrganizationA virus collected from lettuce near Muguga, Kenya, was identified on the basis of morphology and serology as lettuce mosaic virus (LMV). The virus is seed-borne and was presumably introduced into East Africa by this means. Tests on pyrethrum, sunflower and chrysanthemum indicated that these important crop species are not susceptible to LMV.Item Occurrence of Tomato Black Ring Virus in Potato Cultivar Anett in Kenya(1978) Kaiser, W.J.; Bock, K.R.; Guthrie, E.J.; Meredith, G.; Kenya Agricultural Research Institute, Nairobi, KenyaA virus isolated from diseased potatoes cv. Anett imported into Kenya from W. Germany in the 1960s was identified on the basis of host range, particle morphology, physical properties and serology as TBRV. The Anett isolate was serologically related to the beet ringspot virus group of TBRV. It did not react with antiserum to the type (tomato) str. of TBRV or to antisera to tobacco ringspot, tomato ringspot or raspberry ringspot viruses. The host range of the Anett isolate was extensive and the virus was seedborne in several inoculated food crops and weed hosts. The virus was not transmitted by aphids or the nematode Longidorus laevicapitatus which occurs in soils of the potato-growing regions of Kenya. This is the 1st published report of TBRV on the African Continent. The importance of strict observance of quarantine in importations of potatoes is thus underlined.Item Plant Viruses with Circular Single-Stranded DNA(1977) Harrison, B.D.; Barker, H.; Bock, K.R.; Guthrie, E.J.; Meredith, G.; Atkinson, M.; Scottish Horticultural Research Institute, Invergowrie, Dundee, UK; Ministry of Overseas Development Crop Virology Project, East African Agriculture and Forestry Research Organisation, PO Box 30148, Nairobi, Kenya; MRC Virology Unit, Institute of Virology, Church St, Glasgow, UKSMALL quasi-isometric particles, mostly occurring in pairs, have been found in, and purified from extracts of plants infected by maize streak 1, beet curly top, tomato golden mosaic", euphorbia mosaic", bean golden (yellow) mosaic3 -5, cassava latent6 and cassava brown streak viruses Individual particles are 15-20 nm in diameter-unusually small for a virus-and in electron micrographs many of the individual particles in the pairs have a five-sided outline in which the contiguous sides seem longer than the others.Item Purification and Some Properties of Tephrosia Symptomless Virus(1981) Bock, K.R.; Guthrie, E.J.; Figueiredo, G.; Woods, R.D.; Overseas Development Administration/Kenya Agricultural Research Institute, Crop Virology Research Project, P.O. Box 30148, Nairobi, Kenya; Rothamsted Experimental Station, Harpenden, Herts, AL5 2JQTephrosia symptomless virus (TSV), isolated from Tephrosia villosa, is widely distributed in coastal districts of Kenya. The virus was readily transmitted by inoculation of sap, but not by Aphis craccivora or Apion sp. (Curculionidae) or through soil. Host range was very restricted and it infected only 10 of 70 species tested in one of nine plant families; susceptible species were confined to five genera within the Papilionaceae. The virus was cultured, propagated and assayed in soybean. TSV remained infective after 10 min at 85°C, 3 wk at 20°C and 26 wk at -12°C; crude infective sap of Glycine max retained infectivity when diluted 10-6 but not 10-7. Virus was purified from systemically infected soybean by clarifying sap extracted in 0.06 M phosphate buffer containing 0.001 M EDTA and 0.1% thioglycollic acid (pH 7.5) with equal volumes of 1:1 n-butanol/chloroform followed by two cycles of differential and one of sucrose density gradient centrifugation. Purified preparations contained c. 33 nm isometric particles. TSV contained RNA and one protein of molecular weight 1.53. 106 and c. 42 000, respectively. Analytical centrifugation indicated a single component with a sedimentation coefficient (s.20, w) of 127 S; in Cs2SO4 and CsCl isopycnic gradients a single virus band formed; buoyant density in CsCl was 1.361. TSV was not related serologically to any of 44 viruses in nine plant virus groups but it resembled the tombusviruses and other ungrouped viruses such as carnation mottle in some of its properties.Item Purification of maize streak virus and its relationship to viruses associated with streak diseases of sugar cane and Panicum maximum(1974) Bock, K.R.; Guthrie, E.J.Maize streak virus (MSV) was purified by homogenising infected leaf tissue in 0·01 MpH 3'9 phosphate buffer and clarifying the extract with n-butanol (7 ml/loo ml extract). Purified preparations contained particles 20 nm in diameter, some occurring singly, but most occurring in pairs, forming structures of 30 x 20 nm. The sedimentation coefficients of single and paired particles were S4 and 76 S respectively.Item Transmission of African Cassava Mosaic by Mechanical Inoculation(1978) Bock, K.R.; Guthrie, E.J.; Agriculture and Forestry Research Organization, Nairobi, KenyaThe disease agent (presumably a virus) was transmitted from cassava to cassava by sap inoculation. Transmissions were made in phosphate or borate buffers or in deionized water.Item Transmission of African Cassava Mosaic by Mechanical Inoculation(1978) Bock, K.R.; Guthrie, E.J.; Agriculture and Forestry Research Organization, Nairobi, KenyaThe casual agent of the cassava mosaic disease was transmitted from cassava to cassava by using a standard method of inoculation of plant viruses, the manual inoculation of infective sap. Transmission were made in phosphate or borate bufers, kor in deinozed water. Mosaic disease of cassava (Manihot esculenta) is the most important factor limiting yield of the crop in Africa (8). The causal agent, which is presumed to be a virus (9), is known to be transmitted by grafting and by the whitefly, Bemisia tabaci (2,9). Storey and Nichols (9) were unable to substantiate early reports of experimental transmission by injection of infective sap (4) or by needle scratch (3). They also failed to transmit the disease by rubbing young leaflets with infective sap. The Plant Disease Reporter, Volume 62 transmission of African Go Great interest has recently been shown in African cassava mosaic disease (CMD), and efforts have been renewed to isolate and characterize the pathogen (1,6). Several Institutes have attempted electron microscopy of ultrathin sections of infected cassava material (5, 7, and Bock, Guthrie, and Woods, unpublished data), but no virus like particles or mycoplasmalike bodies have been seen. This paper reports the first transmission of CMD by standard methods of mechanical inoculation of infected sap.Item Viruses Occurring in East Africa That are Related to Peanut Mottle Virus(1978) Bock, K.R.; Guthrie, E.J.; Meredith, G.; Overseas Development Ministry Crop Virology Project, East African Agriculture and Forestry Research Organization, P.O. Box 30148, Nairobi, KenyaViruses occurring in Cassia bicapsularis in Northern Tanzania, in Voandzeia subterranea in north western and eastern Tanzania, and in Phaseolus lunatus in the Kenya highlands, were all serologically related to peanut mottle virus. Their host ranges, and the symptoms they induced in test plants, were very similar, and they differed only in degree of virulence in some host species. The Voandzeia isolate did not infect groundnut, and only the Phaseolus isolate infected two species in the Cucurbitaceae. All the isolates infected Chenopodium amaranticolor, a species which formerly was reported as being immune to peanut mottle and thus considered of diagnostic value. In Africa, variation in peanut mottle virus isolates seems to be associated with host species and ecology, and there is at present no evidence for naturally occurring variants within a host species as occurs in groundnut in America. Three of the four isolates were purified by homogenising together infected leaf tissue, chloroform and 0.5 M sodium citrate buffer containing 1% 2-mercapto-ethanol at pH 8, in the proportion 1: 1:2 respectively, and precipitating the virus from the clarified homogenate with 5% w/v polyethylene glycol. When centrifuged in sucrose density gradients such preparations gave a single, bright specific light scattering zone with no haze.
