The effect of plant extracts as seed treatments to control bacterial leaf spot of tomato in Tanzania     

Ernest R. Mbega  Carmen N. Mortensen  Robert B. Mabagala  Ednar G. Wulff 《Journal of General Plant Pathology》2012,78(4):277-286

Bacterial leaf spot (BLS) caused by seed-borne xanthomonads is a serious disease of tomato (Solanum lycopersicum L.), causing significant losses in both yield and quality. To identify more effective control measures, we evaluated crude extracts from 84 plant species in in vitro and in planta assays for antibacterial activity against BLS of tomato. In the in vitro assays, 20.2?% of the tested plant extracts totally inhibited growth of bacteria when seed washings from treated seeds were plated on nutrient agar medium. In the in planta assays, 17.8?% of the tested plant extracts reduced BLS incidence by 100?% in tomato seedlings. The most effective seed treatments were obtained with extracts from Aloe vera, Betula pendula, Coffea arabica, Glycyrrhiza uralensis, Juniperus communis, Ocimum basilicum, Quercus robur, Rheum palmatum, Rosmarinus officinalis, Ruta graveolens, Sinapis alba, Yucca schidigera and Salvia officinalis. Seed treatment of tomato with these extracts completely inhibited Xanthomonas perforans in both in vitro and in planta assays. Extracts from A. vera, C. arabica and Y. schidigera were tested three times using tomato seeds of cultivars Tanya, Cal-J and Moneymaker in Tanzania. Treatment of tomato seeds with these extracts had a positive effect on the number of normal seeds and had no effect on seedling vigor, height and weight. These results indicate that plant extracts from A. vera, C. arabica and Y. schidigera are potential candidates for seed treatment against seed-borne xanthomonads of tomato in Tanzania.  相似文献   

Soil sulphur status following long-term annual application of animal manure and mineral fertilizers   总被引：1，自引：0，他引：1  

J. Eriksen  J. V. Mortensen 《Biology and Fertility of Soils》1999,28(4):416-421

 In agricultural systems with low S inputs, crops rely on the release of S from organic forms in the soil. In the Askov long-term experiments, started in 1894 on both sandy and loamy soils, soil S status following long-term application of animal manure and mineral fertilizers was investigated in the growing season of 1995. In a field trial with oil-seed rape (Brassica napus, L.) soil analysis, leaf tissue analysis, yield and S removal in plant material was used to characterize differences in availability of soil S. One half of all plots received 63 kg S ha^–1 as gypsum. Long-term fertilization with animal manure or NPK fertilizer increased the content of soil organic C in both soils and of organic S in the sandy soil compared with unfertilized plots. Although dry matter yields were unaffected, the S uptake in harvested crop parts increased considerably after S application. The amounts of N and S in harvested seeds and straw were closely related, but the N : S ratio decreased when S was applied. Soil and plant analyses both indicated that critical levels of S concentrations were reached, and that S application was capable of raising S concentrations well above the critical level. Because no additional mineralization from residual organic S took place, it was concluded that the residual S effect from long-term annual applications of animal manure or mineral fertilizers did not significantly increase the level of soil S available for crops with a short growing season, such as oil-seed rape. Received: 9 January 1998  相似文献   

Holding wild Snow crab,Chionoecetes opilio: effects of stocking density and feeding on survival and injury          下载免费PDF全文

Sten Ivar Siikavuopio  Philip James  Bjørn Ronald Olsen  Tor Evensen  Atle Mortensen  Stein Harris Olsen 《Aquaculture Research》2017,48(4):1590-1595

In this study the effects of different stocking densities on survival, injury and weight of captive male snow crab were examined. The first experiment (I) was carried out in square plastic tanks (700 L) with stocking densities of 100 (L), 150 (M) and 200 kg m^?3 (H) for 30 days. In a second experiment (II) snow crabs were kept at a stocking density of 50 kg m^?3 and were either fed (F) or not fed (S) for the same period of 35 days. The last experiment (III), was carried out with stocking densities of 25 kg m^?3 for 21 days with two groups, one with inactivated claw and one without rubber bands, with three replicates per treatment. In the first experiment mortality (H = 27, M = 26 and L = 36%) and occurrence of injuries (H = 27, M = 20 and L = 16%) were high in all groups. The weight loss during the experimental period was; H = 15.3, M = 10.9 and L = 15.5 g, and was not significant different between the groups. In experiment II the mortality (F = 13% and S = 14%) and injuries were lower (F = 12% and S = 17%). The average weight increased in the fed treatment and decreased in the starved treatments. In the last experiment there was no mortality in any of the groups and the levels of injury were low (5% and 7%). The results show that adult male snow crab cannot be stored at densities equal to or higher than 25 kg m^?3 for 3 weeks without risk of mortality.  相似文献   

Exercise lengthens the interovulatory interval in mares     

D.E. Kelley  J.R. Gibbons  S.E. Pratt  R.L. Smith  C.J. Mortensen 《Journal of Equine Veterinary Science》2009

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Autumn growth and cold hardening of winter wheat under simulated climate change     

Hans M. Hanslin  Leiv M. Mortensen 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(5):437-449

Abstract

Plant responses to elevated CO₂ are governed by temperature, and at low temperatures the beneficial effects of CO₂ may be lost. To document the responses of winter cereals grown under cold conditions at northern latitudes, autumn growth of winter wheat exposed to ambient and elevated levels of temperature (+2.5°C), CO₂ (+150 µmol mol^?1), and shade (?30%) was studied in open-top chambers under low light and at low temperatures. Throughout the experiment, temperature dominated plant responses, while the effects of CO₂ were marginal, except for a positive effect on root biomass. Increased temperature resulted in increased leaf area, total biomass, total root biomass, total stem biomass, and number of tillers, but also a lower content of total sugars and a weaker tolerance to frost. The loss of frost tolerance was related to the larger size of plants grown at elevated temperature. The 30% light reduction under shading did not affect the growth, sugar content, or frost tolerance of winter wheat. At the low temperatures found at high latitudes during autumn, the atmospheric CO₂ increase is unlikely to enhance autumn growth of winter wheat to any significant extent, while a temperature increase may have important and major effects on its development and growth.  相似文献   

Two-Year Weed Seedling Population Responses to a Post-Emergent Method of Site-Specific Weed Management     

Williams  Martin M.  Gerhards  Roland  Mortensen  David A. 《Precision Agriculture》2000,2(3):247-263

Field experiments were conducted to determine how a site-specific weed management practice in Zea mays L. influenced the numerical and spatial distribution of a naturally occurring weed infestation in Z. mays and the succeeding Beta vulgaris L. crop. Compared to conventional broadcast herbicide applications, site-specific herbicide applications reduced herbicide load by 11.5 and 98.0% in two separate Z. mays fields. The broad range in outcomes was attributed to the spatial aggregation and density of target weed populations. While herbicide use was successfully reduced at field locations with low weed density, most survivors of multiple control tactics were in locations with the highest initial density. A greater understanding of interactions between weed management and weed density would increase the likelihood that site-specific weed management offers long-term improvements over conventional approaches.  相似文献   

Effects of Ozone on Growth of Seven Grass and One Clover Species     

Leiv M. Mortensen 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(4):235-239

Abstract

Seven species of grass and one of red clover were grown at different ozone (O₃) concentrations for about five weeks in growth chambers located in a greenhouse. At an O₃ concentration of 55 compared with 10 nmol mol^?1 during 7 h day^?1 the shoot dry weight decreased by 45% in Phleum pratense, 28% in Dactylis glomerata and Poa pratensis, 23% in Festuca rubra and 16% in Festuca pratensis, while the effects on Agrostis tenuis were not significant. No effect was found at 25 compared with 10 nmol mol^?1O₃. Visible O₃ injury was observed in all six species at 55 nmol mol^?1 and this effect was generally well correlated with the effect on the dry weights. In another experiment no effect was found with O₃ concentrations of up to 62 nmol mol_?1 on Lolium perénne, while the dry weight in Trifolium pratense decreased by 30% at 59 compared with that at 6 nmol mol^?1.  相似文献   

Announcements     

W. Mortensen  O. Vahl 《Aquaculture (Amsterdam, Netherlands)》1979,18(1):73-76

A system which controls the amount of rations fed and the length of the feeding periods independently in each of six simultaneous experiments is described with circuit diagrams.  相似文献   

Light quality and growth of Norway spruce (Picea abies (L.))     

Leiv M. Mortensen  Martin Sandvik 《New Forests》1988,2(4):281-287

Seedling of Norway spruce (Picea abies L.) were grown under three different light qualities in fluid-roof growth chambers. Blue light with a high red/far-red ratio decreased shoot length as well as total plant dry weight compared to natural light. Yellow light with a low blue/red ratio did not significantly affect the plants. The effects of light quality were generally the same at 18, 24 and 28 °C day temperature. Plant growth was reduced at temperatures above 24 °C.  相似文献   

Characterizing the spatial pattern of Abutilon theophrasti seedling patches     

Dieleman  & Mortensen 《Weed Research》1999,39(6):455-467

Spatial biology of weed populations is the study of weed patches and their relevant patch-level processes. In this context, a patch was defined as an area in which individuals are aggregated into discrete subdivided populations. Four Abutilon theophrasti seedling patches in two continuous maize production fields were surveyed using a contiguous grid of quadrats between 1995 and 1997. Surveyed area was dependent on patch size and ranged from 96 m² to 1134 m². Within each area, all seedlings were counted in each 1 m × 0.75 m quadrat in June, just before post-emergence weed control, and in mid-July after all weed control practices were completed. The spatial pattern observed in the seedling distribution maps was single or multiple focal points of high seedling density that decreased with distance from the focal point. Two-directional correlograms corroborated this visual observation, such that A. theophrasti seedling density in neighbouring quadrats was spatially autocorrelated, and correlation strength decreased with distance separating quadrats. Autocorrelation coefficients decreased at a greater rate across crop rows than parallel to crop rows. Visually, patch shape was elliptical and oriented in the direction of field traffic. Factors affecting patch-level processes of spatial aggregation, stability and edge dynamics were considered.  相似文献