Liter Of Soil Research Articles

Study on the Rare Semiaquatic Plant Elatine hydropiper (Elatinaceae) in Lithuania: Population Density, Seed Bank and Conservation Challenges.

Wet, intermittently flooded freshwater coastal and shallow water habitats are notable for their high biodiversity. Many of the usually semiaquatic annuals or small perennials common in such habitats are in decline due to the high sensitivity of such habitats to changes caused by anthropogenic and natural factors. The Euro-Siberian semiaquatic Elatine hydropiper rarely occurs in Lithuania and is protected there and in other Baltic and Central European countries. In 2020, we found a large population of Elatine hydropiper in southern Lithuania (Varėna district) in Lake Pabezninkai and its exposed shores. The water level of the lake has receded by about 1.5-1.6 m since 2018, exposing wide, wet, and sandy or silty shores. The aim of this study was to determine the status of the Elatine hydropiper population and to assess its potential for long-term survival. The objectives of the study were to (a) determine the size and quantitative characteristics of the population, (b) assess the seed bank in the shallows and exposed shores of the lake, (c) assess the species diversity in the communities with Elatine hydropiper, (d) evaluate the conservation value of the studied species and the lake habitat. The studies were carried out between 2020 and 2021. The number and coverage of plant patches as well as seed bank studies were carried out at three sites with different shoreline substrate. At each site, the number of patches and coverage was assessed in 50 sample plots of 100 cm2. The seed bank was examined in the top 5 cm of the substrate. A total of 90 substrate samples were analyzed. We found that Elatine hydropiper grows on ca. 0.38 ha in the lake and on ca. 0.95 ha on the shores. On the exposed shores, the mean number of Elatine hydropiper patches per 1 m2 was 2155 ± 1241.5 and their mean cover was 23.17% of the surface. Seed bank analyses revealed that the seeds and seed shells were significantly more abundant in the bottom sediments than in the shore sand or silt. The mean number of seeds per liter of soil was 85.8 ± 210.2, and the mean number of seed shells was 217.0 ± 265.8. The assessment of the status of the species in Lithuania according to the IUCN (International Union for Conservation of Nature) criteria has led us to conclude that it should now be classified as vulnerable [A3; B1ab(iii); C2a(ii); D2]. The key to protecting Elatine hydropiper and other co-occurring rare species with similar ecological and biological characteristics, as well as the plant communities of shallows and exposed wet banks, is to protect their habitats. The survival of the species and their habitats could be assured by recurring significant water level fluctuations in the lake, resulting in periodic emergence of patches of wet sand or silt free from perennial vegetation.

Nutritional efficiency in phosphorus of arabica coffee genotypes

Nutritional efficiency is a term used to characterize plants in their capacity to uptake and use nutrients, being related to the efficiency of uptake, translocation and utilization of nutrients. Different coffee genotypes are expected to exhibit variability in their nutritional efficiency. This work aimed to evaluate the phosphorus nutritional efficiency in arabica coffee genotypes. The experiment was conducted in a greenhouse of the Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), located in the municipality of Lavras – Minas Gerais, Brazil. The experimental design was a randomized complete block design, in a 10x2 factorial scheme (10 arabica coffee genotypes and two dosages of phosphate fertilization), with four replications. Each experimental plot consisted of one pot with ten liters of soil, with one plant. The cultivars Catiguá MG2, MGS Ametista and Sarchimor MG 8840 are neither efficient nor responsive to phosphate fertilization. Progeny H 6-47-10 pl. 3 and the cultivar Catuaí Vermelho IAC 144 are not efficient but are responsive to phosphate fertilization. The cultivars Paraíso MG H 419-1, Topázio MG 1190 and MGS Paraíso 2 are efficient but are not responsive to phosphate fertilization. The cultivars Bourbon Amarelo IAC J10 and MGS Aranãs are efficient and responsive to phosphate fertilization. Index terms: Coffea arabica; Cultivars; Mineral nutrition.

Plant growth promoting Rhizobacteria: Increase of vegetative and roots biomass in Portulacaria afra

In this study, the ability of PGPRs to improve the growth and rooting of Portulacaria afra in pots was evaluated. Portulacaria afra is an interesting plant from a medicinal and ornamental point of view, but it shows some difficulties in the early stages of cultivation. The two experimental groups in cultivation were: i) group without beneficial micro-organisms (CTRL) (peat 60% + pumice 30% + chabazite 10%), irrigated with water and substrate previously fertilized; ii) group with beneficial micro-organisms (PGPR) (peat 60% + pumice 30% + chabazite 10%), irrigated with water and substrate previously fertilized, (1,5g TNC Bactorr S13 per litre of soil). The microorganisms in TNC S13 Bactorr were: Bacillus amyloliquefaciens, B. brevis, B. cirulans, B. coagulans, B. firmus, B. halodenitrificans, B. laterosporus, B. licheniformis, B. megaterium, B. mycoides, B. pasteuri, B. polymixa, B. subtilis (1.3 x 1011 cfu/Kg). All plants treated with Plant Growth Promoting Rhizobacteria (PGPR) showed a significant increase in the agronomic parameters analysed compared to the untreated control (CTRL), both in Portulacaria afra and in Portulacaria afra variegated. The results show that microorganisms are able to improve the absorption of water and nutrients by increasing the agronomic and physiological characteristics of plants. Very interesting aspects to improve agronomic quality, especially for those who cultivate plants from particular environments and that are poorly adapted to our climates and cultivation methods.

Soil fumigation with mustard essential oil to control bacterial wilt in tomato

In vitro experiments showed that six isolates, belonging to different biovars, were equally susceptible to mustard essential oil (MEO) vapor. The proportion of cell mortality and colony growth inhibition were directly related to the dose of MEO. A 24 h exposure to 1 or 2 μL of AITC per liter of box volume resulted in mortality of 89% and 92% of cells, respectively, and exposure to 10 μL L−1 resulted in 100% cell mortality. The growth of developing colonies was reduced by 89% at 2 or 4 μL L−1 and by 96% at 6 or 10 μL L−1. The leakage of intracellular materials increased with increasing doses of MEO vapor. The decline in soil inoculum density by fumigation was directly related to the MEO dose. The initial inoculum density of approximately 3 × 105 colony-forming units per gram of soil declined by 67, 91 and 96% at fumigation doses of 25, 50 and 75 μL of allyl isothiocyanate (AITC) per liter of soil, respectively. The pathogen was not detected at a fumigation dose of 100 μL L−1. Disease control was also related to the fumigation dose. After 48 days, the bacterial wilt symptoms did not develop on the tomatoes when the soil was fumigated at 100 μL L−1 or higher.

Leaf area estimation of cassava from linear dimensions.

The objective of this study was to determine predictor models of leaf area of ​​cassava from linear leaf measurements. The experiment was carried out in greenhouse in the municipality of Botucatu, São Paulo state, Brazil. The stem cuttings with 5-7 nodes of the cultivar IAC 576-70 were planted in boxes filled with about 320 liters of soil, keeping soil moisture at field capacity, monitored by puncturing tensiometers. At 80 days after planting, 140 leaves were randomly collected from the top, middle third and base of cassava plants. We evaluated the length and width of the central lobe of leaves, number of lobes and leaf area. The measurements of leaf areas were correlated with the length and width of the central lobe and the number of lobes of the leaves, and adjusted to polynomial and multiple regression models. The linear function that used the length of the central lobe LA = -69.91114 + 15.06462L and linear multiple functions LA = -69.9188 + 15.5102L + 0.0197726K - 0.0768998J or LA = -69.9346 + 15.0106L + 0.188931K - 0.0264323H are suitable models to estimate leaf area of ​​cassava cultivar IAC 576-70.

Host location success of root-feeding nematodes in patches that differ in size and quality: A belowground release-recapture experiment

Resource patch size and patch nutritional quality are both important factors influencing local densities of herbivores. The responses of herbivores to resource patch size have been mostly studied in aboveground plant–insect interactions, whereas belowground organisms have received little attention. We studied responses of different root-feeding nematode species associated with marram grass (Ammophila arenaria (L.) Link) to resource patch size and quality. Different nematode species were released in experimental mesocosms filled with dune sand in which we established marram grass patches of varying sizes. Half of the patches of small, medium and large size were fertilized to test if immigration probabilities of nematodes depended on patch quality. We tested the hypotheses that (1) nematodes should aggregate on larger patches and (2) colonization of patches would also depend on patch nutritional quality, with higher nematode recapture rates expected in fertilized patches. Two species (Helicotylenchus pseudorobustus, Hemicycliophora thornei) of the five released species were recaptured in the experiment. The fraction of nematodes immigrating into the rhizosphere of a plant patch increased with patch size (i.e. root biomass), which was in line with predictions of the Resource Concentration Hypothesis. When fractions were recalculated to represent recapture rates per liter of soil, recapture rates of nematodes did not differ among patch sizes, indicating that the increase in recapture rates was directly proportional to the increase in patch size. This suggests that the process through which nematodes located patches was not distinguishable from a random process where entering patches is based on random encounters with patch boundaries. In contrast to our expectation, fertilization had a strong negative effect on patch responses of both nematode species. Our study represents an approach that may be used to explore whether belowground biota behave in similar ways as aboveground biota, in order to determine how perceived differences in environments affect ecological interactions.

Use of Logistic Equation for Detection of the Initial Parasitism Phase of Egyptian Broomrape (Phelipanche aegyptiaca) in Tomato

The dynamics of the host–parasite relationship between tomato cv. Brigade and Egyptian broomrape is temperature-related. This relationship was utilized for the development of an equation on the basis of thermal time (as measured by growing degree days, GDD, C) to predict the parasitism dynamics of Egyptian broomrape in tomato. To obtain a reliable prediction from thermal time values, studies based on a wide range of temperatures are essential. Four temperature-regime treatments and five levels of infestation with Egyptian broomrape seeds were tested in a multiclimate greenhouse (phytotron) and a temperature-controlled greenhouse, respectively. The day/night temperature regimes were 20/12 C, 23/15 C, 26/18 C, and 29/21 C and the infestation levels were 0 (noninfested control), 1, 5, 10, and 25 mg of Egyptian broomrape seeds per liter of soil. As expected, increasing temperature or infestation levels resulted in faster appearance and higher rate of attachments, respectively. The relation between development of attachments and GDD was described as a three-parameter logistic curve. In both temperature-regime and infestation-level experiments, the development of attachments began 200 GDD after planting and the maximal number of attachments was recorded 800 GDD after planting. A significant reduction in the aboveground biomass of the tomato plants due to increased Egyptian broomrape biomass was recorded only for the 26/18 C and 29/21 C day/night treatments and the three highest infestation levels (5, 10, and 25 mg L−1soil). The ability to predict the start of parasitism can be used to develop a climate-based system for Egyptian broomrape control with herbicides.

Seletividade do oxyfluorfen para a cultura do pinhão-manso

Realizou-se um experimento para avaliar a seletividade do oxyfluorfen para a cultura do pinhão-manso. Foi utilizado o delineamento experimental inteiramente casualizado, com cinco repetições, em esquema fatorial 2 x 2 + 1, sendo duas doses do herbicida (600 e 1.200 g ha-1 do ingrediente ativo), dois modos de aplicação (sobre a planta e sobre o solo) e uma testemunha sem aplicação do herbicida. Após o transplante das mudas para vasos plásticos com 10 litros de solo, os tratamentos foram aplicados com o auxílio de um balde. O oxyfluorfen, quando aplicado sobre as plantas, mostrou-se tóxico nas duas doses testadas, sendo observados sintomas mais intensos nos primeiros dias após a aplicação dos tratamentos. Após esse período, as mudas recuperaram o vigor e surgiram novas brotações que não apresentavam sintomas de toxicidade. Esses sintomas consistiram de manchas esbranquiçadas nas folhas, que evoluíram para necrose. Nas mudas em que o herbicida foi aplicado no solo, não foram observados sintomas visuais de toxicidade. Observou-se redução na massa fresca e seca das folhas quando 600 g ha-1 do herbicida foram aplicados sobre a planta ou 1.200 g ha-1 sobre o solo. Contudo, a área foliar e o número de folhas não diferiram significativamente entre as doses utilizadas e os modos de aplicação. Das quatro espécies daninhas semeadas (Brachiaria decumbens, Brachiaria plantaginea, Sida rhombifolia e Bidens pilosa), apenas Bidens pilosa não foi controlada pelo oxyfluorfen aplicado em pré-emergência.

RESISTÊNCIA DE CULTIVARES DE BRÁSSICAS À HÉRNIA DAS CRUCÍFERAS

A hérnia das crucíferas causada por Plasmodiophora brassicae ocasiona sérios danos à cultura das brássicas. O presente trabalho teve como objetivo avaliar a resistência de cultivares de brássicas a hérnia das crucíferas. Foram utilizados 45 cultivares comercializadas de repolho, brócolos, couve-manteiga, couve-flor e couve-chinesa. A parcela experimental foi constituída de um vaso de alumínio com capacidade para três litros de solo contendo duas plantas, com quatro repetições. Em cada vaso foram aplicados dois gramas de galhas trituradas, na forma de rega. Aos 60 dias foram avaliadas a severidade da doença no sistema radicular e a massa fresca da parte aérea, verificando os efeitos sobre as cultivares de cada espécie avaliada. Utilizou-se o programa SASM-Agri e o teste Scott-Knott a 5% de probabilidade para a análise dos dados. A severidade de galhas foi menor nos ‘Híbrido Kukai 70’ e ‘65’ de couve-chinesa e ‘Bola de Neve‘ de couveflor. A massa fresca da parte aérea entre cultivares de mesma espécie foi maior para ‘Ramoso Piracicaba’; ‘Ramono Santana’; ‘Pirate’; ‘Vida Sul’; ‘Flórida’ e ‘Condor’ para brócolos, ‘Híbrido Kukai 70’ e ‘Híbrido Kukai 65’ para couve-chinesa e ‘HíbridoMatsukaze’ para repolho. Entre as cultivares testadas quanto à resistência ao isolado de P. brassicae, o ‘Híbrido Kukai 70’ e ‘65’ de couve-chinesa e ‘Bola de Neve‘ de couve-flor comportaram-se como os mais resistentes.

First Report of Root and Collar Rot by Phytophthora cryptogea on Sweet Cherry in Italy.

Sweet cherry (Prunus avium L.) cultivation has increased in Italy and ≈30,000 ha are now in production. In the spring of 2006, a disease survey was conducted in orchards of central Italy. Decline symptoms of Prunus avium 'Durone' grafted on wild rootstocks of Prunus avium consisted of reduced tree vigor, yellowing of leaves, and development of root and collar rot. A reddish brown discoloration of the inner bark and wood was observed on symptomatic trees. Symptoms were recorded in three cherry orchards seasonally submitted to soil saturation conditions. In one orchard, symptoms were observed on approximately 30% of 170 surveyed trees. A Phytophthora species was consistently isolated on PARPH-V8 medium (2) from collar lesions of five cherry trees over nine trees randomly chosen among symptomatic trees in the three orchards. Colonies (20) were isolated and all appeared fluffy on potato dextrose agar and did not grow at 35°C. The morphological characteristics fit the descriptions of Phytophthora cryptogea Pethybr. & Lafferty (1). Sequence analysis of the internal transcribed spacers region of isolates shared 100% homology with P. cryptogea (GenBank Accession Nos. EF418948.1, EF418943.1, and EF153671.1). Pathogenicity of two P. cryptogea isolates (AN1 and AN2, Accession Nos. EF661576 and EF661577, respectively) was tested by soil infestation in a growth chamber at 22°C using 15 1-year-old rooted seedlings of wild rootstock of Prunus avium for each isolate. Noninoculated seedlings (15) were used as negative controls. The inoculum was produced by growing isolates on autoclaved millet grains moistened with V8 juice for 4 weeks. Each plant was inoculated with 30 cm3 of inoculum per liter of soil. Each seedling was randomly assigned to isolates AN1, AN2, or the noninoculated control and arranged in a complete random design. All plants were flooded for 24 h every 2 weeks for 8 weeks. At the end of the experiment, all inoculated seedlings showed crown wilting and root rot. Control plants showed no symptoms. Percentage of necrotic lateral roots expressed as dry weight (±SE) was 19.9 ± 0.6, 17.5 ± 0.2, and 4.4 ± 0.5, respectively, for seedlings inoculated with isolates AN1, AN2, and controls (analysis of variance F = 7.48, P < 0.01). Values of inoculated seedlings were significantly different from the control plants with the Tukey Post-Hoc test. No difference in virulence was observed between the two isolates. P. cryptogea was always reisolated from the roots of inoculated plants. Although pathogenicity of P. cryptogea on sweet cherry has been reported in the United States and other European countries (3,4), to our knowledge, this is the first record of P. cryptogea on sweet cherry orchards in Italy. The presence of P. cryptogea in cherry orchards is of significant concern because of its aggressiveness to this host and woody hosts such as apple, apricot, peach, walnut, and kiwi.

Testing of potato varieties to assess resistance to Globodera rostochiensis and Globodera pallida

Testing of potato varieties to assess resistance to <i>Globodera rostochiensis</i> and <i>Globodera pallida</i>

First Report of Damping-Off of Wild Rice in California Caused by Pythium torulosum.

During 1994, damping-off of wild rice (Zizania palustris L.) in a single field in eastern Shasta County, CA resulted in near total stand failure. Since then, the disease was observed in at least 11 other fields with varying levels of stand loss. In all cases, the affected wild rice was grown as a volunteer crop following one or more years of wild rice production. Symptoms included a dark red discoloration and necrosis of the primary root followed by seedling death. When the red discoloration was limited to secondary roots, the plants often survived. Pythium torulosum, readily recovered from symptomatic roots by isolation on PARP media, was identified by morphological structures produced on grass blades in water (homothallic with smooth-walled oogonia, plerotic oospores, monoclinous antheridia, and inflated filamentous sporangia) and a 99.2% internal transcribed spacer sequence similarity of the rDNA (1). To complete Koch's postulates, inoculum of two isolates of P. torulosum grown on moistened cornmeal/sand (2%/98% [v/v]) for 3 weeks at 25°C were combined and mixed into sterilized sandy loam soil at a rate of 30 cm3 inoculum per liter of soil. Sterilized noninfested soil was used as a control treatment. Twenty wild rice seeds (cv. Franklin) were sown in each of four replicate 20-cm-diameter pots in each treatment. Plants were submerged in water and maintained in a greenhouse at 18 to 25°C. After 8 weeks, plants stands were reduced 50% in infested pots; dry weights of infected plants were reduced by 45% relative to the controls. The fungus was reisolated from symptomatic plants but not from the plants grown in noninfested soil. The experiment was repeated with similar results. To our knowledge, this is the first report of damping-off of wild rice caused by P. torulosum. Reference: (1) C. A. Levesque and W. A. M. DeCock. Mycol. Res. 108:1363, 2004.

Potential of sucrose and Pennisetum purpureum cv. Cameroon mulch on the management of Meloidogyne javanica and M. incognita

The effects of sucrose on motility and infectiveness of juveniles of Meloidogyne javanica were evaluated under laboratory and greenhouse conditions, using brown sugar and crystal sugar. Results showed that crystal and brown sugar solutions reduced motility and promoted morphological alterations of juvenile nematodes in vitro. The increasing dosages of sucrose reduced the number of galls and egg masses in tomato root by reducing the number of infective juveniles. The efficiency of granular sucrose, sucrose solution, with and without elephant-grass mulch, in the reduction of reproduction and final population of M. incognita race 2, were also evaluated. Granular sucrose induced decrease on the numbers of galls and eggs masses per root system as well as on juveniles in the soil. For sucrose solution assay, the best results for reproductive reduction were obtained with 300g of granular sucrose per liter of soil, applied at seven days intervals, associated with elephant-grass mulch.

Aplicação do fomesafen via água de irrigação por aspersão no controle de Euphorbia heterophylla

A aplicação de herbicidas via água de irrigação (herbigação) por aspersão, especialmente por pivô central, vem crescendo no Brasil. O objetivo deste estudo foi investigar a eficácia de doses de fomesafen aplicado via água de irrigação por aspersão no controle de Euphorbia heterophylla. Os tratamentos foram dispostos no esquema fatorial (4 x 3 x 2) + 3, sendo quatro doses do fomesafen (60, 120, 180 e 240 g ha-1), três estádios de desenvolvimento de E. heterophylla (1, 7 e 14 dias após a emergência - DAE), dois métodos de aplicação (pulverização e herbigação) e testemunhas sem herbicida (uma para cada estádio de desenvolvimento da planta daninha). Foi empregado o delineamento inteiramente casualizado, com quatro repetições. Cada unidade experimental constou de um vaso com 4,0 L de solo, onde foram distribuídas 50 sementes dessa planta daninha. A pulverização foi feita com 200 L ha-1 de calda; na herbigação foi usada lâmina de água de 4,72 mm, aplicada por simulador de irrigação. E. heterophylla foi mais suscetível ao fomesafen com 1 DAE. Neste estádio, a herbigação controlou-a melhor que a pulverização nas doses de 180 e 240 g ha-1. Na aplicação aos 7 DAE, geralmente a pulverização foi mais eficaz que a herbigação, mas o controle da planta daninha não foi satisfatório. Aplicado com 14 DAE, o herbicida, independentemente da dose e do método de aplicação, proporcionou controle pobre ou nenhum.

An image-based deformation measurement system for the geotechnical centrifuge

New techniques of image capture and analysis have been recently applied to geotechnical centrifuge modelling. These techniques improve the utility of the geotechnical centrifuge by increasing the detail and precision of deformation measurements. This paper describes the use of a simple image-based deformation measurement system on a drum centrifuge. Precise deformation fields comprising many thousands of measurement points can be evaluated from images of plane strain tests using small soil models typically comprising 2 litres of soil. Digital still photography is used to capture high resolution images. A weighted shutter allows a continuous sequence of images to be captured without the need for an onboard PC or communication with the camera via sliprings. Particle Image Velocimetry (PIV) and close range photogrammetry are used to process the resulting images. Target markers are not needed since PIV operates on the spatial variation in image brightness to measure displacement. Close range photogrammetry allows image distortion to be corrected. Distortion leads to a 5% variation in image scale (or pixel size) for this test geometry. An example test of a skirted strip foundation under eccentric vertical load is analysed. The instantaneous velocity field at failure is manipulated to allow the realism of simple upper bound failure mechanisms to be examined. It is interesting to note that although the measured failure load matches almost exactly the optimal upper bound solution, the observed deformation mechanism differs significantly.

Exsolution of nitrogen and argon by methanogenesis in Dutch ground water

Dutch ground water was sampled under high pressure in stainless steel vessels and analysed by gas chromatography for Ar, N 2, CH 4 and O 2. Results show a deficit N 2 and Ar concentrations combined with a high CH 4 concentration that are attributed to the occurrence of exsolution of Ar and N 2 during methanogenesis (the focus of this article). They also show N 2 and Ar in concentrations exceeding the concentration in equilibrium with atmospheric air that are caused by the entrapment and subsequent (partial) dissolution of excess air; in recent ground water, N 2 excesses also are caused by denitrification. phreeqc model runs of methanogenesis at different pressures, with different amounts of organic matter decomposition and different amounts of initial dissolved N 2 show five features. Firstly, methanogenesis under lower hydrostatic pressures causes more N 2 and Ar exsolution than methanogenesis under higher hydrostatic pressures. Secondly, when little organic matter is decomposed (e.g. 1 mmol/l), the value taken for the fixed total pressure (between 1.05 and 3.0 atm.) influences mostly the N 2 and Ar concentration, and when much organic matter is decomposed (e.g. 16 mmol/l), the value taken for the fixed total pressure influences mostly the CH 4 concentration. Thirdly, in order to explain the observed gas concentrations, not more than 27 mmol of organic matter should be decomposed per litre of soil. Fourthly, the phreeqc run with initial denitrification (initial N 2 pressure=1.0 atm.) fits the data better than the phreeqc run without initial denitrification. Fifthly, the maximum total pressure of bubble formation is 3.0 atm. Analysed gas concentration profiles show that the greatest source of CH 4 is found up to approximately 20 m below surface. However, samples with CH 4 partial pressures >0.25 atm. were found up to a maximum average sampling screen depth of 81 m below surface.

Efeito de doses e tipos de compostos orgânicos na produção de alface em dois solos sob ambiente protegido

Avaliou-se o efeito de três doses de composto orgânico de três composições distintas, aplicados em dois solos [Latossolo Vermelho Escuro, textura arenosa (LE) e Areia Quartzoza (AQ)], na produção e absorção de nutrientes pela planta de alface. Conduziu-se de 02/07 a 27/08/1997 um experimento dentro de túnel plástico, pertencente à UNESP, em Botucatu, em vaso plástico, contendo quatro quilos de solo. Os solos foram corrigidos para atingirem saturação por base de 80% e todos os vasos receberam adubação fosfatada (150 mg de P kg-1 de solo), potássica (100 mg de K kg-1 de solo) e micronutrientes. Os compostos foram misturados aos solos nas quantidades de 60; 120 e 240 g de composto por vaso. Os três compostos foram originados a partir de casca de eucalipto, serragem de madeira e palhada de feijão, misturados com esterco de aves. O experimento foi realizado em delineamento inteiramente casualizado, em três repetições, com vinte tratamentos em esquema fatorial (3 doses x 3 compostos x 2 solos) mais um tratamento testemunha para cada solo (ausência de composto orgânico). O composto de palhada de feijão aumentou a biomassa fresca da parte aérea e a quantidade de N, K, Ca, Mg, B, Cu, Fe e Zn nas plantas de alface. Para o P e Mn o composto de palhada de feijão diferiu significativamente apenas em relação ao composto de casca de eucalipto. Em todas as características avaliadas no LE houve melhores respostas da cultura em relação ao AQ. Quanto às dosagens utilizadas, as diferenças foram observadas somente nos tratamentos com palhada de feijão, onde as maiores dosagens propiciaram o aumento de biomassa fresca e seca da parte aérea, e nas quantidades de macro e micronutrientes.

Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility

Greenhouse studies were conducted to assess the intensity of smooth pigweed and common purslane aboveground interference (AI) and belowground interference (BI) with lettuce and to determine primary mechanisms of interference of each species as affected by P fertility rates. Lettuce was transplanted in mixtures with either smooth pigweed or common purslane according to four partitioning regimes: no interference, full interference, BI, and AI. Soil used was low in P for optimum lettuce yields, therefore P was added at rates of 0, 0.4, and 0.8 grams of P per liter of soil. Shoot and root biomass and plant height were measured for each species, as well as P tissue content. The data obtained indicated that smooth pigweed interfered with lettuce primarily through light interception by its taller canopy. A secondary mechanism of interference was the absorption of P from the soil through luxury consumption, increasing the P tissue content without enhancing smooth pigweed biomass accumulation. In contrast, common purslane competed aggressively with lettuce for P. Because the weed grew taller than lettuce, light interception was a secondary interference factor.

Effects of Plant Essential Oils on Ralstonia solanacearum Population Density and Bacterial Wilt Incidence in Tomato.

Greenhouse experiments were conducted to determine the effectiveness of plant essential oils as soil fumigants to manage bacterial wilt (caused by Ralstonia solanacearum) in tomato. Potting mixture ("soil") infested with R. solanacearum was treated with the essential oils at 400 mg or μl and 700 mg or μl per liter of soil in greenhouse experiments. R. solanacearum population densities were determined just before and 7 days after treatment. Populations declined to undetectable levels in thymol, palmarosa oil, and lemongrass oil treatments at both concentrations, whereas tea tree oil had no effect. Tomato seedlings transplanted in soil treated with 700 mg/liter of thymol, 700 ml/liter of palmarosa oil, and 700 ml/liter of lemongrass oil were free from bacterial wilt and 100% of plants in thymol treatments were free of R. solanacearum. Soil amendment with fresh leaves of essential oil-producing plants did not reduce bacterial wilt incidence compare to untreated inoculated control. Some thyme oil-producing plants such as thyme (Thymus vulgaris) cv. German winter, Creeping thyme (Thymus serpyllum), and Greek oregano (Origanum vulgare subsp. hirtum), while remaining symptomless, became systemically infected by R. solanacearum and were therefore identified as hosts of R. solanacearum.

First Report of the Cyst Nematode (Globodera tabacum) Complex on Flue-Cured Tobacco in Spain.

The Globodera tabacum complex infects tobacco (Nicotiana tabacum L.) fields in the United States. In August 2001, plants of flue-cured tobacco cv. K326 from a field of the La Vera Region of Spain displayed a premature wilting and yellowing of foliage, but the roots looked healthy. In the laboratory under the microscope, nematode cysts were observed on the roots. At harvest in September 2001, soil and root samples were collected to identify the nematode and to quantify the population in the soil. Identification of the nematode was based on morphological characteristics of second-stage juveniles collected from cysts and perineal patterns of cysts recovered from the roots (2). Cysts were collected from roots, and second-stage juveniles were extracted from crushed cysts. The nematode population was extracted from the soil and quantified as described by Barker (1). The nematode population was identified as Globodera tabacum. Soil density of the nematode was 5,307 cysts per liter of soil, 64,286 eggs per liter of soil, and 16,071 second-stage juveniles per liter of soil. To our knowledge, this is the first report of G. tabacum complex in Spain.