Root Immersion Research Articles

Ácidos orgânicos no controle da murcha bacteriana do pimentão

The effect of disinfectant organic acids on the control of bacterial wilt of sweet pepper (Capsicum annuum L.) caused by Ralstonia solanacearum (Smith) Yabuuchi et al. was evaluated. The in vitro sensitivity of bacteria to the ascorbic, citric and lactic (0.25, 0.5, 1, 2.5, 5 and 10%) acids and the stable mixture of the ascorbic (1%), citric (0.475%) and lactic (0.475%) acids (0.4, 0.8, 2.5, 5, 10 and 100%) (v/v) was evaluated. After the phytotoxicity test the 0.8% stable mixture and ascorbic, citric and lactic acids 1% were selected and tested for bacterial wilt severity reduction, by root immersion or shoot spraying. The pathogen was inoculated by wounding roots and deposition of the inoculum. In vitro, R. solanacearum showed high sensitivity to lactic acid 10% and medium sensitivity to lactic acid (5 and 2.5%), ascorbic and citric acids 10% and stable mixture 100%. All treatments applied by root immersion significantly increased the incubation period (IP) and reduced the area under the disease progress curve (AUDPC), mainly lactic acid 1% (100%). The citric and lactic acids 1% and stable mixture 0.8% also increased IP and reduced AUDPC until 46.1% when applied by shoot spraying.

Application of positron emission tomography and 2-[18F]fluoro-2-deoxy-d-glucose for visualization and quantification of solute transport in plant tissues

AbstractThe aim of the presented work was to evaluate the uptake and distribution of 2-fluoro-2-deoxy-d-glucose spiked with 18F (2-[18F]FDG) in tissues of tobacco plants (Nicotiana tabacum L.) by positron emission tomography and multivariate data analysis after the immersion of the petiole of excised leaf or root of a tobacco plant in a glucose solution. From individual experiments it was found that increasing glucose concentration (c glu) in the applied solution resulted in significantly higher 2-[18F]FDG diffusion and translocation within the leaf parenchyma. More than a four times increase of the 2-[18F]FDG translocation into the aboveground parts of the tobacco plant in case of the root immersion in solution with 100-times higher c glu in comparison with the control (c glu = 0.00762 mg cm−3) was determined. These facts were not confirmed only visually on basis of the obtained 3D images, but also by the increasing coincidence transfer factor (TFc) values defined by the ratio of the number of analyzed coincidences in the non-immersed parts of leaf or plant to coincidences in leaf petiole or root immersed in the solution. Cluster and principal component analysis suggest that the 2-[18F]FDG uptake by the petiole of excised leaf and root system was realized by different mechanisms; also, the 3D image quality is influenced by the initial radioactivity of the applied solution.

Sobrevivência e crescimento inicial de pinhão-manso em função da época de plantio e do uso de hidrogel

http://dx.doi.org/10.5902/1980509810560O trabalho objetivou comparar o efeito do uso do hidrogel e da época de plantio sobre a sobrevivência e o crescimento inicial de Jatropha curcas L. nas condições do oeste do Paraná. O experimento foi conduzido em Pato Bragado, PR, durante 2008 e 2009. Os tratamentos compreenderam o plantio de mudas de três procedências de pinhão-manso (Pedro J. Caballero, Nova Porteirinha e Janaúba) submetidas ou não à imersão do sistema radicular no ato do plantio em hidrogel previamente hidratado na concentração de 5,0 g L-1 em diferentes épocas de plantio (primavera, verão, outono e inverno). O delineamento experimental foi em blocos casualizados, arranjados em esquema de parcelas subdivididas com cinco repetições para cada época de plantio. Após o período de noventa dias, quantificou-se o efeito do polímero sobre a porcentagem de sobrevivência e o crescimento inicial por meio dos incrementos em altura e diâmetro do coleto, número de folhas, área foliar, área média da folha e área foliar específica, sendo as médias comparadas pelo teste Tukey a 5%. Os resultados indicaram que a imersão das raízes em hidrogel aumentou a porcentagem de sobrevivência das mudas no plantio da primavera em 6,7%. O uso do hidrogel não propiciou ganhos no crescimento das mudas de pinhão-manso, prejudicando o crescimento no plantio do inverno. Contudo, maiores incrementos foram obtidos no plantio da primavera. As procedências Pedro J. Caballero e Nova Porteirinha externaram maior capacidade de resposta ao desenvolvimento pós-plantio para as diferentes épocas de plantio.

Enantioselective Uptake and Translocation of a Novel Chiral Neonicotinoid Insecticide Cycloxaprid in Youdonger (Brassica campestris subsp. Chinensis)

For a novel potential commercial chiral pesticide, an independent study on the fate characteristics and residues of each stereoisomer is essential if the application rates for the pesticide and human exposure are to be reduced. The absorption and translocation behavior of a chiral insecticide, cycloxaprid, in plants treated by root immersion and blade smearing was studied using (14)C-labeling tracer techniques. With the root treatment, total absorption of (1R;8S)-cycloxaprid (RS) (12.39%) was much greater than that of (1S;8R)-cycloxaprid (SR) (3.31%) at 192 h after treatment (HAT). The mass concentrations (RS/SR) of cycloxaprid in the roots, cotyledons, leaf 1, leaf 2, and leaf 3 were 37.0/16.8, 8.3/2.8, 11.7/6.5, 5.1/4.8, and 8.0/4.7 mg kg(-1) (fresh weight), respectively, at 192 HAT at an initial concentration 1.6 mg kg(-1). With the foliar application treatment, no significant difference was observed between the total absorption of RS (3.11%) and SR (4.03%) at the end of the treatment. Both acropetal and basipetal transport of absorbed (14)C occurred and more than 71.83% of absorbed RS and 82.42% of SR remained in the treated leaf. Stereoselective absorption was observed during root uptake but not during foliar absorption.

Sobrevivência e crescimento do pinhão-manso em função do método de aplicação e formulações de hidrogel

O trabalho comparou o efeito de formulações e métodos de aplicação de hidrogel no plantio sobre a sobrevivência e crescimento inicial de mudas de pinhão-manso (Jatropha curcas L.). O ensaio foi conduzido em Pato Bragado, PR, durante os anos de 2009 e 2010. O delineamento experimental foi em blocos casualizados, em arranjo fatorial 5 x 2, compreendendo cinco formulações de hidrogel (0,0; 2,5; 5,0; 7,5 e 10,0 g L-1) e dois métodos de aplicação (imersão do sistema radicular em hidrogel previamente hidratado e aplicação de 0,5 L diretamente na cova). As variáveis analisadas incluíram a porcentagem de sobrevivência, o incremento na altura e no diâmetro do coleto e o número de ramificações quantificadas aos três meses e dezoito meses do plantio. Após três meses do plantio a análise revelou efeitos das diferentes formulações, com ajuste linear para sobrevivência, em ambos os métodos de aplicação. Para os incrementos na altura e no diâmetro do coleto houve ajuste polinomial quadrático para a aplicação de 0,5 L cova-1. Após dezoito meses do plantio não foram observados efeitos significativos (p > 0,05) para os métodos de aplicação ou formulações de hidrogel. O uso da formulação 7,0 g L-1 de hidrogel aplicado diretamente na cova com volume de 0,5 L cova-1 aumentou o sucesso do estabelecimento do povoamento de pinhão-manso e formulações acima da sugerida reduziram o crescimento das mudas, nas condições do oeste do Paraná.

Effects of sea level rise on mangrove Avicennia population growth, colonization and establishment: Evidence from a field survey and greenhouse manipulation experiment

Mangroves will either face longer tidal inundation or retreat landwards in response to on-going accelerated sea level rise. However, little is known about the growth, regeneration or colonization of mangrove seedlings under the different tidal inundation regimes associated with accelerated sea level rise. In the present study, a field survey and a greenhouse mesocosm experiment were conducted to evaluate possible effects of accelerated sea level rise on colonization, establishment and seedling growth of a mangrove pioneer species, Avicennia marina. Avicennia populations at different elevations of the intertidal zone on Xiamen Island in Fujian Province, China showed distinctive patterns in both seedling density and plant age. The seedlings at lower elevations had less annual biomass accumulation and population productivity, but higher shoot to root ratios, suggesting that elevation has positive effects on seedling growth. The greenhouse mesocosm experiment with 1-year-old A. marina seedlings utilized five inundation periods (0, 2, 4, 6 and 12 h in a semidiurnal tidal cycle) and two inundation depths (root immersion and canopy immersion). Both inundation period and depth exerted significant and negative effects on biomass accumulation, photosynthetic rate, leaf electron transportation and water use efficiency. However, the negative effects of canopy immersion were more profound than root immersion. Canopy immersion exacerbated the effects of prolonged inundation, with no seedlings surviving under canopy immersion at the 12-hour treatment. These results suggest that at lower elevations with higher sea level, canopy immersion will have greater negative effects on seedling colonization, establishment and early growth of A. marina. This finding is instrumental in predicting the future dynamics of mangrove forests under increasing sea levels.

수삼의 탄산칼슘용액 침지에 따른 물성 변화

This study investigated the textural changes after the calcium-pectin bonding of ginseng roots and their vinegar and calcium solution immersion. The strength and breakdown of the ginseng roots increased according to the increase in the calcium carbonate concentration, with the highest in the 0.7~1.0% calcium carbonate. The hardest and softest ginseng roots were obtained in the 1.0% calcium carbonate concentration. The strength, brittleness and hardness of the ginseng roots that were soaked in 1% calcium carbonate and 5~6% acidity vinegar continued to increase with the long-term storage of the ginseng root drink. The softness of the ginseng root that was dipped in 5% acidity vinegar with 1.0% calcium carbonate decreased with the long-term storage of the ginseng root drink. Thus, calcium and vinegar immersion of ginseng roots could prevent softening and clouding during the long-term storage of the ginseng root drink.

Comparison of the effects of flooding vs. low-oxygen gas on pea (Pisum sativum L. cv. 'Alaska') primary roots

Flooding reduces soil oxygen necessary for root growth. In some mesophytes low levels of oxygen are mitigated by the formation of aerenchyma or expansion of intercellular spaces. But root immersion in water may have effects on roots in addition to reducing oxygen levels. At temperatures >15°C Pisum sativum primary roots develop cavities in the centers of their vascular cylinders in response to saturated or flooded conditions. In the present study we compared the response of flooded pea roots to their response to hypoxia without flooding by using an innovative system that allows separation of the gas environment of a root system from that of its shoot system. Seedlings were flooded after 4 d growth and compared to seedlings in unflooded medium and to seedlings in the gas-manipulation experiment. At 25°C in slightly moist vermiculite, roots 4 d after planting were exposed to a gas mixture with 10.5% oxygen and shoots to 20.5% oxygen and compared to normoxic controls. Oxygen levels in all containers were monitored, root growth was measured, and frequency and size of vascular cavities were determined for all treatments. Under flooding and low-oxygen gas, root growth was suppressed and vascular cavity frequency was strongly enhanced compared to controls. Significant differences in root growth responses were not seen between these differing hypoxic conditions, but low-oxygen gas caused larger cavities than flooding, which suggests flooding with water may have subtle effects different than simple hypoxia.

First Report of Verticillium Wilt Caused by Verticillium dahliae on Mango Trees (Mangifera indica) in Southern Spain.

Verticillium wilt, primarily caused by Verticillium dahliae Klebahn and V. albo-atrum Reinke & Berthold, affects a wide range of economically important crops. This disease is an increasing problem in areas where young mango trees are planted on land previously planted in vegetable crops. In 2008, symptoms of Verticillium wilt were observed in mango cvs. Kent and Osteen in the subtropical fruit-producing area of Málaga in southern Spain. In a new mango grove of cv. Kent, previously planted in potatoes and tomatoes, ~20% of 200 1-year-old trees had one-sided branch dieback. In many of these trees the symptoms expanded, leading to decline and eventual death. Cross sections of affected branches revealed brown vascular discoloration. Verticillium was isolated from surface-sterilized segments of symptomatic branches placed on acidic potato dextrose agar (PDA). Plates were incubated at 24°C. After 3 days, slow-growing colonies were transferred to PDA. Verticillium was similarly isolated from symptomatic potato plants grown in a nearby field. Identification of V. dahliae was initially based on morphology and further confirmed by molecular methods. All isolates tested produced microsclerotia, a defining feature that distinguishes V. dahliae from V. albo-atrum. For molecular characterization, V. dahliae specific primers 19 and 22 (1) and universal primers ITS1 and ITS4, which amplify the rRNA internal transcribed spacer (ITS) region (4), were used. Bands of expected size were amplified with both primer combinations. ITS fragments were sequenced and identical to the V. dahliae reference sequence (GenBank AY555948) (3). Pathogenicity assays were conducted with a selected isolate from mango using tomato plants from the susceptible line 'Moneymaker' and the near isogenic 'Motabo' line carrying the Ve gene conferring resistance to race 1 isolates. Five 1-month-old plants (four-leaf stage) were inoculated by root immersion in a suspension of 107 conidia/ml. Five control plants were mock inoculated with distilled water. As a positive control, five plants were inoculated with the previously described race 1 strain Dvd-T5 (2), which induces severe symptoms in susceptible tomato cultivars. Symptoms were scored visually at various time points up to 40 days by a 0 to 5 scale in which 0 = negligible chlorosis or wilting, 1 = chlorosis and wilting and/or curling in individual leaves, 2 = necrosis in leaves, 3 = at least one branch dead, 4 = wilt and/or chlorosis in upper leaves and/or two or more branches dead, and 5 = plant dead or all leaves and most of stem necrotic. The isolate from mango caused typical Verticillium wilt symptoms with a mean disease rating of 3.6 at 40 days postinoculation in both lines. The mean disease rating for Dvd-T5 in Moneymaker 40 days postinoculation was 4.0. V. dahliae was reisolated from symptomatic plants but not from noninoculated controls. To our knowledge, this is the first report of Verticillium wilt on mango in Spain. More problems with Verticillium wilt are expected because of the increasing planting of mango in fields previously dedicated to horticultural crops.

Estratégias para eficiência da seleção de feijoeiro quanto à resistência à murcha-de-fusário

O objetivo deste trabalho foi melhorar a eficiência de seleção de linhagens de feijoeiro, para a resistência ao Fusarium oxysporum f.sp. phaseoli. Foram comparados sete métodos de inoculação do patógeno, em quatro linhagens de feijoeiro, em delineamento inteiramente ao acaso, em esquema fatorial 4x7, com cinco repetições. A reação das linhagens foi avaliada aos 21 dias após a inoculação. Para identificar a melhor época de avaliação da severidade do patógeno, 18 linhagens de feijoeiro foram submetidas à inoculação do patógeno, pela imersão de raízes na suspensão de esporos, com corte do sistema radicular, em delineamento inteiramente ao acaso, com 15 repetições. O progresso da doença foi acompanhado aos 7, 14, 21 e 28 dias após a inoculação. Com dados de experimento de 20 linhagens de feijoeiro com 15 repetições, foi simulado o efeito do número de repetições, que variou de 5 a 15. Os métodos que melhor discriminaram as linhagens foram os de imersão de raízes na suspensão de conídios - com ou sem o corte do sistema radicular. As avaliações da reação à doença devem ser realizadas com pelo menos 21 dias após a inoculação. Cinco repetições são suficientes para classificar as linhagens de feijoeiro, quanto à resistência à murcha-de-fusário.

Marcação de fitomassa de cana-de-açúcar com aplicação de solução de uréia marcada com15N

O objetivo deste trabalho foi comparar três métodos de aplicação de solução de uréia marcada com15N (15N-uréia ): pulverização foliar, injeção na base do colmo e imersão radicular, a fim de se definir qual seria o mais eficiente na marcação de fitomassa de cana-de-açúcar. O experimento foi instalado na Estação Experimental Apta - Pólo Regional Centro Sul, em Piracicaba, SP. A cana-de-açúcar, variedade SP80 3280, foi plantada em vasos preenchidos com aproximadamente 120 dm³ de Neossolo Quartzarênico de textura arenosa. O delineamento experimental foi inteiramente casualizado, com quatro repetições. A fitomassa de cana-de-açúcar dos três tratamentos, no 11º mês de desenvolvimento, não diferiu estatisticamente, e suas abundâncias de 15N foram superiores à natural, tendo-se verificado a seguinte ordem decrescente de marcação com 15N: parte aérea > rizoma > rizomas+raízes na camada de 0,0-0,2 m > raízes na camada de 0,2-0,4 m > raízes em profundidade maior que 0,4 m. Entre os métodos de aplicação de 15N-uréia, a injeção na base de colmos é o de mais fácil execução, o mais efetivo na marcação da fitomassa e o que apresentou a maior recuperação do traçador (96%). A aplicação foliar é comparável à injeção, somente na marcação e na recuperação do traçador no sistema radicular.

First Record of Verticillium dahliae on Potato in Malta.

Potato is an important and highly valued crop throughout the Maltese Archipelago. Much of the production is exported to Holland. In January 2005, minor wilts and chlorosis of potato plants were observed in a field at Hal-Farrug, Luqa (Malta). Verticillium dahliae Kleb (1) was isolated on potato dextrose agar (PDA) from vascular tissue excised from the base of the plants. Three different isolates were obtained, all of which were typically distinguished by verticillately shaped conidiophores and the abundant production of microsclerotia on PDA. In May 2005, colonies of these three isolates were cultured in potato dextrose broth (PDB), from which conidial suspensions of each isolate were prepared with sterile distilled water to a concentration of 107 ml-1. For each isolate, 10 7-day-old potato seedlings were inoculated via root immersion in the inoculum suspension and transplanted to 20-cm diameter plastic pots containing a soil/peat mixture (1:1 [v/v]). Seedlings treated in the same way with sterile distilled water were used as a control. All plants were kept under controlled glasshouse conditions (20 ± 3°C) and watered to field capacity as required. Minor chlorosis and wilt of the pair of lower-most leaves was noted 7 days after inoculation. During subsequent weeks, wilt began to appear in the typical half-leaf form, while chlorosis was noted on all organs of the plants, including the principal stem (3). Symptoms were absent on the control plants. Measuring the weight of the new tubers produced by each plant revealed no apparent difference between inoculated and healthy plants; nevertheless, inoculated plants resulted in more tubers with a smaller diameter in respect to those of the uninoculated plants. V. dahliae was never isolated from tubers. Little to no variation in symptom severity was noted among plants inoculated with the three individual isolates. At the end of June, V. dahliae was reisolated on PDA from all inoculated plants, in particular, from vascular tissues originating from principal and lateral stems, crowns, and roots. All attempts to isolate the pathogen from control plants were unsuccessful. Molecular detection of the pathogen by using species-specific primers and real-time Scorpion PCR (2) confirmed the results obtained by the classical isolation method. The low symptom severity observed by the growers in the field, usually mistaken for normal dieback of aged plants, might explain why V. dahliae was never reported before on potatoes in the Maltese Archipelago.

The role of salicylic acid in defense response of tomato to root-knot nematodes

Salicylic acid (SA) is involved in hypersensitive reactions of plants to incompatible pathogens and in systemic acquired resistance (SAR) after the attack of necrosis-inducing pests. The possible involvement of SA in defense responses of tomato to root-knot nematodes ( Meloidogyne spp., RKNs) was investigated. SA was found not to be responsible for the inhibition of catalase (CAT) detected in the early stages of Meloidogyne-tomato incompatible interactions. CAT extracted from leaves was inhibited only after treatment of the seedlings with SA concentrations as high as 4 mM. Most of the amount of free SA found in plants after SA treatment was detected in the leaves. SA (0.2 mM) was found to cause a competitive inhibition of CAT only at high substrate (H 2O 2) concentrations. Under different conditions it did not affect, or even enhanced, the enzyme activity. Therefore, it is suggested that SA-mediated CAT inhibition does not operate early in resistance against RKN in tomato, although it might have a role in the consequent lesion formation. Plant uptake of SA was detected by immersion of roots of 1-month-old seedlings in aqueous solutions of SA and SA plus a soil humic acid. Considering the low level of free SA retained by roots, the capacity of exogenously provided SA to act as an elicitor of resistance to root pests is considered unlikely.

An Experimental Inoculation System to Study Citrus-Xylella fastidiosa Interactions.

Difficulties in reproducing the citrus variegated chlorosis (CVC) disease symptoms in experimental plants have delayed implementation of studies to better understand the essential aspects of this important disease. In an extensive study, cultivars of sweet orange (Citrus sinensis) were inoculated with Xylella fastidiosa using procedures that included root immersion, and stem absorption, pricking, or infiltration of the inoculum into plants of different ages. Inoculum consisted of 5-day-old cultures or cell suspensions of CVC strain 9a5c diluted in phosphate-buffered saline. Inoculated plants and controls were grown, or transferred just after inoculation, to 5-liter pots or 72-cell foam trays. Approximately 4, 5, 9, and 12 months after inoculation, leaves were collected and processed for polymerase chain reaction analysis or X. fastidiosa isolation on BCYE agar medium. Root immersion and stem inoculation of 4- and 6-month-old plants resulted in low percentages of symptomatic (0 to 7%) and plants positive by isolation (0 to 9%). Pinpricked or injected stems of 1-month-old seedlings resulted in high percentages of plants symptomatic (29 and 90% in Pera Rio, 75, 59, and 83% in Valencia, and 77% in Natal) or positive by isolation (26 and 93% in Pera Rio, 98, 96, and 83% in Valencia, and 77% in Natal). In foam trays, the seedlings grew less, the incubation period was shorter, and disease severity was higher than in pots. This system allows testing of higher numbers of plants in a reduced space with a more precise reproduction of the experimental conditions.

Biological Control of Damping-Off of Tomato Seedlings and Cucumber Phomopsis Root Rot by Bacillus subtilis RB14-C

Bacillus subtilis RB14-C, which is a streptomycin resistant mutant of B. subtilis RB14 isolated from compost, produces an antifungal peptide, iturin A, and was evaluated for its suppressive ability against damping-off of tomato seedlings and Phomopsis root rot of cucumber. In damping-off disease of tomato seedlings caused by Rhizoctonia solani, RB14-C cell suspension treatment did not suppress the disease occurrence whereas germinated seed treatment of the RB14-C cells reduced the occurrence of the damping-off. In both treatments, iturin A could not be detected from the treated soil. In the Pho- mopsis root rot of cucumber, root immersion treatment of cucumber seedlings with RB14-C cell sus- pension at the time of transplanting effectively suppressed the root rot, resulting in growth recovery 50 days after the treatment even though the initial growth was retarded due to the Phomopsis infection. These results suggest that germinated seed treatment of RB14-C cells and root immersion treatment with RB14-C cell suspension can be applied as promising biological control practices of the damping- off of tomato seedlings and the cucumber Phomopsis root rot, respectively.

Applied environmental stresses to enhance the levels of polyphenolics in leaves of hawthorn plants.

In this investigation, two species of Crataegus (hawthorn) were chosen because their polyphenolic constituents have recently received greater attention for the treatment of patients with severe heart disease. One-year-old plants of hawthorn (Crataegus laevigata and C. monogyna) were subjected to water-deficit (continuous water deprivation), cold (4 degrees C), flooding (immersion of roots of plants in water) or herbivory (leaf removal) stress treatments (each of 10 days duration) in order to assess their effects on levels of polyphenolics, namely (-)-epicatechin, catechin, chlorogenic acid, vitexin, vitexin-2"-O-rhamnoside, acetylvitexin-2"-O-rhamnoside, hyperoside, quercetin, and rutin in the leaves. The working hypothesis followed is that one or more of these stress treatment will elicit increases in the levels of these polyphenolics. Cold stress causes increases in levels of vitexin-2"-O-rhamnoside, acetylvitexin-2"-O-rhamnoside, hyperoside, and quercetin in both Crataegus species. Water-deficit stress increased the productivity of chlorogenic acid, catechin, and (-)-epicatechin in both hawthorn species. Flooding and herbivory caused no net increases, and in some cases, decreases in levels of polyphenolics. These studies indicate that either water-deficit stress or cold stress treatments, or a combination of the two, can be used to enhance the levels of desired polyphenolics in the leaves of these two hawthorn species in a photobioreactor system. These results may have significance for hawthorn in adapting to water-deficit or cold stress and are important considerations for the use of hawthorn in the treatment of heart disease in humans.

Vascular colonization patterns in susceptible and resistant tomato cultivars inoculated with Fusarium oxysporum f.sp. lycopersici races 0 and 1

The vascular colonization pattern of Fusarium oxysporum f.sp. lycopersici races 0 and 1 in tomato was studied in five susceptible and five resistant cultivar–fungus combinations during a 26‐day period after inoculation by root immersion. Propagules spread discontinuously along the stems in all five cultivars 1 day after inoculation, irrespective of cultivar resistance. Five days later the fungus was limited to the stem bases in all cultivars. Between the fifth and 12th days, stem colonization by the fungus stopped in all cultivar–race combinations. Thereafter, the situation remained stable in resistant combinations, with inoculum distributed discontinuously, and no disease symptoms were apparent. By contrast, in the susceptible combinations a gradual upward colonization of the stems was seen such that fungal distribution was no longer discontinuous and disease symptoms appeared. These results suggest that a fungal ‘incubation’ period in the base of the vascular system is required before a secondary invasion of tissues occurs in susceptible genotypes. The slope of the regression line fitted between the height reached by the fungus up the stem (y) and the time after inoculation (x) provides a measure of the horizontal (polygenic) resistance in tomato cultivars

Interaction of Cytokinins and Abscisic Acid During Regulation of Stomatal Opening in Bean Leaves

Effects of benzyladenine (BA) and abscisic acid (ABA) applied separately or simultaneously on parameters of gas exchange of Phaseolus vulgaris L. leaves were studied. In the first two experimental sets) 100 μM ABA and 10 μM BA were applied to plants sufficiently supplied with water. Spraying of leaves with ABA decreased stomatal conductance (gs) and in consequence transpiration rate (E) and net photosynthetic rate (PN) already 1 h after application, but 24 h after application the effect almost disappeared. 10 μM BA slightly decreased gas exchange parameters, but in simultaneous application with ABA reversed the effect of ABA. Immersion of roots into the same solutions markedly decreased gas exchange parameters and 24 h after ABA application the stomata were completely closed. The effect of ABA was ameliorated by simultaneous BA application, particularly after 1-h treatment. In the third experimental set, plants were pre-treated by immersing roots into water, 1 μM BA, or 100 μM ABA for 24 h and then the halves of split root system were dipped into different combinations of 1 μM BA, 100 μM ABA, and water. In plants pre-treated with ABA all gas exchange parameters were small and they did not differ in plants treated with H2O+H2O, H2O+BA, or BA+BA. In plants pre-treated with BA or H2O, markedly lower values of PN were found when both halves of roots were immersed in ABA. Further, the effects of pre-treatment of plants with water, 1 μM BA, 100 μM ABA, or ABA+BA on the development of water stress induced by cessation of watering and on the recovery after rehydration were followed. ABA markedly decreased gas exchange parameters at the beginning of the experiment, but in its later phase the effect was compensated by delay in development of water stress. BA also delayed development of water stress and increased PN in water-stressed leaves. BA reversed the effect of ABA at mild water stress. Positive effects of BA and ABA pre-treatments were observed also after rehydration.

Efficacy of three 15 N labelling techniques for estimating below-ground N in Sesbania rostrata

Three 15N labelling strategies for estimating below-ground N in Sesbania rostrata grown in pots under flooded conditions were examined. The estimated proportions of total plant N resident below-ground were 13% (stem injection), 42% (leaf immersion) and 56% (adventitious root feeding). The average estimate based on leaf and root immersion (49%) was considered to be realistic on the basis of published literature with other foliar labelled legumes, while root and root-derived N appeared to be underestimated by stem injection.

UTILIZAÇÃO DE DOIS MÉTODOS DE INOCULAÇÃO NA AVALIAÇÃO DA RESISTÊNCIA DE CULTIVARES E LINHAGENS DE FEIJOEIRO A Fusarium oxysporum F. SP. phaseoli

Este trabalho foi conduzido com o objetivo de comparar a eficiência de dois métodos de inoculação na avaliação da resistência de plantas de feijoeiro a Fusarium oxysporum f. sp. phaseoli. Avaliou-se a reação de 16 cultivares e linhagens, incluindo padrões de resistência e suscetibilidade à doença. Num dos métodos, o plantio foi realizado em solo tratado com brometo de metila (CH3Br). As plantas foram inoculadas através do método de perfuração do solo, que consistiu na aplicação de 10m<img SRC="http:/img/fbpe/cr/v32n1/a01img01.gif"> de suspensão de conídios ao redor das plantas, previamente feridas. No outro método utilizado, denominado método de imersão de raízes, as plantas obtidas em areia lavada e aquecida (60ºC - 30min) foram retiradas e lavadas em água corrente e cortadas em cerca de 01cm do sistema radicular, o qual foi imerso em suspensão de conídios por 05 minutos. As plantas foram então replantadas em vasos contendo solo tratado com brometo de metila. Em ambos os métodos de inoculação, as plantas estavam com 07 dias de germinação, sendo inoculadas com a suspensão de inóculo a uma concentração de 1 x 10(6) conídios/m<img SRC="http:/img/fbpe/cr/v32n1/a01img01.gif">. As plantas controle sofreram o mesmo tratamento, referente ao método de inoculação correspondente. O experimento foi delineado inteiramente ao acaso, em parcelas subdivididas, com 04 repetições por tratamento, sendo o método de inoculação locado na parcela principal e as cultivares e linhagens nas subparcelas. Cada repetição foi constituída por 01 vaso com 04 plantas. As avaliações foram realizadas aos 15, 20, 25 e 30 dias após a inoculação, baseadas em escala de notas, com 9 graus de infecção, proposta pelo CIAT. Os dados obtidos foram transformados para índice de doença de Mackinney. Observou-se uma maior eficiência do método de imersão das raízes, na avaliação da resistência do feijoeiro a murcha de Fusarium, evidenciando os genótipos Goiano precoce, RH 3104 e IPA-9 como resistentes, e LM 93204247, LM 93204296 e IPA-1 como suscetíveis.