Growth Of Lettuce Seedlings Research Articles

Biostimulant properties of cyanobacterial hydrolysate related to polyamines

Developing new and natural sources of plant growth promotors is essential to ensure the safe and sustainable production of vegetables for human consumption. In recent years, the potential of microalgae as plant biostimulants has been investigated. Arthrospira platensis (Spirulina platensis) biomass is a recognized protein source and its enzymatic hydrolysis contains molecules such as polyamines with potential to promote plant growth. Therefore, the aim of the present study was to investigate the biostimulant properties of hydrolyzed biomass of A. platensis. Bioassays were performed to determine auxin-like and cytokinin-like bioactivity of the hydrolysates. In addition, its effect on lettuce seedling growth was investigated and an organic system field trail performed where yield and free polyamine levels in leaves quantified. The hydrolysates had a cytokinin-like effect in the bioassay. Foliar applications promoted the growth of lettuce seedlings with the 4-h reaction hydrolysate (Sph4) being the most effective at promoting growth and increasing the spermine content by 64% in the lettuce leaves. The polyamine concentration was also compared in non-hydrolyzed A. platensis and Sph4. Hydrolysis resulted in a 34% increase in spermine content. It was concluded that Sph4 is a natural plant growth promoter that can be used as a raw material for biostimulants, and spermine could be an active compound and a metabolic indicator of Sph4 bioactivity.

Influence of phosphate on phytotoxicity of ceria nanoparticles in an agar medium

Fate and toxicity of manufactured nanoparticles (NPs) in the living organisms and the environment are highly related to their transformation. In the present study, the effect of phosphate on the phytotoxicity and transformation of CeO2 NPs was investigated in an agar medium using head lettuce plants that are sensitive to Ce3+ ions. Plants were treated by CeO2 NPs with or without phosphate for 10 days. Results suggest that the treatments of P deficiency (P(-)) and CeO2 NPs (P(+)&Ce) could separately induce significant inhibition on the growth of lettuce seedlings and cause oxidative stress, but the inhibition was the most serious when the two conditions were combined (P(-)&Ce). In the absence of phosphate, more CeO2 NPs were transformed to Ce(III) in the roots and more Ce3+ ions were translocated to the shoots, which induced higher toxicity to head lettuce. Phosphates could alleviate the phytotoxic effect of CeO2 NPs through the precipitation of dissociated Ce3+ ions. Considering the wide existence of phosphate in the environment, phosphate-related transformation may be a critical factor in evaluating the toxicity and fate of many other metal-based NPs.

<i>In Vitro</i> Bioassay of Allelopathy in Four Bamboo Species; <i>Bambusa multiplex, Phyllostachys bambusoides, P. nigra, Sasa kurilensis</i>, Using Sandwich Method and Protoplast Co-Culture Method with Digital Image Analysis

Moderately strong allelopathic activities were found in four bamboo species, Bambusa multiplex cv. Houraichiku; Phyllostachys bambusoides cv. Madake; P. nigra cv. Hachiku; Sasa kurilensis cv. Chishimazasa, which are of different classification or of different ecological distributions, using the “Sandwich Method”, which assays the dried leaves on growth of lettuce seedlings. Only small difference of activity was found among the four bamboo species. In addition, “Protoplast Co-culture Method” for assay of allelopathy in a 50 μL liquid medium using a 96 well culture plate, was applied to the suspension cultures of the four bamboo species. Protoplasts were isolated from two-week cultured suspension cells of four bamboo species using Cellulase RS and Pectolyase Y-23 in 0.6 M mannitol. At low protoplast densities of bamboo, B. multiplex and P. bambusoides stimulated the recipient lettuce growth, i.e., non-spherically cell enlargement and cell divisions observed under an inverted microscope, while protoplasts of P. nigra and S. kurilensis were less stimulatory or inhibitory. Inhibitory effect of S. kurilensis was the strongest among four bamboo species. Furthermore, highly inhibitory effects of S. kurilensis protoplasts on yellow color accumulation of lettuce protoplasts were clearly observed by analysis of a scanned digital image of a 96-well culture plate. Differences and causes of the allelopathic activities were discussed comparing with other plant species studied using the same assay methods.

Plant growth promotion by Bradyrhizobium japonicum under heavy metal stress

The increase in usage of heavy metals in different industrial activities causes their existence in effluents. Excessive concentrations of these heavy metals pollute soil and water. Heavy metals cause toxicities and other harmful effects not only in humans and animals but also in plants and soil microorganisms. Heavy metals disrupt many biochemical and physiological activities in bacteria, including growth, development, enzyme and hormone production. Indole acetic acid (IAA) is one of the most important hormones in plants, which is secreted by both bacteria and plants. The present study assessed the effects of Ni, Pb and Cu on the growth of Bradyrhizobium japonicum and IAA production.B. japonicum were grown in yeast mannitol broth in a rotary shaker at 100rpm for 18h for each variant. Ni, Pb and Cu with concentrations ranging from 2.5–40mg/L were added to B. japonicum cultures and turbidity was measured at 600nm. Effects of Ni, Pb and Cu on IAA production were determined by measuring the IAA content with Salkowski method. The metal uptake by B. japonicum was determined in the range of 5–50mg/L. A lettuce seedling assay was conducted to observe the effect of B. japonicum on plant growth under heavy metal stress. Lettuce seedlings inoculated with the bacterium were spiked with 5–500mg/L of Ni, Pb and Cu. Shoot and root length, and plant dry biomass were measured after 5days of germination.Bacterial growth was reduced with the increase of Ni and Cu concentrations. However, there was no significant growth effect with Pb in the considered range. The IAA production also followed the same pattern with Pb and Ni, but in the presence of Cu, IAA content was slightly increased and reached an equilibrium. The growth retardations observed in lettuce in the presence of Pb, Ni and Cu were in the decreasing order of Ni>Cu>Pb. Bacterial inoculation reduced the heavy metal stress and increased the shoot and root lengths of lettuce seedlings. FTIR spectrum of the bacterial biomass showed that amine and nitro groups are responsible in metal sorption process. The Pb-treated bacterial biomass showed a considerable difference in the FTIR spectrum compared to other treatments. According to our results, B. japonicum is sensitive to heavy metal stress with a retardation of growth and IAA production, though it is able to enhance the growth of lettuce seedlings under heavy metal stress.

Effects of Stabilized Nanoparticles of Copper, Zinc, Manganese, and Iron Oxides in Low Concentrations on Lettuce (Lactuca sativa) Seed Germination: Nanotoxicants or Nanonutrients?

Information on the phytotoxicity of nanoparticles (NPs) at low concentrations (e.g., ppb to low ppm) is scarce. Therefore, this study was conducted to assess the effects of laboratory-prepared Cu, Zn, Mn, and Fe oxide NPs in low concentrations (<50 ppm) on the germination of lettuce (Lactuca sativa) seeds in a water medium. The data showed that CuO NPs were slightly more toxic than Cu ions while the toxicity of ZnO NPs was similar to that of Zn ions, and MnOx NPs and FeOx NPs were not only less toxic than their ionic counterparts but also significantly stimulated the growth of lettuce seedlings by 12–54 %. This study showed that manufactured NPs were not always more toxic than other chemical species containing the same elements. Instead, Mn or Fe NPs can significantly enhance plant growth and have the potential to be effective nanofertilizers for increasing agronomic productivity.

The uptake kinetics of NH4+ and NO3− by lettuce seedlings under hypobaric and hypoxic conditions

The objective of this study was to investigate how hypobaria and hypoxia affect the uptake kinetics of NH4+ and NO3− by lettuce (Lactuca sativa L. cv. Rome). Lettuce seedlings were grown in Erlenmeyer flasks containing NH4+ and NO3− solutions at seven concentrations (0.05–2.0mmoll−1) for 10h under 101 and 30kPa of total atmospheric pressures (TP) and 21, 6, and 2kPa of O2 partial pressures (pO2), respectively. Compared with 21kPa pO2, hypoxia (6 and 2kPa pO2) not only significantly inhibited the uptake of NH4+ or NO3− by lettuce seedlings, but also decreased the values ​​of maximum uptake rate (Vmax), Michaelis constant (Km), and Vmax/Km of NH4+ or NO3− uptake and the relative growth rate (RGR) as well as the N content of lettuce seedlings grown in NH4+ solution under two levels of TP. However, the N content of lettuce seedlings grown in NO3− solution was reduced under 30kPa TP. Under hypoxic conditions (6 and 2kPa pO2), hypobaria (30kPa) markedly enhanced the absorption of NH4+ and NO3− by lettuce seedlings, and increased the values ​​of Vmax and Vmax/Km of NH4+ and NO3− uptake as well as the value of Km in NH4+ uptake by improving O2 supply to the roots of lettuce seedlings. However, the value of Km for NO3− uptake decreased under the same conditions. The velocity of NO3− uptake by lettuce seedlings was higher than that of NH4+ under 101kPa TP and 21kPa pO2 conditions. The adverse effect of hypoxia (6 and 2kPa pO2) on NO3− uptake by lettuce seedlings was greater than that on NH4+ uptake under two levels of TP. The present study indicated that the uptake of NH4+ and NO3− and the growth of lettuce seedlings were improved by 30kPa hypobaria under the same pO2.

Angelicin as the Principal Allelochemical in Heracleum sosnowskyi Fruit

Distribution patterns of furocoumarins in fruits of the invasive species Heracleum sosnowskyi Manden. (Sosnowskyi's hogweed) during a cold stratification period were investigated. Angelicin, bergapten, methoxalen and imperatorin were mainly localized in the fruit coats and their content varied depending on the fruit source. Cold stratification treatment (90 days, 2-3 degrees C) reduced the content of furocoumarins in the fruit coats by more than two times, compared with those before stratification. The specific activity of the detected furocoumarins and total activity of crude extracts were evaluated using Lactuca sativa, as acceptor plant. Crude extracts obtained from fruit coats and seeds of H. sosnowskyi suppressed 50% of radicle and hypocotyl growth of lettuce seedlings at the concentration range of 1.0-1.7 mg/mL. The inhibitory activity of angelicin was proved to be the highest compared with the other tested furocoumarins, and the inhibitory activity of crude extracts could be explained mainly by the presence of angelicin. Both, monocots (Lolium multiflorum, Phleum pratensis, Festuca pratesis, Lolium perenne) and dicots (Tripholium repens, Trifolium pretense) were found to be sensitive to the exudates of whole H. sosnowskyi fruits. Thus, we assume, that high inhibitory potential of furocoumarins, especially angelicin, at high seed productivity of H. sosnowskyi might have an ecological significance in plant-plant interaction.

Wpływ szczepów bakterii wyizolowanych z hydroponicznej uprawy sałaty (Lactuca sativa L.) na wzrost siewek sałaty, rosnących w obecnosci rożnych form pożywienia azotowego [Influence of bacterial strains isolated from hydroponic cultures of lettuce (Lactuca sativa L.) on the growth of lettuce seedlings growing in the presence of various forms of nitrogen nutrition

320 bacterial strains isolated from the surface of cultivated plants, as well as from other parts of hydroponic cultures showed stimulating (49 bacterial strains) or inhibitory (9 bacterial strains) properties in respect to the investigated plant. The following bacteria were isolated: &lt;i&gt;Pseudomonas, Flavobacterium, Agrobacterium, Achromobacter&lt;/i&gt; and &lt;i&gt;Chromobacterium&lt;/i&gt;. The effects of active bacterial strains on the growth of seedlings were investigated in dependence on the kind of inorganic form of nitrogen present in the nutrient solutions. The same bacterial strains exerted a stimulating effect on seedlings growing on nitrates, weaker stimulation was observed in cultures with ammonium nitrate; the growth of lettuce seedlings on nutrient solution with ammonium only, was, as a rule, inhibited by the bacteria.

Screening and identification of phytotoxic volatile compounds in medicinal plants and characterizations of a selected compound, eucarvone.

Screening and identification of phytotoxic volatile compounds were performed using 71 medicinal plant species to find new natural compounds, and the characterization of the promising compound was investigated to understand the mode of action. The volatile compounds from Asarum sieboldii Miq. showed the strongest inhibitory effect on the hypocotyl growth of lettuce seedlings (Lactuca sativa L.cv. Great Lakes 366), followed by those from Schizonepeta tenuifolia Briquet and Zanthoxylum piperitum (L.) DC.. Gas chromatography-mass spectrometry (GC/MS) identified four volatile compounds, α-pinene (2,6,6-trimethylbicyclo[3.1.1]hept-2-ene), β-pinene (6,6-dimethyl-2-methylenebicyclo[3.1.1]heptane), 3-carene (3,7,7-trimethylbicyclo[4.1.0]hept-3-ene), and eucarvone (2,6,6-trimethy-2,4-cycloheptadien-1-one), from A. sieboldii, and three volatile compounds, limonene (1-methyl-4-(1-methylethenyl)-cyclohexene), menthone (5-methyl-2-(propan-2-yl)cyclohexan-1-one), and pulegone (5-methyl-2-propan-2-ylidenecyclohexan-1-one), from S. tenuifolia. Among these volatile compounds, eucarvone, menthone, and pulegone exhibited strong inhibitory effects on both the root and shoot growth of lettuce seedlings. Eucarvone-induced growth inhibition was species-selective. Cell death, the generation of reactive oxygen species (ROS), and lipid peroxidation were induced in susceptible finger millet seedlings by eucarvone treatment, whereas this compound (≤158μM) did not cause the increase of lipid peroxidation and ROS production in tolerant maize. The results of the present study show that eucarvone can have strong phytotoxic activity, which may be due to ROS overproduction and subsequent oxidative damage in finger millet seedlings.

Response of lettuce seedlings fertilized with fish effluent to Azospirillum brasilense inoculation

The continuous use of agrochemical inputs in modern agriculture for better crop productivity has resulted in unexpected environmental impact. This issue has raised public interest in exploring environmental friendly sustainable practices. In this study, three strains of Azospirillum brasilense (Sp7, Sp7-S and Sp245) were evaluated for their impacts on the growth of lettuce seedlings grown with fish effluent (FE) as a source of nutrients. Lettuce seeds were inoculated with these strains before sowing and at transplanting, and grown under greenhouse condition with natural light. Despite the existing indigenous microflora and low level of nutrients in the FE, the A. brasilense strains survived at populations ranging from 5 to 6 cfu g− 1 of roots and altered important agronomic traits, which led to growth enhancement. In particular, inoculated seedlings showed significant increase in the number of leaves, seedling height and root length. Chlorophyll and protein content were also improved, but only with Sp7 strain. However, the expression of pathogenesis-related protein, i.e., peroxidase, and level of endogenous indole-3-acetic acid increased by more than 50% in response to inoculation with the strains. Azospirillum inoculation also showed little or no adverse impact on the FE bacterial community indicating that it can be incorporated into a system that uses FE as a nutrient source, e.g., aquaponics. Thus, A. brasilense could be a valuable agent to help maximize the usefulness of FE or wastewater from freshwater aquaculture to further support plant growth.

Spent Mushroom Compost as a Substrate for the Production of Lettuce Seedlings

The successful production of marketable lettuce heads with full exploitation of the genetic potential of a particular cultivar depends on the availability of seedlings of the highest quality. The aims of the present study were (i) to evaluate the effects of substrates containing different proportions of spent mushroom compost on the growth of lettuce seedlings, and (ii) to determine the enduring effects of substrates containing spent mushroom substrate on the vigor of mature lettuce plants derived from such seedlings. The substrates employed in the germination and development of lettuce seedlings were obtained by mixing spent compost from the cultivation of Agaricus subrufescens and commercial vegetable substrate in different proportions. Seedlings were evaluated with respect to the number of leaves and the height, fresh mass and dry mass of the aerial parts, while mature plants were appraised according to stem height and circumference, fresh mass and dry mass of the lettuce head. Substrate containing between 42 to 48% spent mushroom substrate provided the most adequate conditions for the growth and development of crisphead lettuce seedlings and, consequently, of vigorous marketable plants. Under such conditions, the fresh mass of the aerial parts of seedlings attained a level of 0.89 g plant-1, while the fresh mass of the marketable heads achieved a maximum of 233.45 g plant-1. The data presented herein verify that top quality lettuce seedlings yield high quality marketable heads, and that quality improvement can be brought about by the addition of spent mushroom substrate.

Análise fitoquímica e potencial alelopático das cascas de Pouteria ramiflora na germinação de alface

Alelopatia é a capacidade que determinadas plantas têm de interferir no metabolismo de outras, por meio de substâncias liberadas no ambiente, podendo ser uma alternativa de combate às plantas invasoras, dispensando ou reduzindo a utilização dos herbicidas. Levando-se em consideração este fator, o objetivo deste trabalho foi avaliar o potencial alelopático da parte externa e interna da casca de P. ramiflora na germinação e crescimento inicial de plântulas de alface. Os extratos foram obtidos via turbolise, sendo 40 g da planta para 200 mL de água/álcool. Os bioensaios foram diluídos do extrato bruto (20%) em concentrações de 2,5, 5, 10 e 15% e o delineamento estatístico utilizado foi inteiramente casualizado, com médias comparadas pelo teste de Tukey. Não foi observada alteração na germinação nas concentrações dos extratos testados (etanólico e aquoso das partes externa e interna) das cascas de P. ramiflora, além dos extratos também não terem interferido na velocidade de germinação e tempo médio de germinação. Porém, as diferentes concentrações prejudicaram o desenvolvimento da raiz e da parte aérea, principalmente as concentrações de 2,5 e 5,0% do extrato etanólico da parte interna da casca, efeito associado à presença de esteróides e triterpenos, presentes neste extrato. A casca de P. ramiflora, apesar de não afetar negativamente as taxas de germinação, possui a presença de aleloquímicos que interferiram negativamente no crescimento das plântulas de alface, indicando efeito alelopático e potencial de utilização.

Respostas fisiológicas de sementes e plântulas de alface submetidas ao extrato de Philodendron bipinnatifidum

The work was conducted to evaluate the effect of different Philodendron bipinnatifidum Schott. extract concentrations on the physiology and enzymatic metabolism of lettuce seeds and seedlings. The treatments extracts of mature leaves at concentrations of 0, 6, 12, 25 and 50%. Were evaluated the germination, first count germination, speed and germination speed index, length of shoot and primary root, seedling total dry mass, electrical conductivity, chlorophyll content, activity of the enzymes ?-amilase, superoxide dismutase, catalase and ascorbarto peroxidase, lipid peroxidation, hydrogen peroxide content and seedling emergence, length of shoot and total dry mass of emerged seedlings. There was a reduction of germination, germination speed index and total dry mass by increasing the concentration of the extract. While the content of hydrogen peroxide, lipid peroxidation and activity of superoxide dismutase, catalase and peroxidase ascorbarto increased with concentration. The increasing of concentration the leaf extracts of the P. bipinnatifidum negatively affects the activity of the enzyme ?-amylase and causes increase in the activity of antioxidant enzymes, affecting the physiologic performance and growth of lettuce seedlings.

Respostas fisiológicas de sementes e plântulas de alface submetidas ao extrato de Philodendron bipinnatifidum

The work was conducted to evaluate the effect of different Philodendron bipinnatifidum Schott. extract concentrations on the physiology and enzymatic metabolism of lettuce seeds and seedlings. The treatments extracts of mature leaves at concentrations of 0, 6, 12, 25 and 50%. Were evaluated the germination, first count germination, speed and germination speed index, length of shoot and primary root, seedling total dry mass, electrical conductivity, chlorophyll content, activity of the enzymes ?-amilase, superoxide dismutase, catalase and ascorbarto peroxidase, lipid peroxidation, hydrogen peroxide content and seedling emergence, length of shoot and total dry mass of emerged seedlings. There was a reduction of germination, germination speed index and total dry mass by increasing the concentration of the extract. While the content of hydrogen peroxide, lipid peroxidation and activity of superoxide dismutase, catalase and peroxidase ascorbarto increased with concentration. The increasing of concentration the leaf extracts of the P. bipinnatifidum negatively affects the activity of the enzyme ?-amylase and causes increase in the activity of antioxidant enzymes, affecting the physiologic performance and growth of lettuce seedlings.

Switchgrass root exudates have allelopathic potential on lettuce germination and seedling growth

Non-native plant species may inhibit the growth of native vegetation either by competing for resources or by secreting allelochemicals. Switchgrass (Panicum virgatum L.), a perennial grass that is adaptable to a wide range of environments, has recently been introduced to China's Loess Plateau as a forage and as a biofuel source. In this study, we assayed the allelopathic potential of root exudates from 11 switchgrass cultivars (Alamo, Blackwell, Cave-in-Rock, Dakota, Forestberg, Illinois USA, Kanlow, Nebraska 28, Pathfinder, Sunburst, and Unnamed) on lettuce (Lactuca sativa L.) germination and seedling growth. The root exudates were applied to lettuce seeds at three concentrations (1, 10, or 100 mg L−1). Germination percentage (Gp), germination speed (Gs), and allelopathic response index (RI) were calculated to compare the effects of the switchgrass cultivars. The results indicated that lettuce germination and seedling growth generally decreased as the concentration of root exudates increased. Root exudates of Forestberg generally reduced lettuce seedling growth, regardless of the concentration at which the exudates were applied. In contrast, depending on their concentration, root exudates of Nebraska 28 either had no significant effect or increased germination speed and lettuce seedling growth. Cluster analysis showed that Nebraska 28 and Forestberg had the highest allelopathic potential among the switchgrass cultivars. The allelopathic potential of Alamo and Kanlow were similar, suggesting that allelopathic potential is related to ecotype. These results provide important information for additional studies about allelopathic potential of switchgrass and about interactions between switchgrass and neighboring plants.

Phytotoxicity assessment for potential biological control of leafy spurge by soilborne microorganisms

Leafy spurge (Euphorbia esula-virgata), a native of Eurasia, is a serious invasive weed of western grasslands of North America. It is very difficult and cost-prohibitive to control with herbicides; control by insect biological control agents and cultural practices are minimally effective in suppressing vegetative growth and seed production. Current biological control of leafy spurge with pathogens is primarily with mycoherbicides, which require specific environmental conditions and repeated applications to be effective. Alternative biological control approaches using selected microorganisms to attack roots and adventitious shoots may effectively decrease vigor of leafy spurge without environmental manipulations to ensure control efficacy. Our objectives were to survey leafy spurge accessions and their native soils for associated microorganisms, and to assess these microorganisms for potential biological control. A proposed screening protocol, consisting of primary and secondary assays, effectively detected bacteria and fungi with high phytotoxicity toward leafy spurge. Primary lettuce seedling bioassays indicated that 62 % of rhizosphere and 54 % of endorhizal bacteria significantly (P = 0.05) inhibited root growth, causing necrotic lesions. Over 60 % of fungal isolates bioassayed on rice agar significantly inhibited root growth of lettuce seedlings. The most effective microbial isolates, based on primary bioassays, were screened directly on leafy spurge cuttings in secondary assays. Only intact cells of bacteria were detrimental to leafy spurge, indicating that host-bacterial contact was required for pathogenicity. Culture filtrates of 40 % of the test fungi caused complete chlorosis and leaf wilting. The most effective fungi originated from leafy spurge adventitious shoots. Results of the survey suggest that leafy spurge rhizospheres and adventitious shoots are potential sources of biological control microorganisms, which should be considered for inclusion in comprehensive management programs for leafy spurge.

Managing compost stability and amendment to soil to enhance soil heating during soil solarization

Soil solarization is a method of soil heating used to eradicate plant pathogens and weeds that involves passive solar heating of moist soil mulched (covered) with clear plastic tarp. Various types of organic matter may be incorporated into soil prior to solarization to increase biocidal activity of the treatment process. Microbial activity associated with the decomposition of soil organic matter may increase temperatures during solarization, potentially enhancing solarization efficacy. However, the level of organic matter decomposition (stability) necessary for increasing soil temperature is not well characterized, nor is it known if various amendments render the soil phytotoxic to crops following solarization. Laboratory studies and a field trial were performed to determine heat generation in soil amended with compost during solarization. Respiration was measured in amended soil samples prior to and following solarization as a function of soil depth. Additionally, phytotoxicity was estimated through measurement of germination and early growth of lettuce seedlings in greenhouse assays. Amendment of soil with 10%(g/g) compost containing 16.9mg CO2/gdry weight organic carbon resulted in soil temperatures that were 2–4°C higher than soil alone. Approximately 85% of total organic carbon within the amended soil was exhausted during 22days of solarization. There was no significant difference in residual respiration with soil depth down to 17.4cm. Although freshly amended soil proved highly inhibitory to lettuce seed germination and seedling growth, phytotoxicity was not detected in solarized amended soil after 22days of field solarization.

Effect of Aqueous Extract of Biochar on Germination and Seedling Growth of Lettuce (Lactuca sativa L.)

Effect of Aqueous Extract of Biochar on Germination and Seedling Growth of Lettuce (Lactuca sativa L.)

Potencial alelopático de extratos aquosos de aroeira sobre germinação e crescimento de plântulas de alface

The objective of this work was to analyze and to describe the influence of aqueous extracts of S. terebinthifolius Raddi over achenes and the growth of seedlings of lettuce cv. ‘Branca de Boston’. The extract was acquired from plants collected in the campus of UFPel. The essays were accomplished at laboratory, and the concentrations were zero, 50 and 100% of aqueous extracts of leaves (vegetal fresh material, w/v). Achenes of lettuce cv. ‘Branca de Boston’ were put to soak for 60 minutes in different extracts concentrations and than the tests: germination, first counting of germination, germination speed rate, length of the seedlings, fresh and dry mass and electrical conductivity. It could be concluded that the extract exerts negative effect of phytotoxicity over the achenes and over the growth of lettuce seedlings, in both concentrations used, being more expressive according to the increase of the extract concentration.

Contribution of militarine and dactylorhin A to the plant growth‐inhibitory activity of a weed‐suppressing orchid, Bletilla striata

The methanol extract of Bletilla striata, an ornamental orchid in eastern Asia, exhibited plant growth‐inhibitory activity. It was purified by continuous chromatography, based on the inhibitory activity against the growth of lettuce seedlings, resulting in two glycosidic compounds, militarine and dactylorhin A. The EC50 values of militarine and dactylorhin A against the radicle elongation of the lettuce seedlings were 0.28 and 0.88 mmol L−1, respectively. The amount of militarine and dactylorhin A in the methanol extract of the aerial part of B. striata was calculated to be 5.6 and 7.5 mg g−1 fresh weight, respectively. The inhibitory activity of militarine and its content in the methanol extract revealed that the plant growth‐inhibitory activity of the extract of B. striata was mainly related to militarine. The inhibitory activity of militarine against the growth of Italian ryegrass and timothy were of the same level as that of lettuce.